Entamoeba

Entamoeba is a genus of amoeboid protozoa in the phylum Amoebozoa. It includes several species that colonize the human gut, most notably Entamoeba histolytica, which is a major human pathogen, as well as nonpathogenic relatives such as Entamoeba dispar, Entamoeba moshkovskii, Entamoeba hartmanni, and Entamoeba coli. Morphologically similar, these species are distinguished by molecular methods or antigen testing rather than by appearance under the light microscope alone.

Most Entamoeba species inhabit the large intestine and exist as cysts and trophozoites. Transmission occurs primarily through the fecal–oral route when cysts are ingested in contaminated water or food. In the colon, trophozoites may remain in the lumen or invade the mucosa; some infections are asymptomatic, while others cause disease depending on the species and host factors.

Entamoeba histolytica is the clinically significant member of the genus, capable of causing amebic dysentery and invasive disease such as hepatic amebic abscess. Nonpathogenic species generally cause few or no symptoms, and distinguishing pathogenic from nonpathogenic infections requires specific laboratory testing.

Diagnosis typically relies on stool examination, but differentiation among Entamoeba species by microscopy is unreliable. Antigen detection assays and PCR-based methods improve accuracy. Imaging, particularly liver ultrasound or CT, may be used to evaluate extraintestinal disease.

Treatment depends on the presentation. Invasive disease is treated with a tissue amebicide (for example, metronidazole or tinidazole) followed by a luminal amebicide (such as paromomycin or iodoquinol) to eradicate cysts. Asymptomatic carriage is usually treated with a luminal agent. Prevention focuses on sanitation, safe water, and good hygiene.