Chapter 33 Parasitic infestations
1. Where and how does one acquire cutaneous parasitic diseases?
Parasitic skin diseases may arise from systemic spread or direct penetration of the skin. Cutaneous parasitic infestations are a major source of morbidity, affecting millions worldwide. Tropical climates, crowding, poor nutrition, sanitation problems, and limited medical resources are all associated with increased variety and severity of parasitoses. Ecologically temperate climates and industrialized societies are also afflicted by significant parasitic infestations because of local vectors, distant vacations, and widespread travel to and from areas of endemic infection for business, political, humanitarian, or military purposes. Immunosuppression due to drugs or disease leads to cutaneous manifestations of parasitic diseases that may be caused by unusual organisms.
2. What is “creeping eruption”?
Properly known as cutaneous larva migrans, and popularly known as “sandworms,” creeping eruption occurs when the larva of dog and cat hookworms (Ancylostoma caninum and A. braziliense, respectively) penetrate intact, exposed skin and begin migrating through the epidermis. The most common location for the eruption is the sole of the foot, although other sites such as the buttocks, back, and thighs, which may have rested on contaminated sand, are susceptible. Lacking the enzymes necessary to penetrate and survive in the deeper dermis, the larvae wander a serpiginous route at a speed up to 3 cm/day. Clinically, the primary lesion is a pruritic, erythematous, serpiginous burrow (Fig. 33-1). Although the larvae usually die in 2 to 8 weeks, survival up to 22 months has been reported. Several cases of cutaneous larva migrans–related erythema multiforme have been reported.
3. How do you treat creeping eruption?
An older method was to freeze the leading point of the burrow. This sometimes produced significant tissue destruction and often missed the larva, which may be up to 2 cm ahead of the visible burrow. A classic treatment is 10% topical thiabendazole suspension applied four times a day for at least 2 days after the last sign of burrow activity; however, this medication is not always readily available. This regimen has a high cure rate and minimal toxicity. Rare cases may require oral thiabendazole. Oral ivermectin, indicated for the treatment of larval currens, may have a role in the treatment of this disease as an off-label use.
4. What is different about larva currens?
Larva currens, or “racing larva,” is caused by Strongyloides stercoralis, a nematode with a normal life cycle similar to the hookworm. Strongyloides, however, is unique in that it can complete its life cycle within the human host and bypass the obligate soil phase of the hookworms. Autoinfection may occur to a point of overwhelming infestation and host death, especially in immunocompromised victims. The serpentine eruption of larva currens appears much the same as creeping eruption but is more likely to occur on the thighs, buttocks, or perineum due to larval penetration from the nearby colon. The eruption is more fleeting and lasts no more than a few days, during which the larva’s migratory speed through the dermis may be clocked at up to 10 cm/hr (Fig. 33-2). A nonspecific rash or hives may also occur because of hypersensitivity to the parasite.
5. Are there other nematode infestations that cause skin disease?
Enterobius vermicularis (pinworms) may cause a noisome perianal itch, but secondary complications including dermatitis, bacterial infections, and local abscesses can develop. Treatment is a single dose of mebendazole. Trichinella spiralis, which is acquired by eating undercooked pork, may cause a diffuse rash, nail bed splinter hemorrhages, and a subtle but persistent periorbital edema (trichinosis).
7. Where is onchocerciasis most prevalent? How is it transmitted?
Onchocerciasis, a disease produced by the tissue nematode Onchocerca volvulus, affects millions of people in Africa and Central and South America. The infective larval forms are transmitted to humans through the bite of the black fly (Simulium) (Fig. 33-3). The common term for onchocerciasis, river blindness, takes its name from its feared complication and the fast-flowing rivers where the parasite and vectors are found.
Figure 33-2. Larva currens. Biopsy demonstrates migrating larva of Strongyloides stercoralis in the dermis.
(Courtesy of the Fitzsimons Army Medical Center teaching files.)
Table 33-1. Parasitic Infestations of the Skin
| PARASITIC INFESTATION | VECTOR OR MODE OF TRANSMISSION |
|---|---|
| Filariasis | Mosquito |
| Onchocerciasis | Black fly |
| Creeping eruption | Soil contact and larval penetration |
| African trypanosomiasis | Tsetse fly |
| American trypanosomiasis | Kissing bug |
| Leishmaniasis | Sand fly |
| Schistosomiasis | Water contact and cercarial penetration |
| Dracunculiasis, sparganosis | Ingestion of larva |
| Echinococcosis, cysticercosis | Ingestion of cysts |
| Amebiasis | Direct contact or ingestion of cysts |
| Loiasis | Horse and deer flies |
| Demodex | Person-to-person contact in childhood |
8. Does river blindness cause cutaneous manifestations?
As the larval forms of Onchocerca develop into adult worms at the site of the bite, they produce subcutaneous nodules called onchocercomas, where numerous microfilariae are produced. They migrate into the skin, inducing a secondary dermatitis, skin pigmentation changes, skin thickening, frank elephantiasis, and an often disabling itching. The microfilariae also may migrate into the tissue of the eye and produce blindness due to severe uveal and corneal inflammation.
9. What are some of the problems with onchocerciasis treatment?
Diethylcarbamazine is effective treatment for the microfilarial stage, but a hypersensitivity reaction to large numbers of dying parasites in the anterior chamber of the eye may cause irreversible blindness and, in some cases, death. A safer course, in otherwise asymptomatic victims, is periodic “nodulectomy,” which removes the adult worms and significantly lowers the morbidity of onchocerciasis.
10. What is loiasis?
Loiasis, an infection endemic in the jungles of west and central Africa, is produced by the adult form of the tissue nematode, Loa loa, which is transmitted through the bite of various flies including deer flies (Chrysops species). Usually asymptomatic, this filarial disease may cause large areas of transient edema (Calabar swelling) as the worm migrates, and it may even migrate visibly across the conjunctiva. Subcutaneous nodules may also be seen in this disease, but the worm’s unique migration habits lead to the common name “eyeworm.”
11. What causes elephantiasis?
The term elephantiasis is applied to many dermatologic conditions that ultimately result in severe lymphatic obstruction and stasis. The affected limb may become massively enlarged, initially with pitting edema but later with a woodlike induration. The skin becomes discolored, and patches of warty growths may eventually cover the entire affected area. Lymphangitis and mechanical obstruction from lymphatic filariasis is but one way of causing elephantiasis. Offending organisms include Wuchereria bancrofti, Brugia malayi, and B. timori. The Brugia species cause elephantiasis of the extremities most commonly, while Wuchereria is notorious for genital disease that may eventuate in massive scrotal enlargement (Fig. 33-4).
12. Can other filarial diseases affect the skin?
Dirofilaria tenuis, the raccoon heartworm, can cause subcutaneous nodules. Dracunculus medinensis, or guinea worm, wanders through the subcutaneous tissue as part of its life cycle and eventually settles down where it may cause nodules and ulceration. Ivermectin, with or without coadministration of albendazole, has been used in many of the filarial diseases described previously. Dosages range from 200 to 400 mg/kg. The native treatment for Dracunculus is to snare the worm (up to 120 cm long in the female worm) through the skin and roll it up on a stick (the matchstick technique). Some medical historians believe that the caduceus (Fig. 33-5A), the symbol for a physician, has its origins from the ancient method of extracting the Dracuncula worm with a stick (Fig. 33-5B).
13. What is myiasis?
Myiasis is a disease in which various species of flies lay their eggs on or in human skin. When laid in an open wound, such as a chronic leg or decubitus ulcer, the eggs hatch into larvae (maggots) that feed on damaged skin and complete their life cycle. This is called “wound myiasis” and causes mild to severe inflammation, depending upon the fly species and wound location. In other cases, maggot nibbling of ulcer debris may actually dramatically improve the wound, and wound myiasis has been intentionally induced for this purpose.
14. What is a warble?
More properly called furuncular myiasis in humans, a warble occurs when fly eggs or larvae are introduced into intact skin. A large larva, more than 1 cm in length in some species, grows over time. Careful examination usually reveals a “snorkel” protruding through the skin of a boil that moves when the abscess is manipulated. Surgical extirpation is the treatment of choice, although other therapies, including occlusion of the furuncle opening with petrolatum or a piece of meat, have been reported to be successful (Fig. 33-6).
15. What is Congo floor maggot?
Unlike other forms of myiasis in which the larva feeds and pupates within the host tissue, the Congo floor maggot (Auchmeromyia luteola) lives in the soil or in the earthen floors of huts and crawls upon the host in the night for a blood meal. The larva, which may grow up to 18 mm long, requires 6 to 20 feedings before it pupates in the dirt. They carry no disease and may be avoided by sleeping on a raised bed.
16. What is tungiasis?
The sand flea, Tunga penetrans, can burrow into the foot where the female lays eggs, causing painful abscesses. Treatment is best accomplished by killing the female with chloroform or surgical excision. While late lesions will spontaneously ulcerate, potential complications include secondary infection and tetanus.
18. Do chiggers burrow into the skin to lay eggs like the sand flea?
They usually do not burrow beneath the skin, but the larval forms attach via their mouth parts (adults do not bite) and feed on tissue juices and lymph. They may feed for a few days if not removed, although the intense itching usually starts within a few hours after attachment. They prefer to feed in areas where the clothing is found in close contact with the skin, such as under socks and belts (Fig. 33-7). In some parts of Asia, they are a vector of scrub typhus and may be discouraged from attachment by wearing proper clothing, permethrin repellents, and by washing in hot, soapy water.
19. What is leishmaniasis?
Leishmaniasis, also known as Baghdad boil, kala-azar, espundia, oriental sore, and a variety of other colorful terms, is caused by Leishmania species, a protozoan parasite with a multicontinental distribution. Biting sand flies (Phlebotomus species) spread the disease between humans and a large variety of wild and domestic animal reservoirs. Several species and subspecies of Leishmania may produce infection, and the clinical manifestations and disease severity are generally species specific. Most forms cause nodules and chronic ulcerations of the skin that can spread lymphatically and lead to widespread cutaneous disease (Fig. 33-8).
Figure 33-4. Marked scrotal enlargement in elephantiasis.
(From Zaiman H, Jong EC: Parasitic diseases of the skin and soft tissue. In Stevens DL, editor: Atlas of infectious diseases, vol II, New York, 1995, Churchill Livingstone.)
Figure 33-5. A, Caduceus. B, The classic matchstick recovery technique used in extracting the adult female worm.
(From Zaiman H, Jong EC: Parasitic diseases of the skin and soft tissue. In Stevens DL, editor: Atlas of infectious diseases, vol. II, New York, 1995, Churchill Livingstone.)
21. Can leishmaniasis be contracted in the United States?
While most cases of leishmaniasis seen in the U.S. are acquired elsewhere, a form of cutaneous disease caused by L. mexicana may be acquired in central Texas and has been nicknamed “Highway 90 disease” by those familiar with its distribution. The standard treatment for leishmaniasis includes antimonial medications, but other medications such as ketoconazole, fluconazole, and physical modalities such as hyperthermia have anecdotally been shown to improve the lesions.
| SPECIES | DISEASE | DISTRIBUTION |
|---|---|---|
| L. donovani group | Visceral leishmaniasis, kala-azar | India, Asia, Middle East, Africa |
| L. tropica group | Old World cutaneous leishmaniasis, oriental sore, newly discovered viscerotropic disease | India, Middle East |
| L. viannia group (L. braziliensis group) | New World mucocutaneous leishmaniasis, espundia | Latin America |
| L. mexicana group | American cutaneous leishmaniasis | Mexico, Central America, Texas, South America |
22. How does cutaneous amebiasis, due to Entamoeba histolytica, present?
Usually the result of direct extension from hepatic or colorectal disease, cutaneous amebiasis presents with serpiginous, warty ulcers of the anogenital area called amebomas. These ulcers may produce extensive tissue loss and predispose to severe secondary bacterial infections. Less common presentations include infection by direct inoculation of the perineum in dysenteric infants wearing diapers and on the penis following anal intercourse with an infected person.
23. What are the skin findings in American trypanosomiasis?
American trypanosomiasis, or Chagas’ disease, is caused by the parasite Trypanosoma cruzi, which is introduced through the conjunctiva or skin following the bite of blood-sucking reduviid bugs (kissing bugs). This insect has the disgusting habit of defecating on the skin following its human blood meal, and the infected feces are inoculated into the conjunctiva or wound. A unilateral conjunctivitis and lid edema (Romana’s sign) are usually the first clinical signs. Later, the patient may become systemically ill with various rashes and subcutaneous nodules, as well as cardiac and gastrointestinal lesions that may be fatal.
24. What are the skin findings in African trypanosomiasis?
African trypanosomiasis, also called sleeping sickness, is due to Trypanosoma gambiense or T. rhodesiense. It may present with a trypanosomal chancre (primary cutaneous African trypanosomiasis) at the site of the bite, followed by nodules and dermatitis (secondary cutaneous African trypanosomiasis) (Fig. 33-9). The cardiac and neurologic complications of both forms of trypanosomiasis are the most serious clinical concerns.
25. Describe the cutaneous manifestations of schistosomiasis as they relate to the parasite’s life cycle.
Schistosomiasis is a trematode (fluke) infection produced by one of three species of the genus Schistosoma. Schistosomes have a complex life cycle that involves development in freshwater snails (intermediate host) and the release of free-swimming cercariae that penetrate the human skin. Penetration produces a transient pruritus and burning followed by blisters, bruising, and crusted papules over the next few days. As the worm reaches maturity in the portal or caval venous system, the ova are released by the adult female and passed into the feces or urine. Some ova are deposited in the skin and may produce nodules, ulcers, and warty tumors. The anogenital region is most often involved through direct extension from the bladder or rectum, but spread through the bloodstream and lymphatics may produce lesions at other sites.
26. Are swimmer’s itch and sea bather’s eruption the same thing?
No. Swimmer’s itch, also called clam digger’s itch and bather’s itch, is caused by the penetration of the skin by schistosome cercariae that normally infest birds. When first exposed, the victim will have a prickly eruption within a few minutes of cercarial penetration that rapidly resolves. Repeated exposure with an allergic response leads to larger, longer-lasting, and more pruritic papules that may cause pustules, blisters, and dermatitis. As with creeping eruption, the parasite cannot complete its life cycle because it cannot penetrate the epidermis.
27. What is sparganosis?
Sparganosis is an infection produced by various species of the tapeworm Spirometra, which is seen most commonly in Asia and Southeast Asia. Sparganosis is typically acquired by drinking water containing infected copepods or the ingestion of inadequately cooked snake or frog meat. Clinically, it presents as pruritic or painful nodules that contain the encysted tapeworm. “Application sparganosis” occurs when an eye or ulcer is contaminated by a poultice made from these same animals and is characterized by similar nodules at the site of inoculation (Fig. 33-10). Sparganosis is best treated by surgical removal of the tapeworm.
28. Can other tapeworms affect the skin?
Taenia solium (pork tapeworm) may produce cysticercosis cutis, which is acquired from the oral ingestion of eggs, usually due to poor sanitary habits. Clinically, it presents as painless subcutaneous nodules containing the larval stage of the tapeworm. Echinococcus granulosus, a dog tapeworm, produces fluctuant, cystic tumors in the skin (hydatid disease) as well as generalized hives and itching. It is acquired from the ingestion of contaminated food or water.
30. Does Demodex cause skin disease?
The role of Demodex in facial eruptions, particularly rosacea, has been a topic of debate for decades. Many convincing reports describe a recalcitrant folliculitis, often seen in immunosuppressed patients, which responds to mite-killing topical therapy. The contribution of Demodex to garden-variety rosacea is less certain, although patients with refractory rosacea pattern erythema and nodules have responded to miticidal therapy.
Key Points: Parasitic Infestations
2. Because of international travel and global conflict, what were once considered exclusively tropical diseases may show up in a North American clinic.
31. What are morgellons?
There are those who believe that many, if not most, patients diagnosed with delusions of parasitosis actually have infestations with small parasites known as morgellons. Complaining of stinging or biting sensations, patients will present with fibers and serum crusts, claiming that these are the creatures that exited the skin. Most reported victims live in California, central Texas, and Florida. Those who believe that morgellons are an unrecognized and underdiagnosed health threat have at various times linked them with latent Lyme disease, biologic contamination from meteorites, and clandestine bioweapons gone awry. Treatment is difficult but usually involves prolonged courses of antibiotics and homeopathic therapies. Health care providers should be aware there are Websites showing images of plant and clothing fibers, mixed with scale crust, that are positively identified as “morgellons.” In addition, there are weblogs describing how ignorant physicians are ignoring their patients’ needs and suggesting where they can go for a sympathetic ear and what products they may buy to get a cure.
Centers for Disease Control (CDC): Unexplained dermopathy: http://www.cdc.gov/unexplaineddermopathy/. Accessed July 25, 2010.
