Laboratory diagnosis of amebiasis

Abstract

The detection of Entamoeba histolytica, the causative agent of amebiasis, is an important goal of the clinical microbiology laboratory. To assess the scope of E. histolytica infection, it is necessary to utilize accurate diagnostic tools. As more is discovered about the molecular and cell biology of E. histolytica, there is great potential for further understanding the pathogenesis of amebiasis. Molecular biology-based diagnosis may become the technique of choice in the future because establishment of these protozoa in culture is still not a routine clinical laboratory process. In all cases, combination of serologic tests with detection of the parasite (by antigen detection or PCR) offers the best approach to diagnosis, while PCR techniques remain impractical in many developing country settings. The detection of amebic markers in serum in patients with amebic colitis and liver abscess appears promising but is still only a research tool. On the other hand, stool antigen detection tests offer a practical, sensitive, and specific way for the clinical laboratory to detect intestinal E. histolytica. All the current tests suffer from the fact that the antigens detected are denatured by fixation of the stool specimen, limiting testing to fresh or frozen samples.

FIG. 1.

Drawing of intestinal Entamoeba spp. showing morphological features. All illustrations are adapted from various sources.

FIG. 2.

Algorithm of intestinal amebiasis.

FIG. 3.

Practical algorithm for diagnosis of patients with amebic liver abscess.