Other Diagnostic Techniques for Entamoeba histolytica

The standard O & P examination is the recommended procedure. In very fresh specimens, mobile amoeba may be seen. The most important technique for recovering and identifying E. histolytica is the permanent stained smear (usually iron hematoxylin or trichrome). A minimum of three specimens over a period of ten days may be needed. Sigmoidoscopy specimens are often helpful for identifying these organisms as well.

A number of enzyme immunoassay (EIA) reagents are available. Some are able to differentiate the E. histolytica/dispar/moshkovski group from the non-pathogenic Entamoeba species. However, some kits available can screen for the major intestinal parasites found in the United States such as E. histolytica/dispar, Giardia duodenalis, and Cryptosporidium parvum. The image to the right shows an example.

Most kits require fresh or frozen stool; preservatives have been found to interfere with the detection.

Nucleic acid amplification methods are available for identification of E. histolytica/dispar, such as real time PCR and multiplex assays. They can detect and identify unique ribosomal ribonucleic acid or specific epitomal sequences. There are multiplex panels available that can detect a number of gastrointestinal pathogens as well, including pathogenic bacterial species, bacterial toxins, viral species along with E. histolytica, G. duodenalis, and Cryptosporidium.

A definitive diagnosis of E. histolytica should not be made without finding the organisms, so antibody methods are not very useful for gastrointestinal disease. However, they can be useful for extraintestinal disease. Examples are indirect fluorescent antibody and indirect hemagglutination tests. When interpreting results, it must be kept in mind that antibodies can persist 10 years or more.

Many states require reporting of pathogenic E. histolytica to public health facilities.