Entamoeba histolytica is one of the most common parasitic infections worldwide, infecting about 50 million people and resulting in 40 000–100 000 deaths a year. A sample of returned travelers who sought health care from 2007 through 2011 at any of 53 international GeoSentinel-associated clinics showed that most people diagnosed with E. histolytica had traveled for tourism to India, Indonesia, Mexico, or Thailand, as opposed to visiting with friends and relatives or traveling for business. Nevertheless, cases of amebiasis are not restricted to these countries and are distributed worldwide, particularly in the tropics, most commonly in areas of poor sanitation.
Microscopy relies on identifying E. histolytica cysts and trophozoites. It is performed on fixed faecal smears stained with a permanent stain (iron haematoxylin or trichrome). Infection with E. histolytica cannot be diagnosed on the basis of morphological criteria alone. Historically, the presence of haematophagous trophozoites (trophozoites containing ingested red blood cells) was regarded as suggestive of E. histolytica infection.
For symptomatic intestinal infection and extraintestinal disease, treatment with metronidazole or tinidazole should be followed by treatment with iodoquinol or paromomycin. Asymptomatic patients infected with E. histolytica should also be treated with iodoquinol or paromomycin, because they can infect others and because 4%–10% develop disease within a year if left untreated. Most patients have a gradual illness onset days or weeks after infection. Symptoms include cramps, watery or bloody diarrhea, and weight loss and may last several weeks.