Epidemiology, microbiology, and pathology

Amebiasis results from gastrointestinal infection by the protozoon E. histolytica. Amebic dysentery was described in ancient times by Galen and Hippocrates, and even earlier descriptions of dysentery-like illness were found in Assyrian and Babylonian writings [Cox, 2002]. The role of E. histolytica in causing pathogenic intestinal and hepatic lesions was described definitively by [Kartulis 1886] and [Councilman and Lafleur 1891]. Its distribution is global, although it is more common in regions that have hot, humid climates. Despite its partiality for tropical climates, the organism was first isolated from a stool sample by Lösch in St. Petersburg, Russia, in 1873, and an outbreak of amebiasis occurred at a Chicago hotel at the time of the 1933 World’s Fair, resulting in about 100 deaths.

Gross postmortem examination of the brain reveals abscesses, petechiae, and suppurative meningitis. Necrotic areas are distributed throughout the brain but are concentrated in the basal ganglia and frontal lobes. Cerebral edema and transtentorial herniation are often seen. Microscopic study demonstrates a zone of disruption; necrotic areas are more common than areas of inflammation. The inflammatory response is attended by mononuclear cells [Lombardo et al., 1964].

Clinical characteristics, clinical laboratory tests, and diagnosis

From the intestine, the liver, lungs, and brain are secondarily affected. Cerebral amebiasis is the most unusual condition and principally occurs in patients with hepatic or pulmonary infections. Most patients with cerebral amebiasis have symptoms that accompany the effects of systemic disease, such as fever, weight loss, and anorexia. Cerebral amebiasis is rare, and many of the patients who have this disorder do not manifest neurologic symptoms. In one series, only 5 of 17 patients had neurologic manifestations, consisting of increased intracranial pressure, hemiplegia, meningeal irritation, nuchal rigidity, confusion, and headache [Lombardoet al., 1964]. The presence of a focal CNS lesion in a febrile patient with hepatic or intestinal disease should suggest amebiasis, particularly if there is a history of travel to an endemic area and if more common causes, such as bacterial brain abscesses or tumors, have been ruled out [Durack, 1997].

The diagnosis of cerebral amebiasis can usually be confirmed by serologic evaluation using an indirect hemagglutination assay or indirect immunofluorescent staining. Commercial kits are available for detection of ameba antigen, and the polymerase chain reaction has been used for detecting Entamoeba DNA [Leber and Novak, 1999; Tanyuksel and Petri, 2003]. CSF evaluation is usually not helpful; cultures are usually sterile, and cytology or changes in the protein or glucose concentrations are nonspecific. The polymerase chain reaction applied to fluid drained from a brain abscess in an adult detected E. histolytica DNA, though intact amebas were not seen [Ohnishi et al., 1994]. In a pediatric case, intact amebas were recovered in fluid aspirated from the thorax but were not detected in the child’s stool [Hughes et al., 1975]. Stool cultures are usually negative when nervous system involvement appears. Neuroimaging may reveal abscess formation with perilesional edema [Tikly et al., 1988]. General testing for amebic colitis and liver abscess is reviewed in Tanyuksel and Petri [2003].

Management

Cerebral amebiasis is rarely treated successfully. Metronidazole is currently the preferred drug (15 mg/kg initially followed by 30 mg/kg/day divided into four doses) [Strickland, 1992], although trinidazole may be more effective than metronidazole [Medical Letter, 2004]. Emetine and chloroquine are alternative medications.

A combination of metronidazole and chloroquine was used successfully in treating a pediatric case of cerebral amebiasis with three abscesses [Hughes et al., 1975]. Amebiasis in an adult was treated with metronidazole and dehydroemetine after drainage of a brain abscess [Ohnishi et al., 1994]; the patient recovered, with minor neurologic impairment. An adult male in a stuporous state, with signs of encephalitis and hepatic abscesses, had a low titer for E. histolytica by indirect hemagglutination, but countercurrent immunoelectrophoresis was positive [Schmutzhard et al., 1986]. CT scans of the brain exhibited approximately 40 small ringlike lesions, mostly in the white matter of both hemispheres. Treatment with metronidazole, chloroquine, and tetracycline effected a partial recovery; further regression of the lesions and recovery occurred after a course of dehydroemetine treatment. Paromomycin has been used for asymptomatic cases [Medical Letter, 2004].

Epidemiology, microbiology, and pathology

Primary amebic meningoencephalitis (PAM) is a fulminant disease occurring in children and young adults. The disease was first reported from Australia and was initially attributed to Acanthamoeba [Fowler and Carter, 1965], which previously had been found to cause death of mice inoculated intranasally with amebas [Culbertson et al., 1958]. The disease was soon reported from Florida and was then characterized as PAM [Butt, 1966]. N. fowleri is a free-living, facultative parasite, with a life cycle that includes an ameboid trophic (feeding) stage, a transitory flagellate stage, and a double-walled cyst able to withstand desiccation. The amebas measure about 15–30 μm, and cysts from 7 to 15 μm in diameter. The ameba is found in water, soil, sewage, or other decaying organic material where there is a bacterial food source [Marshall et al., 1997], and grows optimally at elevated temperatures (37–45°C). Of an estimated 200 cases since the first descriptions of PAM, more than 90 percent of the patients have died. The disease has been reported from Australia, Belgium, Czech Republic, Great Britain, Mexico, India, New Zealand, Nigeria, and the United States. Extended descriptions of the organism and the disease can be found in several review articles [Barnett et al., 1996; Duma, 1984; John, 1993].

In the United States, most of the cases have developed in the southern tier of the country, where warm water conditions are more likely to be encountered. In Florida, where a number of cases have been reported after swimming in lakes, the probability of infection was estimated to be 1 case per 2.6 million exposures [Wellings, 1977]. No cases have resulted from drinking water containing amebas.

Typically, infection with N. fowleri occurs while swimming or washing in warm, fresh water containing the amebas, and early manifestations of the disease ensue. Bodies of water associated with amebic infections have included ponds, man-made lakes, hot springs, wading pools, irrigation canals, thermally polluted streams, and inadequately chlorinated swimming pools. Those affected are children or young adults without underlying disease. Infection has been associated with prolonged immersion in water, diving, underwater swimming, or other activities that allow water to enter the nostrils. Well water that was used to bathe a child was believed to be the source of Naegleria in a 6-month-old child who died with PAM [Hebbar et al., Annls of Trop Peds, 2005]. The onset of PAM is usually within 2–3 days after exposure. Amebas enter the nasal passages and gain access to the nervous system by penetrating the olfactory mucosa, entering the submucosal nervous plexus, migrating along the olfactory nerves, and traversing the cribriform plate. Hemorrhagic destruction of gray matter and devastation of the olfactory bulbs follow sanguinopurulent meningitis and pronounced brain edema [Martinez et al., 1973]. Spinal cord involvement is signaled by similar gray-matter disruption. Perivascular infiltrates include leukocytes and amebas (Figure 82-10). Numerous eosinophils may be present. Simultaneous bronchopneumonia and pulmonary edema, myocarditis, and splenitis may occur.

Fig. 82-10 Section through cerebral cortex of an individual with primary amebic meningoencephalitis.

There are large numbers of Naegleria fowleri amebas in the perivascular space. (Hematoxylin-eosin.)

Clinical characteristics, clinical laboratory tests, and diagnosis

Among the most common symptoms of PAM are severe headache, stiff neck, nausea, vomiting, fever (39–40°C), behavioral changes, seizures, diplopia, and coma [Duma, 1984; Martinez, 1985]. One patient complained of a violent headache and foul odors before becoming unconscious [Duma, 1984]. Distortion of taste has also been reported [Martinez, 1993]. CSF is typically cloudy with a slightly decreased glucose concentration, increased protein content (75–970 mg/dL), and innumerable white blood cells (300–24,600/mm³) and erythrocytes [Martinez, 1985]. Polymorphonuclear cells make up 52–99 percent, lymphocytes 1–48 percent, and monocytes 1–2 percent of the white blood cells in the CSF. High opening pressures may be observed.

Differential diagnosis for PAM is bacterial meningitis, but the CSF is sterile in PAM [Martinez, 1993]. A Gram stain of the CSF is not particularly helpful in diagnosis because the amebas may lyse during preparation of the slide. In freshly obtained spinal fluid, motile Naegleria amebas can usually be seen in wet-mount preparations [Lowichik and Ruff, 1995], which are best viewed with a phase-contrast microscope. The CSF should not be refrigerated or frozen before examination. Low-speed centrifugation of the sample may help concentrate the amebas and make them easier to find. In CSF from three PAM patients, amebas numbered from 26 to 118/mm³, as compared with 330 to more than 9000 leukocytes/mm³ [Duma et al., 1971]. The amebas can be recognized by their relatively swift movement with an anterior, eruptive pseudopod (Figure 82-11), contrasting with the sluggish motility of the leukocytes with indistinct pseudopodal activity. As an aid in diagnosis, amebas can be readily cultured on non-nutrient agar plates spread with a suspension of Escherichia coli as a food source [Visvesvara, 1999]. Although not widely available, molecular testing may prove to be a sensitive method for testing even archived samples [Schild et al., 2007]. Immunofluorescent staining for Naegleria antibodies in acute-phase serum is of little diagnostic value because of the fulminant nature of the disease and a delayed humoral response.

Fig. 82-11 Naegleria ameba from culture in wet mount.

An ectoplasmic pseudopod is present at the anterior end of the ameba. When seen in cerebrospinal fluid samples, the clear pseudopod and rapid movement (approximately 1 μm/second) distinguishes Naegleria amebas from sluggishly motile leukocytes that may also be present in the cerebrospinal fluid. The nucleus is indicated by an arrow; some rod-shaped bacteria (Escherichia coli) can also be seen. Bar measures 10 μm. (Interference-contrast.)

Neuroimaging is not particularly helpful in diagnosis, with results being nonspecific. CT and MRI scans of a 9-year-old child hospitalized with what was diagnosed upon postmortem examination as PAM showed no abnormalities at time of admission [Kidney and Kim, 1998]. Three days later, 1 day before the child died, a CT scan indicated developing hydrocephalus and brain edema but no focal lesions.

Management

The high mortality from PAM may be a consequence of delays in diagnosis and initiation of antimicrobial therapy. Early diagnosis and intensive care may improve the small chance of recovery [Seidel, 1985a]. Differences in virulence of PAM ameba isolates, when tested by mouse inoculations, indicate that this may be a factor affecting survival. Naegleria amebas are sensitive to amphotericin B, the drug of choice in treating PAM. In a well-documented PAM case, the patient, a 9-year-old female, had been swimming in a California hot spring before developing symptoms of meningoencephalitis. She was given intravenous and intrathecal amphotericin B and miconazole, oral rifampin, and sulfisoxazole, and recovered with minimal neurologic sequelae [Seidel et al., 1982]. Other successful treatments have been reported [Apley et al., 1970; Brown, 1991; Jain et al., 2002; Wang et al., 1993]. The macrolide azithromycin has demonstrated amebacidal activity in vitro and in the mouse model and may have potential for treating primary amebic meningoencephalitis [Goswick and Brenner, 2003]. Although azithromycin penetrates the brain, its low concentration in CSF may render it less effective in PAM [Jaruratanasirikul et al., 1996]. Despite a small number of successful treatments, most cases are fatal [Seidel, 1985a]. Various combination therapies have been attempted, including amphotericin B/azithromycin and amphotericin/fluconazole/rifampin, and may improve outcomes [Soltow and Brenner, 2007; Vargas-Zepeda et al., 2005].

Epidemiology, microbiology, and pathology

It was largely through the observations of Culbertson that free-living amebas were recognized as potentially pathogenic organisms. He detected acanthamoebas in monkey kidney cell cultures used for growing poliovirus, and demonstrated their pathogenicity in mice [Culbertson et al., 1958].

Two different, although closely related amebas, cause granulomatous encephalitis: Acanthamoeba spp. and Balamuthia mandrillaris. Acanthamoeba granulomatous encephalitis is an opportunistic, chronic disease that may have a prodromal period of weeks to months, with most patients being immunocompromised [Martinez, 1980]. Predisposing factors to acanthamebiasis include steroid treatments, autoimmune conditions, organ transplants, chemotherapy, radiation therapy, alcoholism, and pregnancy [Martinez, 1980; Cha et al., 2006]. A small number of Acanthamoeba granulomatous encephalitis cases have been described in immunocompetent children.

Acanthamoeba is perhaps the most common ameba found in soil, which is often the source of infection. It is remarkably tolerant of a range of environmental conditions and can be isolated from seawater and fresh water, and from Arctic soils and beach sands. Acanthamoeba is also found in the home in aquaria, flowerpot soil, humidifiers, sink taps, and drains. It has been isolated from hot tubs, hydrotherapy baths, dental irrigation equipment, and laboratory eye wash stations. The life cycle consists of alternating ameboid and cyst stages. Cysts are particularly resistant to both physical (heat, desiccation, drying) and chemical (chlorine, antimicrobials) agents, and have remained viable in the laboratory in excess of 20 years. Infection may take place through breaks in the skin that are contaminated with soil, or by inhalation of airborne ameba cysts originating from soil. In surveys of healthy groups of individuals (students, military recruits), Acanthamoeba has been cultured from the nasal passages, indicating exposure and infection but not disease [Badenoch et al., 1988; Cerva et al., 1973].

Clinical characteristics, clinical laboratory tests, and diagnosis

In addition to encephalitis, Acanthamoeba can cause nasopharyngeal, cutaneous, and disseminated infections. Nasopharyngeal and cutaneous infections can be precursors to disseminated amebiasis or encephalitis, as amebas spread from their initial portal of entry. The CNS becomes infected by hematogenous transport of amebas, either from the lungs or from cutaneous lesions. A granulomatous reaction occurs, which can be seen in histopathologic slide preparations, but this reaction may be absent in immunocompromised hosts [Martinez, 1980]. Areas of the brain affected are usually the cerebrum, cerebellum, and brainstem, where the amebas produce hemorrhagic necrotic lesions; large numbers of amebas can be found in the perivascular areas of brain tissue. Cysts of Acanthamoeba may be seen in histopathologic sections; Naegleria amebas do not form cysts in tissue. Reports of detecting amebas in CSF are rare. Because of the absence of clear pathognomonic symptoms, Acanthamoeba granulomatous encephalitis is often unrecognized and diagnoses are often made postmortem.

Because the disease is chronic, an antibody response develops over time and the infection can be diagnosed by indirect immunofluorescence staining of the patient’s serum. Surveys of human populations for Acanthamoeba antibodies have found that many healthy people have elevated antibody titers, probably resulting from exposure to the amebas through contact with soil or water [Cerva, 1989; Cursons et al., 1980].

Clinical features are variable but typically have a subacute to chronic presentation, with fever, headache, seizures, personality change, lethargy, or confusion. Cranial nerve palsies, meningeal signs, or hemiparesis may be seen on physical examination [Cha et al., 2006]. Diagnosis of Acanthamoeba granulomatous encephalitis is difficult and the disease mimics other types of encephalitis. Children infected with Acanthamoeba have exhibited headache, stiff neck, vomiting, abnormal behavior, fever, ataxia, and tonic-clonic seizures [Karande et al., 1991; Sharma et al., 1993; Singhal et al., 2001]. Hydrocephalus may also develop [Karande et al., 1991]. Differential diagnoses include neurotuberculosis and neurocysticercosis. Although the amebas are generally not recovered from CSF, several cases were reported in which the amebas were seen in wet-mount preparations of spinal fluid, and/or were cultured from CSF [Callicot et al., 1968; Karande et al., 1991; Kidney and Kim, 1998; Sharma et al., 1993]. In wet-mount slide preparations, trophic Acanthamoeba have radiating fingerlike pseudopodia over the surface and are relatively slow-moving amebas. More often, amebas are cultured from biopsied brain tissue or skin ulcers on to plates of non-nutrient agar coated with E. coli and incubated at 37°C [Visvesvara, 1999]. Recently developed molecular techniques may also be helpful in making the diagnosis [Yagi et al., 2007; Qvarnstrom et al., 2006; Yagi et al., 2008]. CSF protein is elevated (range 31–500 mg/dL), as is the white blood cell count (14–750 cells/μL) and glucose level (17–240 mg/dL); among the white blood cells are lymphocytes (19–100 percent) and polymorphonuclear leukocytes (2–70 percent) [Martinez, 1980, 1985]. The CSF protein in an 8-year-old female with Acanthamoeba meningitis increased from 200 mg/dL at onset to a high of 500 mg/dL, and then decreased to 41 mg/dL after completion of drug therapy 5 months after the patient was first seen [Singhal et al., 2001]. Neuroimaging by MRI of an adult male diagnosed with acanthamebiasis revealed punctate focal lesions, mainly in the cerebellar hemispheres, and fewer lesions in the cerebral hemispheres and the corpus callosum [Kidney and Kim, 1998]. Sequential MRIs often show a rapidly expanding brain mass [Gene et al., 2007].

Unrelated to its role as etiologic agent of Acanthamoeba granulomatous encephalitis, Acanthamoeba can also cause amebic keratitis as a result of corneal trauma or wearing contact lenses. Ophthalmic solutions prepared from nonsterile tap water, and lens cases that harbor bacterial biofilms can support growth of the amebas. Keratitis has not been reported to develop into encephalitis; however, a child diagnosed with uveitis and pharyngitis caused by Acanthamoeba went on to develop fatal encephalitis [Jones et al., 1975].

Management

There are several reported cases of acanthamebiasis in pediatric HIV/AIDS patients. An 8-year-old patient developed cutaneous and sinus lesions, in which Acanthamoeba cysts and trophozoites were seen, along with a weak granulomatous response [Friedland et al., 1992]. The infection progressed after about 3 months to disseminated disease with CNS involvement (multiple lesions within the right basal ganglia by MRI) and ultimately proved fatal, despite treatment with ketoconazole, fluconazole, sulfadiazine, and trimethoprim-sulfamethoxazole. Acanthamebiasis in another pediatric case with congenital HIV/AIDS developed as osteomyelitis and subcutaneous abscesses without neural involvement [Selby et al., 1998]. Initial treatment was with oral fluconazole but was subsequently changed to intravenous pentamidine, oral flucytosine (5-fluorocytosine), and oral itraconazole, and disease progression was halted. In both adult and pediatric acanthamebiasis, death is usually a consequence of multiple AIDS-related infections rather than from the amebic infection per se.

Acanthamoeba infections of the CNS are usually fatal, although some reports of successful antimicrobial treatment are described. Often, however, the same antimicrobial agents used successfully in one case are unsuccessful in other acanthamebiasis cases. Response to therapy depends, to a large extent, on infective dose of amebas, virulence of the infecting strain, the time at which diagnosis is made, the extent of dissemination of the infection, and the immune status of the patient. As yet, the optimal antimicrobial therapy for treatment of Acanthamoeba encephalitis is unclear. Most recoveries have been treated successfully with combinations of antimicrobials: sulfadiazine, pyrimethamine, and fluconazole in an adult HIV/AIDS patient [Martinez et al., 2000], and ketoconazole, rifampin, and trimethoprim-sulfamethoxazole in two pediatric patients [Singhal et al., 2001]. Surgical excision may be warranted in some, if not all, cases [Fung et al., 2008]. In vitro studies suggest that miltefosine and voriconazole have activity against Acanthamoeba [Schuster et al., 2006].

Epidemiology, microbiology, and pathology

Balamuthia granulomatous encephalitis was initially described in immunocompromised humans [Anzil et al., 1991; Visvesvara et al., 1990], but more recent cases have occurred in immunocompetent children [Bakardjiev et al., 2003; Duke et al., 1997; Reed et al., 1997; Rowen et al., 1995]. The importance of Balamuthia as a CNS pathogen is increasingly recognized [Matin et al., 2008]. The life cycle comprises trophic and cystic stages; the cyst is a triple-layered structure without pores. Little is known about the ecology of the ameba, other than that it is found in soil. Like Acanthamoeba, it is likely to enter the body by inhalation of cysts in windblown soil, or through breaks in the skin contaminated by soil, followed by hematogenous spread. Balamuthiasis can develop as cutaneous, nasopharyngeal, or CNS lesions. In a review of 30 cases reported from Peru, all developed initially as cutaneous lesions, mostly on the nose or the central region of the face, and progressed to infections of the CNS [Bravo and Sanchez, 2003]. The disease may be chronic, with a prodrome that can extend as long as 2 years, but it often presents in an acute form [Bakardjiev et al., 2003]. The long incubation period makes it difficult to pinpoint the source and time of infection. A 3-year-old female may have become infected through playing with soil in a flowerpot, from which Balamuthia was subsequently isolated (Figure 82-12) [Schuster et al., 2003]. Evidence of exposure to Balamuthia among healthy individuals is seen in elevated serum antibody titers in studies performed in Australia and the United States [Huang et al., 1999; Schuster et al., 2001]. The relative prevalence of Balamuthia granulomatous encephalitis in Hispanics is high [Schuster et al., 2004]; in the United States, about 50 percent of cases occurred in Hispanic Americans (who comprise approximately 12 percent of the U.S. population), and almost half of the number of cases worldwide have been described from Latin America and Mexico [Bravo and Sanchez, 2003; Galarza et al., 2002; Martinez et al., 1994; Recavarren-Arce et al., 1999; Taratuto et al., 1991; Uribe-Uribe et al., 2001]. The reasons for the high proportion of Hispanics with balamuthiasis could be because of genetic susceptibility, or environmental or sociologic factors, or a combination of these factors.

Fig. 82-12 Indirect immunofluorescent antibody-stained section of the brain of a 3-year-old child with Balamuthia granulomatous encephalitis.

The amebas are clustered in a pavement-like arrangement around a blood vessel. Other amebas have moved away from the perivascular region into the brain tissue. (Fluorescence microscope.)

(Courtesy of Dr. GS Visvesvara.)

Clinical characteristics, clinical laboratory tests, and diagnosis

Symptoms of Balamuthia granulomatous encephalitis include fever, headache, vomiting, ataxia, hemiparesis, tonic-clonic seizures, cranial nerve palsies (particularly third and sixth cranial nerves), and diplopia [Bakardjiev et al., 2003; Martinez and Visvesvara, 2001; Schuster et al., 2009]. Areas of the brain that are typically infected are the basal ganglia, midbrain, brainstem, and cerebral hemispheres [Martinez and Visvesvara, 1997]. Otitis media has preceded the onset of Balamuthia granulomatous encephalitis in several pediatric cases [Bakardjiev et al., 2003; Kodet et al., 1998; Rowen et al., 1995]. CSF may have mild to markedly elevated protein and leukocyte levels, but normal or slightly decreased glucose. Hydrocephalus develops in many cases [Duke et al., 1997; Kodet et al., 1998; Schuster et al., 2009]. Because of its vague symptomatology, diagnosis of balamuthiasis requires a high index of suspicion on the part of the physician, and differential diagnoses include bacterial or viral encephalitis, neurotuberculosis, and neurocysticercosis [Bakardjiev et al., 2003]. What was initially identified as brainstem glioma in an infant was, at postmortem examination, recognized as a Balamuthia infection [Lowichik et al., 1995]. Balamuthia granulomatous encephalitis should also be considered in patients with suspected herpes simplex virus encephalitis when testing for the virus yields negative results [Deetz et al., 2003; Reed et al., 1997].

Most diagnoses of the disease are made at postmortem examination. In histopathologic sections of brain tissue, the amebas are found in large numbers within perivascular areas. Because of the chronic nature of the disease, an antibody response to Balamuthia develops over the course of the infection and is the basis for indirect immunofluorescent staining as a diagnostic aid. Likewise, immunohistopathology is useful for visualizing amebas in brain and other tissues. Neuroimaging is helpful in making a diagnosis [Deetz et al., 2003; Healy, 2002]; the presence of single or multiple space-occupying or ring-enhancing lesions may be indicative of balamuthiasis (Figure 82-13). Neuroimaging may also show evidence of enlarged ventricles and atypical demyelinating lesions [Schuster et al., 2009]. In brain and other tissue sections, the ameba is difficult to distinguish from Acanthamoeba because the organisms have similar morphologies. Trophic Acanthamoeba are somewhat smaller (approximately 20 μm) than Balamuthia (approximately 5 μm), though multiple nucleoli are sometimes seen in Balamuthia nuclei. Both amebas form cysts in tissue, but Balamuthia cysts are larger (up to 30 μm) and have a wrinkled wall without pores. Immunofluorescent staining, however, can distinguish between the two amebas. Affected brain tissue often shows areas of necrosis with surrounding areas of ayptical reactive astrocytes and inflammatory cells [Perez and Bush, 2007]. Balamuthia cannot be readily cultured from biopsied tissues because the organism grows slowly and requires tissue culture cells as a feeder layer. Attempts to culture Balamuthia from macerated brain tissue have taken from 10 to about 30 days at 37°C. Polymerase chain reaction technology is available for identification of Balamuthia DNA in tissues and in CSF but is largely limited to research laboratories (e.g., California Department of Health Services, Viral and Rickettsial Disease Laboratory, Richmond; Ohio State University, Department of Molecular Genetics, Columbus) [Schuster et al., 2009; Yagi et al., 2008]. A multiplex, real-time polymerase chain reaction has recently been developed with the ability to detect Balamuthia, Acanthamoeba, and Naegleria simultaneously [Qvarnstrom et al., 2006].

Fig. 82-13 Magnetic resonance image of the brain of a 2-year-old with Balamuthia amebic encephalitis.

The arrow points to a space-occupying lesion in the right occipitoparietal region of the brain.

Management

Of the approximately 150 recognized Balamuthia cases, successful outcomes have been reported in three individuals [Deetz et al., 2003; Jung et al., 2004], one of them a 5-year-old female. Therapy included flucytosine, pentamidine isethionate, fluconazole, sulfadiazine, and a macrolide antibiotic (azithromycin or clarithromycin). In vitro testing of antimicrobials on clinical isolates indicates varied sensitivity to some of the drugs. Pentamidine, however, is particularly effective against all isolates in vitro [Schuster and Visvesvara, 2004], but the drug is slow to cross the blood–brain barrier and has marked toxicity [Donnelly et al., 1988].

Epidemiology, microbiology, and pathology

The microsporidia are opportunistic pathogens, and the majority of these infections have been reported from highly immunosuppresssed cases, including individuals with HIV/AIDS and occasionally solid organ transplant patients [Mohindra et al., 2002]. Cases in immunocompetent individuals are rare. Most infections in humans have been attributed to Enterocytozoon bieneusi, which can cause cachexia, chronic diarrhea, and cholangitis. Encephalitozoon spp. infections are less frequently identified. In recent years, three species (Encephalitozoon hellem, Encephalitozoon intestinalis, and Encephalitozoon cuniculi) have been detected, with a range of presentations including hepatitis, peritonitis, keratoconjunctivitis, nephritis, cystitis, bronchiolitis, sinusitis, diarrhea, and disseminated infection. Different species appear to be associated with different clinical syndromes: E. intestinalis can present with chronic diarrhea and cholangitis, E. hellem can often cause conjunctivitis, and E. cuniculi is associated with disseminated infections, neurologic symptoms, or renal failure [Fournier et al., 2000].

The life cycle consists of an infective spore stage, in which the spore may be as small as a bacterium (typically 1–2 μm by 2–5 μm), and an intracellular proliferative stage that ultimately develops into spores. On release from infected cells, spores may be found in urine, sputum, conjunctival fluid, feces, and CSF, depending on the site of infection. Spores discharged in urine can contaminate ground water, which is a possible source of infection. Ingestion of spores is the most common route of infection for all species, although transplacental infection is known for nonhuman mammals, particularly carnivores [Didier and Bessinger, 1999; Weber et al., 1994]. Other routes of infection include zoonotic transmission and aerosol dispersal. Depending on species, spore germination and discharge occur in the presence of enterocytes, respiratory and nasal epithelial cells, corneal epithelial cells or stroma, and macrophages as primary sites of infection. Infection may be secondarily spread to the kidneys and the CNS by macrophages.

Clinical characteristics, clinical laboratory tests, and diagnosis

Human microsporidial infections of the nervous system occur principally in HIV/AIDS adults. Disseminated infection with renal failure in the setting of underlying severe immunosuppression is frequently described. Patients with CNS involvement can present with cognitive dysfunction, visual impairment, and seizures [Fournier et al., 2000; Leder et al., 1998]. Pediatric cases of microsporidiosis in the CNS have been rarely reported . The first recognized case of human microsporidiosis due to E. cuniculi was in a 9-year-old Japanese male with severe headache, vomiting, and convulsions. The child lived on a farm and had contact with a variety of farm animals, and an animal reservoir is likely to have been the source of the infection [Matsubayashi et al., 1959]. In 1984, a second reported pediatric case occurred in a child from Colombia, who was adopted by a Swedish family and developed convulsions [Bergquist et al., 1984]. The child was successfully treated with carbamazepine and an anticonvulsive drug, and, aside from later minor arthritic symptoms that may have been sequelae of the microsporidial infection, remained in good health. The tentative diagnosis in both cases was based on light microscopy detection of Toxoplasma-like bodies, which were actually microsporidial spores, seen in CSF and urine. The infection was transferable to mice by intraperitoneal injection of the patient’s CSF, urine, or blood. Identification of the species at the time remained inconclusive because diagnostic techniques to distinguish among Encephalitozoon-like microsporidia were not yet available. Based on morphologic distinctions from Toxoplasma, the infective agent was tentatively identified as Encephalitozoon spp. [Weber et al., 1997]. In the second case, serologic studies also detected the presence of immunoglobulin G and immunoglobulin M antibodies against E. cuniculi.

A third reported case was in a 9-year-old black female with congenital HIV/AIDS and a CNS tumor, who developed tonic clonic seizures and died after 8 days in the hospital [Yachnis et al., 1996]. Her symptoms before hospitalization included aphasia, hallucinations, inability to walk, and reduced consciousness. A CT scan exhibited multiple lesions in the cortical gray matter and at the gray–white junction. At postmortem examination, necrotic lesions were found in the cerebral cortex, cerebellum, pons, and medulla. Macrophages and astrocytes in histopathologic sections were filled with spores located in vesicles. Free spores released from destroyed cells were seen in the perivascular spaces. Spores were recognized in hematoxylin-eosin sections, in Gram- and Giemsa-stained preparations, and by polarization microscopy, and were later identified as Trachipleistophora anthropophthera.

Clinical suspicion, in most cases, is triggered by exclusion of other more common diagnoses and persistent symptoms suggestive of multi-organ involvement and fever. CT or MRI can reveal multiple ring-enhancing lesions in the brain suggestive of toxoplasmosis, with failure of anti-Toxoplasma therapy to improve these lesions leading to suspicion of microsporidial infection. Detection of the parasite in CSF may be difficult, as the number of spores may be low [Weber et al., 1997].

Diagnosis of infections, in most cases, is by microscopic examination of tissues or body fluids but primarily of urinary sediment, which seems to be almost always positive [Fournier et al., 2000; Weber et al., 1999]. The Gram and Giemsa stains are good for detection of spores, as is hematoxylin-eosin staining. Spores are Gram-positive (purple) or stain blue with Giemsa. The polarization microscope is helpful in visualizing spores because of their birefringence due to the presence of chitin in the spore wall. Body fluids (urine, CSF) containing spores can be inoculated into tissue culture monolayers for cultivation of the parasite [Visvesvara et al., 1999; Weber and Canning, 1999]. Definitive identification of microsporidial species is done by electron microscopy or polymerase chain reaction, or both. MRI reveals multiple ring-enhancing lesions in the brain. A comprehensive review of techniques for identification of microsporidia in clinical specimens is available [Garcia, 2002].

Management

Albendazole and other benzamidazoles, such as thiabendazole, are currently the recommended antimicrobials for treatment of microsporidiosis, although they may not be effective against mature spores [Weber et al., 2000]. The drugs act by binding to tubulin and inhibiting microsporidial divisions. Disseminated infections caused by E. cuniculi are treated in adults with a dose of 400 mg twice a day [Medical Letter, 2004]. While there are no data on drug levels in CSF, the successful use of albendazole in treatment of cerebral cystercercosis suggests diffusion across the blood–brain barrier. In the few patients described, a decrease in the number and size of brain lesions following treatment has been observed, although urinary excretion of spores persisted [Weber et al., 2000].

Epidemiology, microbiology, and pathology

The causal agent of toxoplasmosis was described from a desert rodent, the gondi, in 1908, but it was 1923 before the association with human disease was reported, and 1937 when its role in congenital infections was recognized [Cox, 2002; Remington et al., 2001]. The organism is found worldwide in a variety of mammals and birds. Toxoplasmosis is a major public health problem in both developed and developing countries. Approximately 20–40 percent of the adult population in the United States is seropositive. The cat is the definitive host of the parasite and excretes oocysts in the feces. Ingestion of the oocyst by animals and humans continues the cycle [Frenkel, 1985]. After being ingested by the host, the oocyst releases sporozoites that invade cells, either by active penetration or by phagocytosis, giving rise to rapidly reproducing trophozoites, or tachyzoites. Tachyzoites eventually transform into slower-growing bradyzoites that form intracellular tissue cysts and may remain quiescent for years in the host, particularly in muscle and brain tissues. Cyst formation is triggered by the host’s developing immune response, and the continued release of bradyzoites from tissue cysts stimulates the immune system, resulting in lasting immune protection.

Humans are infected by ingestion of raw or inadequately cooked meat containing tissue or by ingestion of oocysts shed in cat feces. Of the two possible sources of infection, undercooked meat is the more likely vehicle of transmission. Through dissemination of the parasite by tissue cysts in undercooked meats, Toxoplasma has effectively bypassed the need for the cat as an intermediate host, relying entirely upon food as a vehicle for direct transmission; ingestion of undercooked ground beef, rare lamb, and unpasteurized goats’ milk was identified as a risk factor for infection a recent study in the United States [Jones et al., 2009]; [Su et al., 2003]. Risk factors also included the ownership of three or more kittens or having an occupation handling meat products [Jones et al., 2009]. Transfusion of whole blood from asymptomatic carriers can also serve as a mode of transmission. Reactivation of a latent infection can be triggered by the host becoming immunodeficient or immunocompromised.

Intrauterine or congenital toxoplasmosis may develop in the fetus if the mother is infected during pregnancy. The placenta is invaded by parasites from the maternal circulatory system that eventually pass into fetal circulation. Infection may be asymptomatic in the mother; however, the fetus develops a generalized infection involving spleen, liver, eyes, and CNS [Desmonts and Couvreur, 1974; Lowichik and Siegel, 1995]. The incidences of maternal and fetal infection in the United States are 6 and 2 per 1000, respectively [Wilson and Remington, 1992]. The risk of fetal infection increases as the pregnancy progresses: 25 percent in the first trimester, 54 percent in the second trimester, and 65 percent in the third trimester. However, severity of infection is inversely related to when infection occurs during pregnancy. When disseminated, acquired toxoplasmosis produces systemic manifestations consisting of multiple organ infection, including the brain. Calcium is deposited in necrotic cerebral lesions; cerebral calcification is often seen on CT or MRI scans and plain radiographs of neonates (Figure 82-14).

Fig. 82-14 Toxoplasmosis.

A radiograph of the infant skull demonstrates fine intracranial calcifications.

Postmortem examination of brain tissue in the congenital form of the disease reveals pseudocysts or the organism itself. Severe fibrosis of the meninges develops, with resultant thickening. The cortex contains many regions of encephalomalacia. Hydrocephalus is often present. Microscopic study demonstrates large or small granulomas accompanied by glial proliferation and inflammatory infiltrate; areas of nonspecific necrosis are usually present. Giemsa staining delineates the parasite.

Clinical characteristics, clinical laboratory tests, and diagnosis

Clinical manifestations of congenital infection are extremely variable. The well-known clinical constellation of hydrocephalus, cerebral calfications, and chorioretinitis is often not present in affected infants [Petersen, 2007]. The approximate incidence of abnormalities in 180 cases of intrauterine toxoplasmosis included microcephaly (20 percent), hydrocephalus (25 percent), microphthalmia (35 percent), seizures (40 percent), psychomotor retardation (45 percent), cerebral calcification (60 percent), and chorioretinitis (95 percent) [Feldman, 1969]. Other studies have reported similar percentages [Lowichik and Siegel, 1995; Wilson and Remington, 1992]. Approximately 80–90 percent of survivors of overt congenital toxoplasmosis have mental retardation, cerebral palsy, epilepsy, or visual impairment [Stern et al., 1969]. Although the manifestations of some cases have been similar to those of congenital cytomegalic inclusion disease, CNS involvement is usually more common and extensive in toxoplasmosis. Hydrocephalus with a tense or bulging fontanel, vomiting, a high-pitched cry, and opisthotonic posturing may dominate the neonatal period (Figure 82-15). Skull radiographs and ultrasound demonstrate punctate, scattered calcifications and separated cranial sutures. Hydranencephaly also has been reported [Altshuler, 1973], as has infantile diabetes insipidus [Silver and Dixon, 1954] and growth hormone deficiency [Massa et al., 1989]. Delayed onset of seizures, chorioretinitis, and mental retardation can also occur [Miller et al., 1971]. Up to 85 percent of children with congenital toxoplasmosis will develop retinal and choroidal involvement; lesions initially are edematous with hemorrhage, and a yellowish exudate gives rise to areas of peripheral irregular hyperpigmentation with a pale atrophic center [Wilson et al., 1980]. Even in those infants with toxoplasmosis who are asymptomatic at birth, up to 85 percent may develop chorioretinitis or serious neurologic disability by 8.3 years [Wilson et al., 1980]. Toxoplasmosis in the fetus and newborn is reviewed by Remington and colleagues [2001], and methods for diagnosis of the disease are discussed by Wilson and McAuley [1999] and by Wilson and associates [2002].

Fig. 82-15 Hydrocephalus in congenital toxoplasmosis.

Outside the newborn period, the infection is often asymptomatic in the immunocompetent host. Approximately 10 percent of individuals with acute toxoplasmosis will experience a self-limited flulike illness [Montoya and Liesenfeld, 2004]. In contrast, immunosuppressed individuals can develop a life-threatening illness with either acute infection or reactivation. The acquired form of toxoplasmosis causes meningoencephalitis, and long-term sequelae are common [Townsend et al., 1975]. There have been reports of disseminated generalized toxoplasmosis after immunosuppressive therapy in patients receiving transplantation [Ghatak et al., 1970; Khan and Correa, 1997; Seong et al., 1993] and, to a lesser extent, in those with malignancy [Israelski and Remington, 1993]. Immunodeficiency can lead to reactivation of dormant tissue cysts and the release of bradyzoites. Meningoencephalitis, often fatal, is a major complication. Optic neuritis has also been reported in children [Roach et al., 1985]. Although cerebral toxoplasmosis is an important complication of AIDS in adults [Bertoli et al., 1995], it is not common in neonates or older children [Lowichik and Ruff, 1995; Miller and Remington, 1990]. When it is present, children appear to have similar clinical and neuroimaging findings (although less severe) than adults. Maternal HIV infection appears to reactivate a latent toxoplasmosis, which can be transmitted to the fetus. These infants with both HIV and toxoplasmosis usually present at 3–4 months of age with similar symptoms to those seen in infants with severe intrauterine toxoplasmosis infection [Lowichik and Ruff, 1995]. Neuroimaging studies in infants with both infections are similar to those in infants with just toxoplasmosis. However, in older patients, it is frequently difficult to correlate neuroimaging abnormalities in gray–white matter regions or basal ganglia with either infection or the presence of lymphoma [Ciricillo and Rosenblum, 1990]. This subject has recently been reviewed, and there are recommended treatment protocols for children infected with HIV and CNS toxoplasmosis [Khan and Correa, 1997].

Immunologic diagnosis of toxoplasmosis relies on the Sabin–Feldman dye test (which detects live parasites), the direct hemagglutination test, the double-sandwich enzyme-linked immunosorbent assay, the immunosorbent agglutination assay, the complement fixation test, the evaluation of immunoglobulin M levels, and the indirect fluorescent antibody test. Comparative information on commercially available kits for detecting immunoglobulin M in serum samples is available [Wilson et al., 1997]. The antibody test may be the most dependable, but the hemagglutination test is used most often (see Table 82-2). Diagnosis of congenital toxoplasmosis can be especially challenging, and consultation and testing with a laboratory experienced with toxoplasmosis diagnostics is warranted when toxoplasmosis is suspected [Montoya and Rosso, 2005]. Prenatal diagnosis of congenital toxoplasmosis with a polymerase chain reaction test on amniotic fluid is possible and cost-effective [Hohlfeld et al., 1994; Sahai and Onyett, 1996]. Testing of placental testing has a sensitivity of only 25 percent [Filisetti et al., 2010].

Management

The value of therapy for congenital toxoplasmosis has been demonstrated [McAuley et al., 1994]. Early treatment with spiramycin for the mother and sulfadiazine, pyrimethamine, and folinic acid for the infant is beneficial and 70 percent effective [Lowichik and Siegel, 1995; Roizen et al., 1995; Wilson and Remington, 1992; Montoya and Remington, 2008]. Outside the newborn period, treatment is usually not required, except in immunocompromised hosts.

Epidemiology, microbiology, and pathology

Malaria is caused by protozoal parasites of the genus Plasmodium, with life cycle stages alternating between the mosquito and a variety of mammals and birds. Several species of Plasmodium cause malaria in humans – Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, and the recently discovered Plasmodium knowlesi – but P. falciparum is the only member of the genus that has been well documented as affecting the host’s nervous system. Awareness of the disease dates back some 5000 years, with the description of malaria-like symptoms in writings from China, and later in texts from India, Sumer, Egypt, and Ancient Greece [Carter and Mendis, 2002]. Hippocrates (ca. 400 bc) recognized the regular occurrence of febrile episodes of the disease, and used the terms “quotidian” (daily), “tertian” (every 3 days), and “quartan” (every 4 days) to characterize them. The disease derives its name from the misplaced belief that it was caused by miasmas, or “bad air.” The recent sequencing of the P. falciparum genome presents opportunities for development of drugs and vaccines targeted to specific gene products of the parasite [Gardner et al., 2002]. Malaria persists as a major public health problem throughout the world, primarily in developing tropical and subtropical regions. Poverty, poor medical and public health infrastructure, emerging resistance to antimalarial drugs, insecticide-resistant species of mosquitoes, ecologic and practical constraints on drainage of swamps, and limits on widespread use of insecticides make it likely that malaria will persist as an important public health problem for many years to come.

From 200 to 500 million people are affected annually. Malaria’s biggest impact is in sub-Saharan Africa, where it is responsible for at least 20 percent of mortality in young children, or approximately 3000 deaths per day; children younger than 5 years of age account for about 90 percent of the more than 2 million deaths that occur each year. Severe malaria in Africa in children has also been associated with HIV/AIDS, with some studies showing increased incidence, parasite density, and severe clinical illness [Summer et al., 2005].

In endemic areas, such as sub-Saharan Africa, neonates are protected from infection by maternal (transplacental) immunoglobulin G and, in part, from the vestigial presence of fetal hemoglobin. Studies using transgenic mice indicate that the parasite cannot readily break down fetal hemoglobin, thus impairing intraerythrocytic development and replication [Shear et al., 1998]. This protection lasts for about 1 year, after which the infant becomes susceptible to disease. The child of 1–4 years of age is the most vulnerable to infection and the development of severe malaria, with a mortality of about 5 percent. Once this period has passed, the host and parasite exist in a state of détente, with the host exhibiting chronic asymptomatic parasitemia [Kyes et al., 2001]. Additional infections due to continued exposure to parasites from mosquito bites result either in death or in the development of clinical immunity. In endemic areas, a large percentage of adults and children will be infected, but only a small number of these will go on to develop clinical disease [Kyes et al., 2001].

Malaria acquired by recipients of blood transfusions from infected but asymptomatic carriers is also a major problem in endemic regions of the world. Because of more frequent international travel, increasing numbers of cases in adults and children are being recognized in the United States [Emanuel et al., 1993]. A recent report of 30 GeoSentinel sites involving 17,553 travelers observed that malaria was one of the three most frequent causes of systemic febrile illness [Freedman et al., 2006]. Close to 100 cases have appeared in individuals living in the vicinity of or working at airports, probably as the result of inadvertent import of mosquitoes from malarial areas of the world in airplane cabins or luggage [Lusina et al., 2000; Thang et al., 2002]. Of note, the major determinant of outcome in resource-rich areas where malaria is seen infrequently is misdiagnosis, which can occur in 40–50 percent of cases [Summer et al., 2005]. Further, the CDC has estimated that over 80 percent of deaths from malaria in the United States in the last several decades were preventable and were caused by lack of or improper malaria chemoprophylaxis in travelers, delay in establishing diagnosis or misdiagnosis, and/or inappropriate therapy [Summer et al., 2005]. The malaria literature is voluminous and is frequently reviewed, reflecting the importance of the disease [Birbeck, 2004; Maitland and Marsh, 2004; Newton and Krishna, 1998; Newton et al., 2000; Satpathy et al., 2004].

The definitive host and vector, the female Anopheles mosquito, is the site of sexual reproduction of plasmodia. The mosquito injects the organism as sporozoites when it bites humans, who are the intermediate hosts; in humans, the organism undergoes asexual reproduction. The hepatic cells are the first location of asexual reproduction during the pre-erythrocytic phase. Reproduction in hepatic cells is followed by release of parasites that invade erythrocytes during the prepatent period, which lasts 5 or 6 days. The erythrocytic phase, which produces merozoites by schizogony, commences subsequent to the entry of the parasite into the erythrocyte and continues synchronously for 1–3 weeks, which is the incubation period. In its early stages of schizogony, the parasite appears as a ringlike structure within the parasitized erythrocyte. Hemozoin, the product of hemoglobin degradation by the parasite, accumulates in the erythrocyte. Hemolysis of the parasitized blood cells is signaled by chills and fever, with synchrony and periodicity typical for the different Plasmodium spp. For falciparum (subtertian) malaria, the period is about 48 hours. In the bloodstream of the host, some merozoites differentiate into gamete precursors. When the human host is bitten, infected erythrocytes enter the mosquito, carrying micro- and macrogametocytes (male and female gamete precursors), and the cycle begins anew.

The most serious consequence of falciparum malaria for the CNS develops when the parasitized erythrocytes lodge in the brain vasculature. Cerebral involvement follows binding of infected red blood cells to the microvascular endothelium. Sequestration and hemolysis follow and cause obstruction of blood vessels [Sein et al., 1993]. Parasite-induced knobby projections on the surface of infected erythrocytes bind to the endothelial cells in brain, heart, liver, and lungs, causing capillary congestion. By attaching to the endothelial lining of blood vessels, the parasitized erythrocytes effectively avoid destruction that might otherwise occur upon passage through the spleen. This is accompanied by a change in the erythrocyte from a readily pliant state to one of rigidity, which further contributes to blood vessel occlusion. Additionally, rosette formation, resulting from clustering of parasitized and nonparasitized blood cells, may facilitate transfer of parasites from hemolyzed cells to uninfected red blood cells. Local hypoxia, microinfarction, necrosis, hemorrhage, and inflammation subsequently occur. The sequestration and resulting occlusion may deplete the oxygen level in cerebral vasculature, providing a more optimal environment for metabolism and replication of the parasites [Chen et al., 2000]. Thrombi may form and be associated with clotting aberrations, including disseminated intravascular coagulation [Butler et al., 1973]. The blood–brain barrier is disrupted by changes in endothelial cell junctional permeability leading to cerebral edema, more commonly encountered in children than adults [Adams et al., 2002].

A number of theories have been proposed to explain the pathology of cerebral malaria. Hypoxia is one such theory, based on the impedance of blood flow to the brain and the consequent oxygen deficiency. On recovery, however, there is no evidence of the neuronal damage that might be expected to occur as a result of oxygen deprivation. Another explanation is that the surge of mediators that occurs in the CNS may be responsible for the pathology of cerebral malaria [Medana et al., 2001]. Release of proinflammatory cytokines and interleukins (tumor necrosis factor-α, interleukin-1, interleukin-6, nitric oxide lymphotoxin) results in endothelial damage and mimics the clinical condition of sepsis [Clark et al., 2004; Maitland and Marsh, 2004]. Presence of malarial antigens stimulates release of tumor necrosis factor-α, which, in turn, upregulates endothelial adhesion molecules and promotes attachment of parasitized erythrocytes to the vascular lining [Gimenez et al., 2003]. Once parasites are cleared from the blood, the effects of cerebral malaria are reversible and long-term sequelae generally do not develop [Adams et al., 2002]. The role of proinflammatory cytokines in malarial pathology has been reviewed by Clark and associates [2004] in the context of other infectious diseases and noninfectious conditions, and the molecular aspects of cerebral malaria have been reviewed by [Chen et al., 2000].

Postmortem studies of gross specimens demonstrate fulminating cerebral edema and accompanying transtentorial herniation (Figure 82-16). Congestion of arachnoid vessels causes the brain to appear pink or bright cherry-red. Petechiae are evident on the cut surface. Microscopic examination reveals that small arterioles and capillaries are obstructed with parasitized erythrocytes. Mononuclear cells are readily discernible in meningeal and perivascular infiltrates. Microinfarction and ensuing multifocal necrosis and demyelination are widespread.

Fig. 82-16 Cerebral malaria.

Petechial hemorrhages are scattered throughout the brain.

Clinical characteristics, clinical laboratory tests, and diagnosis

The clinical features of malaria are notoriously nonspecific, especially in children. Initial symptoms can include influenza-like illness with fever, chills, rigors, headache, and myalgias. These vague prodromal symptoms precede the development of acute paroxysms of high fever and chills, with the classically described periodic fever patterns observed after several days of untreated illness. Gastrointestinal and repiratory symptoms are also common; a study in Nigeria found that vomiting and abdominal pain were the most common gastrointestinal complaints in children infected with P. falciparum, followed by decreased appetite and diarrhea [Summer et al., 2005]. Lactic acidosis due to metabolic impairment is responsible for respiratory distress [Birbeck, 2004]. Severe hypoglycemia is also common, and is postulated to be due to increased metabolic rate and direct inhibition of gluconeogenesis by the parasite [Summer et al., 2005]; it may be exacerbated further by the hyperinsulinemic effect of the antimalarial treatments, quinidine and quinine.

Cerebral malaria is defined as coma without apparent etiology, inability to localize painful stimuli, and falciparum parasitemia, as demonstrated by blood smears [Birbeck, 2004; Newton and Krishna, 1998; Warrell et al., 1982]. Coma is assessed on the basis of the Blantyre or Glasgow coma scales, taking into account eye movements and motor and verbal abilities. The scales may be of greater value in predicting mortality rather than as a diagnostic tool [Newton and Krishna, 1998].

Cerebral malaria is most often heralded by mental deterioration, particularly confusion or delirium, followed by progression to stupor and coma that transpires during the next 1–3 days. In children, cerebral involvement can be more fulminant, with most patients becoming comatose within 2 days [Molyneux et al., 1989]. New-onset seizures may be confused with febrile seizures in young children [Osuntokun, 1977]. Extensor plantar responses, cerebellar impairment, abnormal movements, and psychosis may also occur [Daroff et al., 1967]. Children are more likely to have decreased tone compared with adults, and impaired brainstem cranial nerve responses and abnormal respiratory function [Molyneux et al., 1989; Newton et al., 1991]. Children with severe illness exhibit evidence of transtentorial herniation [Newton et al., 1991]. Papilledema and extramacular retinal edema are markers of a poor prognosis [Lewallen et al., 1993]. The presence of impaired consciousness, prolonged seizure activity, hypoglycemia, or respiratory distress identifies those at high risk for death or long-term sequelae [Marsh et al., 1995; Steele and Baffoe-Bonnie, 1995]. In one study of 308 children with cerebral malaria, the mortality rate was 14 percent [Bruster et al., 1990].

Severe cerebral malaria can be indistinguishable from other common illnesses, including pneumonia, meningitis, and sepsis, with several case series documenting concurrent bacteremia or meningitis in children. While some studies have not found an association between presumptive antibiotic treatment and improved survival, others have observed that bacteremia is significantly associated with an increased risk of death despite routine use of antibiotics [Gwer et al., 2007].

Neurologic sequelae are not uncommon in children recovering from cerebral malaria. In studies combining data on African children, sequelae develop in about 10–30 percent of patients [Birbeck, 2004; Newton and Krishna, 1998; Bruster et al., 1990]. The depth and duration of coma and multiple convulsions were found to be three independent risk factors for neurologic sequelae in one large prospective study in Gambia, West Africa; the most common neurologic abnormalities were ataxia and paresis, which had resolved in the majority of patients (>95 percent) by 6 months post infection. Other sequelae observed include epilepsy, hemiparesis, cortical blindness, impaired hearing, behavioral abnormalities, and cognitive deficits (impaired learning, reasoning, dexterity, memory, perception, etc.). Some sequelae, such as epilepsy, may persist long-term [Summer et al., 2005].

In cases with impaired consciousness, a lumbar puncture should be performed to assess for concurrent meningitis. Caution, however, should be exercised due to the elevated intracranial pressure. CSF in cerebral malaria is clear, with protein ranging up to a high of 0.4 g/L (400 mg/dL); septic CSF is cloudy, with neutrophils comprising about 99 percent of leukocytes and protein ranging from approximately 1 to 3 g/L (1000–3000 mg/dL). Blood cultures to exclude bacteremia are indicated. The electroencephalogram (EEG) in children with cerebral malaria reveals nonspecific generalized slowing [Molyneux et al., 1989] and may be helpful in detection of subclinical seizures that might otherwise pass unnoticed [Maitland and Marsh, 2004]. Neuroimaging may also be abnormal. Acutely, MRI may demonstrate multifocal T2-enhancing lesions indicative of capillary occlusion and cerebral edema [Chia et al., 1992]. CT scan has been reported to demonstrate generalized and sulcal atrophy as a sequela of disease [Newton et al., 1994].

In countries where rising drug resistance is a concern, accurate diagnosis of malaria is deemed essential before prescribing antimalarial treatment, particularly the artemesinin-based therapies, which may also be less well tolerated and more expensive. The current gold standard for diagnosis of P. falciparum infection remains the study of thick and thin peripheral Giemsa-stained blood films. Giemsa microscopy is regarded as the most suitable diagnostic approach for malaria because it is inexpensive to perform and it is able to differentiate malarial species and quantify parasites. However, this technique requires well-trained, competent microscopists and rigorous maintenance of equipment and reagents. With the introduction of high-quality light-emitting diode (LED) illumination and solar battery chargers, microscopy has become more feasible in remote areas.

Close scrutiny is required to ensure accuracy in ascertaining the presence of small, ring-form trophozoites and crescent-shaped gametocyte [Coatney et al., 1971; Lowichik and Ruff, 1995]. In the hands of a skilled technician in field conditions, thick films can detect 1 infected cell in 1000 red blood cells (0.001 percent), or 50–100 parasites/μL of blood [Moody, 2002]. Erythrocytes containing Plasmodium ring stages are more likely to be found in peripheral blood because the mature stages undergoing intraerythrocytic replication become sequestered in brain and other deep areas of the body. Blood smears should be prepared at 8- to 12-hour intervals, until diagnosis can be made [Birbeck, 2004]. If antimalarial therapy was started before preparation of blood smears, the smears may be negative.

While examination of Giemsa-stained blood films remains the gold standard, the introduction of rapid diagnostic tests is rapidly changing recommended algorithms for diagnosis and treatment of malaria. These assays detect malaria antigen in a small (5–15 μL) amount of blood by immunochromatographic methodology with monoclonal antibodies directed against the target parasite antigen and impregnated on a test strip. They generally detect histidine-rich protein 2 (HRP-2) and lactate dehydrogenase isoenzymes, with the HRP-2 being specific for P. falciparum [Summer et al., 2005]. The result, usually a colored test line, is obtained in 5–20 minutes. These tests require no capital investment or electricity, and are simple to perform and easy to interpret. Most commonly used rapid diagnostic tests only detect P. falciparum, although some can also distinguish P. falciparum from other non-falciparum species. Depending on the parasite load, most rapid diagnostic tests have achieved greater than 95 percent sensitivity for P. falciparum, with less sensitivity for non-falciparum species [Wongsrichanalai et al., 2007]. Immunochromatography in the form of a dipstick kit has also been employed for Plasmodium detection [Moody, 2002]. Sensitive indirect fluorescent antibody and hemagglutination tests provide further diagnostic capability [Wilson et al., 1975]. [Moody, 2002] has reviewed testing for malarial parasites, with emphasis on methods capable of giving results in 1 hour or less.

Polymerase chain reaction is available mainly at reference and research laboratories. The chief advantage of molecular testing is a markedly increased sensivity, with the capability of detecting 5 parasites or fewer per μL of blood when parasites in peripheral blood samples are in low numbers. In addition, current polymerase chain reaction methods can distinguish between different species, offering less dependence on operator technique and skill.

In 2010, the World Health Organization published a revised version of evidence-based guidelines for the treatment of malaria [WHO, 2010]. The new guidelines emphasize the importance of parasitological confirmation of diagnosis in all patients suspected of having malaria before treating. Prompted in part by the increasing availability of rapid diagnostic tests, the move towards universal diagnostic testing of malaria is a critical step forward in the fight against malaria, as it will allow for the targeted use of artemesinin-based combination therapy for those who actually have malaria. This will help to reduce the emergence and spread of drug resistance. It will also help identify patients who do not have malaria, so that alternative diagnoses can be made and appropriate treatment provided [WHO, 2010].

Management

The mortality of untreated severe malaria (particularly cerebral malaria) is thought to approach 100 percent. With prompt, effective antimalarial treatment and supportive care, the mortality falls to 15–20 percent overall, although within the broad definition there are syndromes associated with mortality rates that are lower (e.g., severe anemia) and higher (metabolic acidosis). Death from severe malaria often occurs within hours of admission to hospital or clinic, so it is essential that therapeutic concentrations of a highly effective antimalarial are achieved as soon as possible. In this context, the main objective of the management of severe malaria is to prevent the patient from dying, with two considerations. One is treating an uncomplicated case of falciparum parasitemia, preventing it from developing into life-threatening, fulminant malaria. If the patient has already progressed to cerebral malaria, the second consideration goes beyond the use of antimalarial drugs and requires measures to treat deep coma, elevated intracranial pressure, hypovolemia, metabolic imbalance, anemia, convulsions, and other manifestations that accompany this often-fatal phase of the disease. Unfortunately, the available data on treatment efficacy are small, as most clinical trials on severe malaria management to date have been either negative, underpowered, or both, and only in 2005 were data produced that demonstrated an association between treatment intervention and decreased mortality.

As early as 1640, long before the etiologic agent was demonstrated, the therapeutic attributes of cinchona (quinine, quinidine) for treatment of malaria were recognized. In the 1950s, chloroquine became the mainstay of therapy, but efficacy was compromised in many parts of the world by the appearance of chloroquine-resistant strains of the parasite in Southeast Asia, Africa, and South America. Quinine returned to widespread use in the last decades of the 20th century. More recently, the development of artemisinin derivatives, the most rapidly acting of all antimalarial drugs, has transformed current treatment strategies. This Chinese medicinal herb, qinghao (Artemisia annua), also known as annual or sweet wormwood, has been used since antiquity to treat malaria. Recent efforts to understand its chemistry and pharmacology have been very positive. The plant yields a sesquiterpene compound called qinghaosu or artemisinin, which is active against Plasmodium. Artemisinin and its derivatives have been found to cure malaria with much less toxicity than quinoline antimalarials [Hien and White, 1993], and resistance to artemisinin has not yet been encountered. Artemisinin is also effective against the gametocyte stage in the bloodstream (the stage taken up by the mosquito), thereby reducing disease transmission in malaria-endemic areas. To lessen the chance of emergence of drug resistance further, artemisinin has been coupled with other differently acting drugs in artemisinin combination therapy [Adjuik et al., 2004]. Artemether (arthemeter), artesunate, and arteether are artemisinin derivatives that have been effective when used in combination with a second drug (e.g., artesunate-mefloquine) [Ashley, 2004; Olliaro and Taylor, 2004].

Randomized trials comparing artesunate and quinine from Southeast Asia show clear evidence of benefit with artesunate. In the largest multicenter trial, which enrolled 1461 patients (including 202 children below 15 years of age), mortality was reduced by 34.7 percent in the artesunate group when compared to the quinine group. The results of this and smaller trials are consistent and suggest that artesunate is the treatment of choice for adults with severe malaria. There are, however, still insufficient data for children, particularly from high-transmission settings, to enable us to draw the same conclusion. An individual patient data meta-analysis of trials comparing artemether and quinine showed no difference in mortality in African children. There is currently an on-going multicenter study comparing artesunate and quinine in the management of severe malaria in children in several African countries [Day and Dondorp, 2007].

The current World Health Organization treatment recommendations for severe (cerebral) malaria in children include rapid initiation of artesunate or quinine, given intravenously or intramuscularly. Oral artemisinin-based monotherapy is strongly discouraged because of concern about the development of resistant parasites. Parenteral antimalarials should be given for a minimum of 24 hours. Once the patient can tolerate oral therapy, it is essential to continue and complete treatment with an effective oral antimalarial using a full course of an effective ACT (artesunate plus amodiaquine or artemether plus lumefantrine or dihydroartemisinin plus piperaquine) or artesunate (plus clindamycin or doxycycline) or quinine (plus clindamycin or doxycycline). Where available, clindamycin should be substituted for doxycycline in children under the age of 8 years, given concerns in this age group for permanent yellowing or graying of the teeth and impairment of growth. Regimens containing mefloquine should be avoided in patients presenting initially with impaired consciousness because of an increased incidence of neuropsychiatric complications associated with mefloquine following cerebral malaria. The full World Health Organization recommendations are available at http://www.who.int/malaria/publications/atoz/9789241547925/en/index.html.

In the United States, the current CDC recommendations for treatment of cerebral malaria in children include rapid initiation of intravenous quinidine gluconate plus 7 days of doxycycline, tetracycline, or clindamycin, with switch to oral drugs as soon as the patient can tolerate oral medication. The artemisinin-based drugs remain available under investigational use only, and can be obtained by contacting the CDC directly at the CDC Malaria Hotline [(770) 488-7788 Monday–Friday 8 am to 4:30 pm EST; (770) 488-7100 after hours, weekends, and holidays]. Current CDC guidelines recommend that intravenous artesunate should be followed by atovaquone-proguanil (Malarone™), clindamycin, or mefloquine for 7 days. Both quinidine and quinine have narrow therapeutic ratios and should be infused slowly to avoid cardiovascular instability and hypotension. Because these agents can potentiate the hyperinsulinemic hypoglycemia seen in severe malaria, concurrent administration of a 5–10 percent dextrose solution is essential.

Supportive care

In cerebral malaria, the focus shifts from treating an infectious disease to dealing with a medical emergency. Fluid and electrolyte balance has to be restored or managed. This includes hypovolemia (remedied by hydration with saline), hypoglycemia (50 percent dextrose intravenously), hyponatremia and hypokalemia (hydration with saline), and renal failure (hemodialysis). Metabolic acidosis is a common complicaton of cerebral malaria and is strongly associated with a fatal outcome. Anemia occurs prominently in children. Hemodynamic shock and acute respiratory distress syndrome are also poor prognostic signs [Day and Dondorp, 2007]. Routine use of parental antibiotics is warranted because of the association between invasive bacterial infections and increased mortality.

In developed country settings, mechanical ventilation is often used in the unconscious cerebral malaria patient to protect the airway, although efficacy in prevention of mortality and sequelae has not been proven. Mannitol or glycerol can reduce intracranial pressure by creating an osmotic gradient across the blood–brain barrier and drawing fluid into the vascular system. In a small study of Kenyan children with cerebral malaria, mannitol was successful in reducing intracranial pressure for short periods, but no current data exist to support its routine use. Seizures can be treated with rectal diazepam, intravenous lorazepam, or other standard anticonvulsants, although prophylactic anticonvulsive therapy is not recommended because of concern for respiratory depression. Dexamethasone, used to relieve intracranial pressure, was found to be no better than a placebo in Thai patients (6–70 years); it prolongs coma, leads to complications, and is usually contraindicated [Warrell et al., 1982]. A meta-analysis combining results of the Thai study with a second malaria steroid trial in Indonesia concluded there was insufficient power to exclude a mortality effect either way. Exchange transfusion is also a popular adjunctive therapy utilized in well-resourced settings, with the goals of removal of parasitized erythrocytes, as well as cytokines and other soluble toxins, although no clear benefit has been proven in small studies. Nevertheless, some experts have suggested that exchange transfusion should be performed in any severely ill patient with a parasitemia that exceeds 15 percent or in any patient with parasitemia in the range of 5–15 percent with signs of poor prognosis [Summer et al., 2005]. Neither heparin nor dextran has been shown to be beneficial in reducing intracranial pressure by lowering blood viscosity [Newton and Krishna, 1998]. Similarly, studies of anti-tumor necrosis factor and iron chelators have not demonstrated clear benefit [Day and Dondorp, 2007].

Response to therapy should be monitored with blood smears that quantify parasite load. If parasite counts do not decrease by at least 75 percent within 48 hours of initiation of therapy, an alternative antimalarial agent should be selected.

Prevention

Prevention of malaria is challenging in resource-poor settings. Early efforts at vector control methods, with widespread use of insecticides and reduction of vector breeding sites (e.g., swamp drainage and environmental control with engineering methods for water source protection), were unsuccessful largely due to lack of resources, poor medical and public health infrastructure, and the emergence of resistance to insecticides. Since the 1990s, control efforts have focused more on prevention of mosquito bites through the use of insecticide-treated nets and on prompt recognition and effective treatment of malarial disease. Insecticide-treated nets have been shown to reduce child mortality in several large randomized controlled trials, with up to 33 percent reduction in mortality and 50 percent reduction in incidence of infections. Elimination of standing water near the household (e.g., in puddles, potted plant trays, old tires, urns, etc.) is also encouraged [Summer et al., 2005].

A vaccine for the prevention of malaria has yet to be realized, although several promising clinical trials are being conducted [Moorthy et al., 2004; Webster and Hill, 2003]. Development of an effective vaccine has been hampered by the presence of different stage-specific antigens displayed during the complex life cycle of the parasite. Of the 5300 genes present in the P. falciparum genome, approximately 4 percent are involved in immune evasion, including antigenic variation [Gardner et al., 2002]. Thus, it is likely that an effective vaccine will have to contain a combination of antigens able to protect against the infective sporozoite stage, the erythrocytic stage, and the transmissive gametocyte (sexual) stage. The role of antigenic variation in pathology of falciparum malaria has been reviewed by Kyes and associates [2001].

Clinical characteristics, clinical laboratory tests, and diagnosis

Clinical manifestations consist of a persistent fever, sweating, chills, myalgia, and mildly to moderately severe hemolytic anemia. Emotional depression has been reported, but severe neurologic symptoms are rare. Babesia in bovines can cause encephalitis, as does P. falciparum in humans. Parasitized red blood cells adhere to the endothelial lining of brain capillaries, thus evading destruction in the spleen [O’Connor et al., 1999; Wright et al., 1989].

Babesiosis should be suspected in patients who have spent time in tick-infested areas, had recent blood transfusions, or have undergone splenectomy [Homer et al., 2000]. The diagnosis is made by identification of the organism on thick and thin blood smears, but only if the parasitemia is high. In blood smears, the organism can be mistaken for the malaria parasite, but infected erythrocytes lack the malaria-characteristic hemozoin pigment (Figure 82-17). Inoculation of hamsters with suspect blood samples is useful in cases with low parasitemia but may require weeks for the disease to develop. However, the development of indirect fluorescent antibody assays and the polymerase chain reaction provide more sensitive detection of the parasitemia associated with babesiosis [Homer et al., 2000; Pruthi et al., 1995]. Serologic confirmation of infection has been determined in asymptomatic children [Ruebush et al., 1977]. Cross-reactivity with Plasmodium surface antigens has been reported [Gorenflot et al., 1998].

Fig. 82-17 Blood film showing human erythrocytes, some of which are infected with Babesia.

Although different in morphology, Babesia can be mistaken for Plasmodium in infected cells. The varied forms of the parasites can be seen. A, Ring forms. B, Ameboid shape. C, Tetrad configuration. Bar in micrograph represents 10 μm. (Giemsa stain.)

(Courtesy of Dr. Anne Kjemptrup. From Schuster FL. Cultivation of Babesia and Babesia-like blood parasites: agents of an emerging zoonotic disease. Clin Microbiol Rev 2002;15:365–373. Copyright © 2002, American Society of Microbiology.)

Management

Babesiosis was described in a neonate whose mother had been bitten by a tick 1 week before giving birth [Esernio-Jenssen et al., 1987]. Treatment with clindamycin and quinine was successful in effecting recovery. Two other cases of babesiosis in pregnancy were reported; in both, the pregnancies went to term and the infants were unaffected [Feder et al., 2003; Raucher et al., 1984].

Atovaquone (for pediatric patients 20 mg/kg twice a day for 7–10 days) plus azithromycin (12 mg/kg daily for 7–10 days) are the drugs of choice in treating babesiosis [Medical Letter, 2004], with clindamycin (20–40 mg/kg/day orally in three doses for 7 days) plus quinine (25 mg/kg/day orally in three doses for 7 days) as alternatives [Medical Letter, 2004]. Chloroquine therapy has been ineffective [Miller et al., 1978]. In seriously ill patients, exchange transfusion in combination with the above medications was reported to be efficacious, presumably by reducing the acute parasitic load [Doan-Wiggins, 1991]. [Homer et al., 2000] have prepared a comprehensive review of the organism and of the disease.

Epidemiology, microbiology, pathology

Chagas’ disease (American trypanosomiasis) is an important public health problem, affecting 15–16 million people in Latin America and extending from Argentina to the Mexican border with the United States [Pittella, 2009]. It is a disease of poverty, as the vector triatomine bug thrives in poor housing conditions (e.g., mud walls, thatched roofs), so in endemic countries, people living in rural areas are at greatest risk for acquiring infection.

The disease can also be passed by transplacental infection or through breastfeeding, though data to distinguish this route from intrauterine transmission are not available. Blood transfusions are another source of infection in endemic areas where the blood supply is not monitored for trypanosomes. The disease has also crossed into the United States, mostly in the southern tier, because of immigration from Latin America, where 8 percent of the population is seropositive. As a result, more than 50,000–100,000 people living in the United States have been infected [Kirchoff, 1993].

The vector, the triatomine bug or “kissing bug” (Triatoma spp.), lives in thatched walls and roofs of houses. Humans, cats, dogs, and other mammals serve as reservoirs from which the vector acquires the parasite. The parasite is found in the midgut and rectum of the insect. At the time the triatomine bug bites a human, it defecates on the skin surface, leaving a drop containing parasites. The parasite penetrates the broken skin when the presumptive host scratches or rubs the deposited fecal matter into the site of the insect bite, or when fecal matter is transferred by fingers on to the corneal surface of the eye or mucous membranes. Inside the host, the trypomastigotes invade cells near the site of inoculation, where they differentiate into intracellular amastigotes. The amastigotes multiply by binary fission and differentiate into trypomastigotes, and then are released into the circulation as bloodstream trypomastigotes. Trypomastigotes infect cells from a variety of tissues and transform into intracellular amastigotes in new infection sites, including in the CNS. Clinical manifestations, such as meningoencephalitis, can result from this infective cycle. The bloodstream trypomastigotes do not replicate (different from the African trypanosomes). Replication resumes only when the parasites enter another cell or are ingested by another vector. The “kissing bug” becomes infected by feeding on human or animal blood that contains circulating parasites. The ingested trypomastigotes transform into epimastigotes in the vector’s midgut. The parasites multiply and differentiate in the midgut and differentiate into infective metacyclic trypomastigotes in the hindgut [CDC website http://www.cdc.gov/chagas/epi.html].

Following remission of the acute symptoms, untreated T. cruzi infection can develop into a chronic form of the disease, which can manifest after an asymptomatic latent period. Without treatment, the chronic phase persists for a lifetime, and most remain asymptomatic. However, 15–30 percent of cases will develop symptomatic chronic disease, usually between the second and fourth decades of life. The symptoms of chronic Chagas’ disease result from long-term denervation of the autonomic nervous system, mostly affecting the cardiac and gastrointestinal systems [Pittella, 2009].

Clinical characteristics, clinical laboratory tests, and diagnosis

In endemic areas, T. cruzi infection is often acquired in childhood. Chagas’ disease in childhood can arise either as a result of congenital infection or after being bitten by the insect vector. Intrauterine Chagas’ disease occurs in 2–4 percent of infants born to mothers who have acute or chronic infection with T. cruzi [Lowichik and Ruff, 1995]. Such infants are usually born prematurely and are small for gestational age. Systemic symptoms are similar to other intrauterine infections and include jaundice, hepatosplenomegaly, edema, petechiae, and dysrhythmias. When meningoencephalitis occurs, seizures, hypotonia, and a weak suck are characteristically present [Bittencourt, 1976]. Almost half the infants who acquire infection in utero die by age 4 months.

When Chagas’ disease is acquired from an insect vector, it can manifest in two phases: acute and chronic. The acute phase begins about a week after infection, and is often asymptomatic, subclinical, and undiagnosed in 66–99 percent of cases, most of whom are babies or young children [Pittella, 2009]. The acute phase lasts a few weeks and is characterized by mild, nonspecific symptoms and signs (e.g., fever, vomiting, diarrhea, and hepatosplenomegaly). Inflammation develops at the portal of entry of the trypanosomes, producing a nodule (chagoma), and causing swelling of proximal lymph nodes. Romaña’s sign (unilateral palpebral and periocular swelling) may appear as a result of conjunctival contamination with the vector’s feces, and is a hallmark of the disease. A small percentage of acutely infected patients develop cardiac symptoms suggestive of myocarditis (e.g., dysrythmias) or signs of meningoencephalitis (e.g., generalized encephalopathy and seizures) [Pittella, 2009].

The neurologic manifestations mostly likely to be observed in children are a consequence of acute meningoencephalitis. The symptoms and signs are usually mild, occasionally with stupor or irritability, but can also present with seizures and focal neurologic signs. Almost all cases with CNS involvement will also have concurrent chagasic myocarditis. If it is untreated, the mortality rate following acute Chagas’ infection is approximately 5–10 percent and is usually related to heart failure and/or encephalitis [Pittella, 2009].

Following the latent asymptomatic phase of 10–25 years, chronic Chagas’ disease may re-present in young adulthood. Most symptoms are due to severe cardiac (cardiac arrhythmias, congestive heart failure, apical aneurysms, thromboembolisms) [Spina-Franca, 1996] or gastrointestinal (dysphagia and severe constipation leading to megaesophagus and megacolon) involvement. Reactivated chronic Chagas’ disease is also observed in immunosuppressed patients, most commonly those with AIDS (75–80 percent of cases), and less frequently in patients following organ transplant or with chronic use of immunosuppressive medications [Pittella, 2009; Cordova et al., 2008; Diazgranados et al., 2009].

In the child with acute meningoencephalitis due to Chagas’ disease, CSF reveals a mild to moderate pleocytosis (<100 cells/mm³), predominantly of lymphocytes, and protein elevation. Neuroimaging studies may reveal nonspecific ring-enhancing lesions seen with many CNS infections [Leiguarda et al., 1990]. No EEG abnormalities were seen in children with Chagas’ disease, although temporary irregularities appeared [Moya, 1994]. Sequence data on the T. cruzi genome are now available, which may lead to future attempts at intervention at specific genic targets [El-Sayed et al., 2005b].

The diagnosis of CNS Chagas’ disease is often made by direct examination of the CSF, which will reveal T. cruzi trypomastigotes. T. cruzi can be isolated from CSF in up to 75 percent of adult Chagas’ patients, but there is no evidence of overt CNS clinical symptoms [Cegielski and Durack, 1997]. Rarely, a fulminant meningoencephalitis will occur and be fatal. In a series of 11 children with CNS infection from Chagas’ disease, T. cruzi was isolated from the spinal fluid in 8 [Hoff et al., 1978]. Culture, direct microscopy, or histologic detection of T. cruzi in the blood or tissue obtained from brain biopsy are also likely to be positive. Serology is useful for diagnosis of neonatal Chagas’ disease but can also be misleading due to the presence of maternal antibodies in circulation. Positive serology in the absence of parasitemia and symptoms is probably due to antibody cross-reactivity [Pittella, 2009].

Brain biospy or autopsy will show edema, congestion, and scattered petechial hemorrhages. The fundamental histopathologic finding in encephalitis is multiple foci throughout the CNS, characterized by nodular arrangement of microglia, macrophages, neutrophils, and astrocytes, and mild perivascular lymphocytic infiltrate. T. cruzi are present in the form of amastigotes. Lymphocytic leptomeningitis is invariably present, and likely represents extension of the subadjacent cerebral inflammatory lesions [Pittella, 2009].

Management

Nifurtimox and benznidazole, which were introduced more than 30 years ago, are the only approved drugs with trypanocidal activity; they have limited effectiveness against chronic disease, are only available in oral formulation, and severe side effects can occur, including dose-dependent peripheral neuropathy in up to 25 percent of cases. Both drugs are only available in the United States by contacting the CDC.

Nifurtimox (for 1–10 years: 15–20 mg/kg/day in four doses for 90 days) is used for the treatment of Chagas’ disease [Medical Letter, 2004]. Benznidazole (for ages up to 12 years, 10 mg/kg/day in two doses for 30–90 days) is an alternative drug [Medical Letter, 2004]. Nifurtimox has been associated with a higher risk of chromosomal abnormalities, suggesting that alternative medications might be better. Allopurinol has been found to be as effective as nifurtimox or benznidazole in treating T. cruzi infection at a dose of 300 mg two or three times a day for 60 days [Gallerano et al., 1990].

The intracellular location of the parasite protects it from most drug therapies. Resistance to the basic drug therapy is a concern, and there is interest in finding or developing new drugs that are effective in treatment of Chagas’ disease. Itraconazole [McCabe et al., 1986] and ketoconazole [McCabe et al., 1987] were effective against T. cruzi in a mouse model of disease, but no trials have been conducted in humans. Ketoconazole, combined with benznidazole, demonstrated synergism when tested in the mouse model, but different strains of parasites exhibited variability in response to the drugs [Araújo et al., 2000]. Miltefosine (hexadecylphosphocholine), a phospholipid analog and anticancer drug that has been used with success in treatment of visceral leishmaniasis [Sundar et al., 2002], has been tested in vitro against intracellular stages of T. cruzi and has promise as an antimicrobial [Croft et al., 2003; de Castro et al., 2004]. Alkylphosphocholines, including miltefosine, in combination with ketoconazole, had in vitro activity against T. cruzi [Lira et al., 2001].

Epidemiology, microbiology, and pathology

Approximately 60 million people are at risk for infection [Kennedy, 2004]; most live in poverty and reside in remote rural regions [Rodgers, 2009]. Disease transmission occurs during activities such as farming, hunting, fishing, or washing clothes. The World Health Organization estimates that about 20–30 cases of Gambian sleeping sickness are diagnosed annually outside of Africa [Lejon et al., 2003a]. With increasing tourism to trypanosome-endemic regions of Africa, there is a greater likelihood that physicians outside of these areas will be seeing cases of sleeping sickness. Of the two types of sleeping sickness, the Gambian form is more likely to be encountered than the fulminant Rhodesian form because it can develop as a chronic disease [Lejon et al., 2003a]. Endemic geographic areas of the diseases do not overlap, which is helpful in distinguishing between the two types of trypanosomiasis. Cattle are an important reservoir for T. b. rhodesiense, although most wild animal species in game parks can harbor human pathogenic trypanosomes. For T. b. gambiense, humans are the main reservoir, with pigs and some wild animals possibly serving as a secondary reservoir [Brun et al., 2010].

Trypanosomes are transmitted by blood-feeding tsetse flies (genus Glossina) from one mammalian host to another. After feeding, the ingested trypanosomes undergo a number of biochemical and structural alterations in the fly’s midgut. Infective forms then reach the fly’s salivary glands, from where they are transmitted to the human host through biting. A fly remains infected for life.

Between 5 and 15 days after infection, a painful skin lesion (chancre) may develop at the site of the bite. The parasites spread in the bloodstream 1–3 weeks after the initial bite, invading lymph nodes, liver, spleen, heart, endocrine system, and eye (hemolymphatic stage). If infection is untreated, within a few weeks in the case of rhodesiense infection, or months in the case of gambiense infection, the parasites will cross the blood–brain barrier and enter the CNS (encephalitic stage). Subsequent complications include development of cerebral edema and petechiae. Obstruction of CSF flow may lead to ventricular dilatation. Cerebral and cerebellar atrophy may occur in the late stages of the disease. The spinal cord remains unaffected.

At postmortem examination, dural thickening and adhesion to surrounding structures are often present. The perivascular infiltrate in the gray and white matter is delineated so clearly that it has been called a gray sleeve. A mononuclear infiltrate is seen in the meninges and Virchow–Robin spaces during microscopic examination. Lymphocytes are more numerous than plasma cells. Endothelial proliferation of the capillaries may be present. The characteristic morular cell, a plasma cell with immunoglobulin M-containing inclusions (Russell bodies), was first reported by Mott [1906]. Differentiating the neuropathologic changes in African sleeping sickness from Chagas’ disease is practically impossible.

Tryptophol, the 3-indole ethanol formed by the parasite in trypanosomal sleeping sickness, produces the characteristic sleep [Cornford et al., 1979; Feldstein, 1973; Stibbs and Seed, 1973a; 1973b]. Because tryptophol also gains access to lymphoid tissues, such as spleen, thymus, and mesenteric lymph nodes, it may foster immunosuppression in sleeping sickness [Ackerman and Seed, 1976]. The trypanosome induces formation of antibodies to antigens on its surface called variable surface glycoproteins. The variable surface glycoproteins are under genic control and generate antigenic variation by activation and expression of a succession of variable surface glycoprotein genes – of which there are about 1000 in a genome containing 10,000 genes [Donelson, 2003]. Thus, host antibodies aimed at one set of surface antigens are soon rendered ineffectual by selection of bloodstream forms exhibiting newly synthesized surface glycoproteins. The recurring appearance in the bloodstream of trypanosomes with new surface antigens gives rise to periodic fluctuations in parasitemia. Development of a mechanism to modify or terminate this process appears necessary before control or eradication of this disease is feasible [Donelson and Turner, 1985]. Given the immunologic evasion conferred by antigenic switching, the availability of a vaccine in the near future appears unlikely. The trypanosome genome and, in particular, the phenomenon of antigenic variation has been reviewed by Donelson [2003]. Comparative information on trypanosomatid genomes is now available [El-Sayed et al., 2005a], as are sequence data on the T. brucei genome [Berriman et al., 2005].

Clinical characteristics, clinical laboratory tests, and diagnosis

The clinical presentation of trypanosomiasis can mimic malaria, syphilis, tuberculosis, toxoplasmosis, HIV, typhoid fever, borreliosis with neural involvement, mumps, and meningoencephalitis [Lejon et al., 2003b]. The typical symptoms and signs can be divided into two stages, although with T. b. rhodesiense infection there may be no clear distinction between the first and second stages.

Management

Suramin is recommended for patients who present with T. b. rhodesiense disease before the development of CNS disease. The drug is avoided in western and central Africa because, where Onchocerca spp. are also present, its high activity against these parasites can cause severe allergic reactions [Brun et al., 2010]. Pentamidine is the treatment of choice for first-stage disease caused by T. b. gambiense. In contrast, pentamidine treatment in intermediate-stage disease (defined as 10–20 white blood cells per μL CSF) does not appear to be effective, and is not generally recommended [Brun et al., 2010]. Pentamidine is reportedly less effective in treating rhodesiense than gambiense disease [Fairlamb, 2003]. Both drugs penetrate poorly across the blood–brain barrier into the CNS, making them ineffective in late-stage disease, and both have serious side effects. The following drugs and dosages are recommended for pediatric patients: for suramin, 20 mg/kg on days 1, 3, 7, 14, and 21; for pentamidine, 4 mg/kg/day intramuscularly for 10 days [Medical Letter, 2004].

A more recent alternative that is apparently less toxic and perhaps more effective is difluoromethylornithine (eflornithine) for both early- and late-stage disease [Doua and Boa Yapo, 1994; Fairlamb, 2003]. Difluoromethylornithine is not available in the United States but can be obtained through the World Health Organization [Medical Letter, 2004]. Recommended dosage is 400 mg/kg/day intravenously in four divided doses for 14 days [Fairlamb, 2003; Medical Letter, 2004]. Difluoromethylornithine is effective against the gambiense but not the rhodesiense form of the disease. Synergy has been found in combining suramin with eflornithine [Fairlamb, 2003].

In late stages of the disease, melarsoprol is recommended and is administered intravenously (for pediatric patients, the initial dose is 0.36 mg/kg, increasing to a maximum of 3.6 mg/kg at intervals of 1–5 days for a total of 9 or 10 doses, for a total of 18–25 mg/kg over 1 month) [Medical Letter, 2004]. The drug can cross the blood–brain barrier. It is effective against both forms of trypanosomiasis. However, adverse reactions are frequent and can be life-threatening. The most important reaction is an encephalopathic syndrome associated with increased intracranial pressure, which occurs in an average of 4.7 percent of T. b. gambiense and 8 percent of T. b. rhodesiense patients, with a case fatality rate of 44 percent and 57 percent respectively. Administration of corticosteroids (prednisolone) and diazepam can lessen the likelihood of post-treatment sequelae and prevent arsenical encephalopathy [Pepin et al., 1995]. Other serious side effects include seizures, psychosis and coma, skin reactions, and peripheral neuropathies. The clinician must be aware of the side effects of these drugs before therapy is initiated, and gradual increase in dosage is advised [Medical Letter, 2004; Seidel, 1985b]. Nifurtimox, used in treating Chagas’ disease, has also been employed in late-stage disease, when other late-stage antimicrobials are ineffective. After successful treatment, all patients need to be followed up with blood and CSF analysis at 6-month intervals for 2 years, after which the patient is considered cured. Detection of intrathecal IgM suggests treatment failure [Kennedy, 2008].