Author(s): Jennifer Cope, Ibne Ali

Infectious Agent

The protozoan parasite Entamoeba histolytica, and possibly other Entamoeba spp., causes amebiasis.

Transmission

Transmission occurs through the fecal–oral route, either by eating or drinking fecally contaminated food or water or through person-to-person contact (e.g., diaper changing, sexual activity).

Epidemiology

Amebiasis is distributed worldwide, particularly in the tropics, most commonly in areas of poor sanitation. E. histolytica is a common diarrheal pathogen in returned travelers. Long-term travelers (duration >6 months) are much more likely than short-term travelers (duration <1 month) to develop E. histolytica infection. Recent immigrants and refugees from these areas also are at risk. Outbreaks among men who have sex with men have been reported. People at greater risk for severe disease are pregnant, immunocompromised, or receiving corticosteroids; severe disease has also been reported among people with diabetes and those who consume alcohol.

Clinical Presentation

Most patients have a gradual illness onset days or weeks after infection. Symptoms include cramps, bloody or watery diarrhea, and weight loss, which might last several weeks. Occasionally, the parasite will spread to other organs (extraintestinal amebiasis), most commonly the liver. Amebic liver abscesses can be asymptomatic, but most patients present with right upper quadrant abdominal pain, fever, and weight loss, usually in the absence of diarrhea. Men are at greater risk of developing amebic liver abscess than are women for reasons not fully understood.

Diagnosis

Microscopy does not distinguish between E. histolytica (known to be pathogenic), E. bangladeshi, E. dispar, and E. moshkovskii. Historically, E. dispar and E. moshkovskii have been considered nonpathogenic, but evidence is mounting that E. moshkovskii can cause illness; E. bangladeshi has only recently been identified, so its pathogenic potential is not well understood. ELISA or PCR are needed to confirm the diagnosis of E. histolytica. Additionally, serologic tests can help diagnose extraintestinal amebiasis.

The Free-Living and Intestinal Amebas (FLIA) laboratory of the Centers for Disease Control and Prevention (CDC) can make a specific diagnosis using a duplex real-time PCR capable of detecting and distinguishing E. histolytica and E. dispar in stool, liver aspirates, and tissue samples. See more information about this testing and the CDC point of contact; select test code CDC-10478 from the list.

The FLIA laboratory does not accept samples for routine screening purposes, and only accepts samples previously tested elsewhere but still requiring confirmatory testing. CDC requests that state public health officials assist clinical laboratories referring specimens for further testing, including providing information about testing, specimen submission forms, and shipping information.

Treatment

Treat patients with symptomatic intestinal infection and extraintestinal disease with metronidazole or tinidazole, then treat with iodoquinol or paromomycin. Also, treat asymptomatic patients infected with E. histolytica with iodoquinol or paromomycin, because they can infect others and because 4%–10% of asymptomatic patients develop disease within 1 year if untreated. In patients with large amebic liver abscesses (>5 cm in diameter), draining the abscess in addition to treating with metronidazole or tinidazole can aid in the early resolution of pain and tenderness.

Prevention

To reduce their risk for amebiasis, travelers should follow food and water precautions (see Sec. 2, Ch. 8, Food & Water Precautions), practice good hand hygiene, and avoid fecal exposure during sexual activity.

CDC website: Amebiasis