Practical Guidance for Clinical Microbiology Laboratories: Laboratory Diagnosis of Parasites from the Gastrointestinal Tract

Abstract

This Practical Guidance for Clinical Microbiology document on the laboratory diagnosis of parasites from the gastrointestinal tract provides practical information for the recovery and identification of relevant human parasites. The document is based on a comprehensive literature review and expert consensus on relevant diagnostic methods. However, it does not include didactic information on human parasite life cycles, organism morphology, clinical disease, pathogenesis, treatment, or epidemiology and prevention. As greater emphasis is placed on neglected tropical diseases, it becomes highly probable that patients with gastrointestinal parasitic infections will become more widely recognized in areas where parasites are endemic and not endemic. Generally, these methods are nonautomated and require extensive bench experience for accurate performance and interpretation.

Keywords: diagnosis; gastrointestinal; gastrointestinal infection; methods; parasites; parasitology.

FIG 1

Example of a case history form that can be used to guide clinician ordering for stool ova and parasite testing.

FIG 2

General life cycle of the trematodes. n.s., not shown. (Republished from reference with permission.)

FIG 3

Permanent-stain options for various organisms, identified from left to right. (First row) Wheatley's trichrome stains of a Giardia lamblia trophozoite, an Entamoeba histolytica trophozoite with ingested RBCs, an Entamoeba coli cyst with red chromatoidal bars, and a Chilomastix mesnili cyst; (second row) iron-hematoxylin stains of a Dientamoeba fragilis trophozoite, Giardia lamblia cysts, an Entamoeba coli cyst, and an Iodamoeba bütschlii cyst; (third row) modified acid-fast stains of large Cyclospora cayetanensis organisms (both stained and unstained), a medium-sized Cryptosporidium sp. (with small artifacts), large Cyclospora cayetanensis organisms (with medium-sized Cryptosporidium sp. cells and a small artifact) (note that not all Cyclospora oocysts stain with modified acid-fast stain), and Cryptosporidium sp. organisms (note the presence of sporozoites in some oocysts [not seen in Cyclospora]); (fourth row) an iron-hematoxylin–modified acid-fast combination stain of Giardia lamblia and Cryptosporidium sp., a modified acid-fast–modified trichrome–Ryan blue combination stain of Cystoisospora belli microsporidial spores, a modified trichrome–Ryan blue stain of microsporidial spores, a modified trichrome–Weber green stain of microsporidial spores; (fifth row) DFA stain of Cryptosporidium oocysts (apple green color), autofluorescence of Cyclospora cayetanensis oocysts, Calcofluor white staining of microsporidial spores (in the circle), and a combination modified acid-fast–modified trichrome stain of Cryptosporidium oocysts (pink) and microsporidial spores (in circle).

FIG A1

Morphological characteristics of nematode and cestode (helminth) eggs.

FIG A2

Diagnostic images showing the morphological characteristics of trematode eggs. ¹Paragonimus westermani is usually found in respiratory specimens; ²Schistosoma haematobium is usually passed in urine.