TABLE 47-1

Description of the More Common Groups of Human Parasites

TABLE 47-2

Body Sites and Parasite Recovery (Trophozoites, Cysts, Oocysts, Spores, Adults, Larvae, Eggs, Amastigotes, Trypomastigotes)

Note: This table does not include every possible parasite that can be found in a particular body site; the most likely organisms have been listed

^*Disseminated in severely immunosuppressed individuals.

TABLE 47-3

Specimens and/or Body Site: Specimen Options, Collection and Transport Methods, and Processing

Specimens and/or Body Site	Specimen Options	Collection and Transport Methods	Specimen Processing	Comments
Stool for ova and parasite (O&P) examination	Fresh stool	pint waxed container; 30 min if liquid, 60 min if semi formed, 24 h if formed; delivery to laboratory	Direct wet smear (not on formed specimen), concentration, permanent stained smear	Stool specimens containing barium are unacceptable; intestinal protozoa may be undetectable for 5 to 10 days after barium use. Certain substances and medications also impede detection of intestinal protozoa: mineral oil, bismuth, antibiotics, antimalarial agents, and nonabsorbable antidiarrheal preparations. After administration of any of these compounds, parasitic organisms may not be recovered for a week to several weeks. Specimen collection should be delayed after barium or antibiotics are administered for 5 to 10 days or at least 2 weeks, respectively.
	Preserved stool*	5% or 10% formalin, MIF, SAF, Schaudinn’s, PVA, modified PVA, single vial systems, universal fixative	Concentration, permanent stained smearDepending on specimen (fresh or preserved) and patient’s clinical history, immunoassays may also be performed.
Stool for culture of nematodes	Fresh stool, entire stool specimen	pint waxed container; immediate delivery to laboratory	Filter paper strip, Petri dish, agar plate, charcoal cultures are all available.	Fresh stool (do not refrigerate) is required for these procedures.
Stool for recovery of tapeworm scolex	Preserved stool, entire stool specimen	5% or 10% formalin (10% recommended)	The stool is filtered with a series of mesh screens and examined for the very small tapeworm scolex (proof of therapy efficacy) and/or proglottids (uncommon procedure but an option).	After treatment for tapeworm removal, the patient should be instructed to take a saline cathartic and to collect all stool material passed for the next 24 hr. The stool should be immediately placed in 10% formalin and thoroughly broken up and mixed with the preservative (1-gallon [3.8-liter] plastic jars are recommended, half full of 10% formalin).
	Adult worms, worm segments	Saline, 70% alcohol
Cellophane tape preparation for pinworms	Surface sample from perianal skin; anal impression smear	Cellulose (Scotch) tape preparation or commercial sampling paddle or swab	Tape is lifted from a slide, a drop of xylene substitute is added, the tape is replaced, and the specimen is ready for examination under the microscope.	Specimens should be collected late at night after the person has been asleep for several hours or first thing in the morning before going to the bathroom or taking a shower. At least 4 to 6 consecutive negative tapes are required to rule out the infection.
Sigmoid colon	Sigmoidoscopy material, prepared as smears	Fresh or PVA or Schaudinn’s smears; specimen is taken with a spatula rather than cotton-tipped swabs; transported as smears in preservative	Direct wet smear, permanent stained smears	Material from the mucosal surface should be aspirated or scraped; it should not be obtained with cotton-tipped swabs. At least six representative areas of the mucosa should be sampled and examined (six samples, six slides). A parasitology specimen tray (containing Schaudinn’s fixative, PVA, and 5% or 10% formalin) should be provided, or a trained technologist should be available at the time of sigmoidoscopy to prepare the slides. Examination of sigmoidoscopy specimens does not take the place of routine O&P examinations.If the amount of material is limited, use of a fixative containing PVA is highly recommended.
Duodenum	Duodenal contents	Entero-Test or aspirates; string in Petri dish or tube; immediate transport to laboratory	The specimen may be centrifuged (10 min at 500× g) and should be examined immediately as a wet mount for motile organisms. Iodine also can be used.Direct wet smear of mucus; permanent stained smears can also be prepared.	A fresh specimen is required; the amount may vary from < 0.5 mL to several milliliters of fluid. If the specimen cannot be completely examined within 2 hr after it is taken, any remaining material should be preserved in 5% to 10% formalin.
Entero-Test capsule (string)	Duodenal contents	Entero-Test (string test) in Petri dish (fresh) or preserved in PVA	Bile-stained mucus clinging to the yarn should be scraped off (mucus can also be removed by pulling the yarn between thumb and finger) and collected in a small Petri dish; disposable gloves are recommended. Usually 4 or 5 drops of material are obtained. The specimen should be examined immediately as a wet mount for motile organisms (iodine may be added later to facilitate identification of any organisms present). Organism motility is like that described previously for duodenal drainage. The pH of the terminal end of the yarn should be checked to ensure adequate passage into the duodenum (a very low pH means that it never left the stomach). The terminal end of the yarn should be yellow-green, indicating that it was in the duodenum (the bile duct drains into the intestine at this point).Permanent stained smears can also be prepared.	If the specimen cannot be completely examined within 1 hr after removal of the yarn, the material should be preserved in 5% to 10% formalin or PVA-mucus smears should be prepared.
Urogenital tract	Vaginal dischargeUrethral dischargeProstatic secretions	Saline swab, transport swab (no charcoal), culture medium, plastic envelope culture,air-dried smear for FA	Direct wet smear; fluorescence; urine must be centrifuged before examination.	Fresh specimens are required; an air-dried smear may be an option for fluorescence. Do not refrigerate swabs and/or culture containers at any time, because motility and/or ability to grow will probably be lost.
	Urine	Single unpreserved specimen, 24-hr unpreserved specimen, early morningNucleic acid-based testing media according to manufacturer’s instructions	Examination of urinary sediment may be indicated in certain filarial infections. Administration of the drug diethylcarbamazine (Hetrazan) has been reported to enhance the recovery of microfilariae from the urine. The triple-concentration technique is recommended for the recovery of microfilariae. The membrane filtration technique can also be used with urine for the recovery of microfilariae. A membrane filter technique for the recovery of Schistosoma haematobium eggs has also been useful.
Sputum	Sputum	True sputum (not saliva)	Direct wet smear; permanent stained smears; fluorescence also available (Calcofluor for microsporidia). Sputum is usually examined as a wet mount (saline or iodine), using low and high dry power (×100 and ×400). The specimen is not concentrated before preparation of the wet mount. If the sputum is thick, an equal amount of 3% sodium hydroxide (NaOH) (or undiluted chlorine bleach) can be added; the specimen is thoroughly mixed and then centrifuged. NaOH should not be used if the examiner is looking for Entamoeba spp. or Trichomonas tenax.After centrifugation, the supernatant fluid is discarded, and the sediment can be examined as a wet mount with saline or iodine. If examination must be delayed for any reason, the sputum should be fixed in 5% or 10% formalin to preserve helminth eggs or larvae or in PVA fixative to be stained later for protozoa.	True sputum is required; all specimens, especially induced specimens and BAL, should be delivered immediately to the laboratory (do not refrigerate).
	Induced sputum	No preservative (10% formalin if time delay)
	Bronchoalveolar lavage (BAL)	Sterile; immediate delivery to laboratory
Aspirates	Bone marrow	Sterile; immediate delivery to laboratory	Permanent stained smears; cultures can also be set (specifically designed for the recovery of blood parasites).	All aspirates for culture must be collected using sterile conditions and containers; this is mandatory for culture isolation of leishmaniae and trypanosomes.
	Cutaneous ulcers	Sterile plus air-dried smears
	Liver, spleen	Sterile, collected in 4 separate aliquots (liver)
	Lung
	Transbronchial aspirate	Air-dried smears
	Tracheobronchial aspirate	Air-dried smears
Central nervous system	Cerebrospinal fluid (CSF)	Sterile	Direct wet smear, permanent stained smears; culture for free-living amebae (Naegleria, Acanthamoeba spp.).	All specimens must be transported immediately to the laboratory (STAT procedure).
Biopsy	Intestinal tract	Routine histology	Direct wet smears, permanent stained smears; specimens to histology for routine processing.	The more material that is collected and tested, the more likely the organism is to be isolated and subsequently identified. Sterile collection is required for all specimens that will be cultured; bacterial and/or fungal contamination prevents isolation of parasites in culture.
	Cutaneous ulcers	Sterile, nonsterile to histopathology(formalin acceptable)
	Eye	Sterile (in saline), nonsterile to histopathology
	Scrapings	Sterile (in saline)
	Cornea (scrapings)	Collected by physician, placed directly on microscope slide	Fixed using methyl alcohol and stained using Calcofluor white	Helpful in diagnosis of Acanthamoeba keratitis
	Liver, spleen	Sterile, nonsterile to histopathology
	Lung
	Brush biopsy	Air-dried smears
	Open lung biopsy	Air-dried smears
	Muscle	Fresh, squash preparation, nonsterile to histopathology
	Skin biopsy	Nonsterile to histopathology(formalin acceptable)
	Scrapings	Sterile (in saline), nonsterile to histopathology
	Skin snip	Aseptic, smear or vialNo preservative
Blood	Smears of whole blood	Fresh (first choice)Thick and thin films; immediate delivery to laboratory	Thick and thin films, specialized concentrations and/or screening methods	Examination of blood films (particularly for malaria) is considered a STAT procedure; immediate delivery to the laboratory is mandatory.
	Anticoagulated blood	Anticoagulant (second choice)EDTA* (first choice)Heparin (second choice)	Thick and thin films, specialized concentrations and/or rapid methodsQBC Microhematocrit Centrifugation Method (Becton Dickinson, Tropical Disease Diagnostics, Sparks, Maryland)	Delivery to the laboratory within 30 min or less; if this time frame is not met, typical parasite morphology may not be seen in blood collected using anticoagulants.Knott concentration procedure: Used primarily to detect microfilariae in the blood, especially when a light infection is suspected. The disadvantage of the procedure is that the microfilariae are killed by the formalin and therefore are not seen as motile organisms.Membrane filtration technique: This technique, using Nuclepore filters, has proved highly efficient in demonstrating filarial infections when microfilaremias are of low density. It has also been successfully used in field surveys.

^†EDTA, Ethylenediaminetetraacetic acid; FA, fluorescent antibody; MIF, merthiolate-iodine-formalin; PVA, polyvinyl alcohol; SAF, sodium acetate–acetic acid–formalin.

^*A number of new stool fixatives are available; some use a zinc sulfate base rather than mercuric chloride. Some collection vials can be used as a single-vial system; both the concentration and permanent stained smear can be performed from the preserved stool. However, not all single-vial systems (proprietary formulas) provide material that can be used for fecal immunoassay procedures. A universal fixative is now available (TOTAL-FIX), which contains no formalin, no mercury, and no PVA.

Modified from Garcia LS: Diagnostic medical parasitology, ed 5, Washington, DC, 2007, ASM Press.