Detection of intestinal protozoa in the clinical laboratory

Abstract

Despite recent advances in diagnostic technology, microscopic examination of stool specimens remains central to the diagnosis of most pathogenic intestinal protozoa. Microscopy is, however, labor-intensive and requires a skilled technologist. New, highly sensitive diagnostic methods have been developed for protozoa endemic to developed countries, including Giardia lamblia (syn. G. intestinalis/G. duodenalis) and Cryptosporidium spp., using technologies that, if expanded, could effectively complement or even replace microscopic approaches. To date, the scope of such novel technologies is limited and may not include common protozoa such as Dientamoeba fragilis, Entamoeba histolytica, or Cyclospora cayetanensis. This minireview describes canonical approaches for the detection of pathogenic intestinal protozoa, while highlighting recent developments and FDA-approved tools for clinical diagnosis of common intestinal protozoa.

FIG 1

Key microscopic morphology of the enteropathogenic protozoa. Organisms are ordered from largest to smallest, based on average cell size. (A) Balantidium coli trophozoite unstained, wet mount. (B) Cystoisospora belli oocyst. (C, D, and F) Trophozoite forms are shown stained with trichrome for E. histolytica (C), D. fragilis (D), and B. hominis (F). (E) Cyst form of Giardia stained with trichrome. (G and H) Cyclospora cayetanensis oocyst (G) and Cryptosporidium spp. oocyst (H) after modified acid-fast staining.