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  1. CDC - DPDx - Amebiasis › dpdx › amebiasis
    • Causal Agents
    • Life Cycle
    • Geographic Distribution

    Several protozoan species in the genus Entamoeba colonize humans, but not all of them are associated with disease. Entamoeba histolytica is well recognized as a pathogenic ameba, associated with intestinal and extraintestinal infections. Other morphologically-identical Entamoeba spp., including E. dispar, E. moshkovskii, and E. bangladeshi, are generally not associated with disease although investigations into pathogenic potential are ongoing. While the discussed species are morphologically-identical, E. histolytica may be observed with ingested red blood cells (erythrophagocytosis); E. dispar may occasionally be seen with ingested erythrocytes as well, although its capacity for erythrophagocytosis is much less than that of E. histolytica. Non-pathogenic amebae (e.g. Endolimax nana, Iodamoeba buetschlii, other Entamoeba species) are important because they may be confused with E. histolyticain diagnostic investigations.

    Cysts and trophozoites are passed in feces . Cysts are typically found in formed stool, whereas trophozoites are typically found in diarrheal stool. Infection with Entamoeba histolytica (and E.dispar) occurs via ingestion of mature cysts from fecally contaminated food, water, or hands. Exposure to infectious cysts and trophozoites in fecal matter during sexual contact may also occur. Excystation occurs in the small intestine and trophozoites are released, which migrate to the large intestine. Trophozoites may remain confined to the intestinal lumen (A: noninvasive infection) with individuals continuing to pass cysts in their stool (asymptomatic carriers). Trophozoites can invade the intestinal mucosa (B: intestinal disease), or blood vessels, reaching extraintestinal sites such as the liver, brain, and lungs (C: extraintestinal disease). Trophozoites multiply by binary fission and produce cysts , and both stages are passed in the feces . Cysts can survive days to weeks in the extern...

    Pathogenic Entamoeba species occur worldwide and are frequently recovered from fresh water contaminated with human feces. The majority of amebiasis cases occur in developing countries. In industrialized countries, risk groups include men who have sex with men, travelers, recent immigrants, immunocompromised persons, and institutionalized populations.

  2. Parasites - Amebiasis | Amebiasis | Parasites | CDC › parasites › amebiasis

    Amebiasis is a disease caused by the parasite Entamoeba histolytica. It can affect anyone, although it is more common in people who live in tropical areas with poor sanitary conditions. Diagnosis can be difficult because other parasites can look very similar to E. histolytica when seen under a microscope. Infected people do not always become sick.

  3. Amebiasis (Entamoeba histolytica) | CDC › conditions › amebiasis

    Access Amebiasis (Entamoeba histolytica) case definitions; uniform criteria used to define a disease for public health surveillance.

  4. General Information | Amebiasis | Parasites | CDC › parasites › amebiasis

    Jul 20, 2015 · Amebiasis is a disease caused by a one-celled parasite called Entamoeba histolytica. Who is at risk for amebiasis? How can I become infected with E. histolytica? What are the symptoms of amebiasis?

  5. Pathogen & Environment | Amebiasis | Parasites | CDC › parasites › amebiasis

    Entamoeba histolytica is well recognized as a pathogenic ameba, associated with intestinal and extraintestinal infections. The other species are important because they may be confused with E. histolytica in diagnostic investigations.

  6. Amebiasis (Entamoeba histolytica) | CDC › case-definitions › amebiasis-1990

    Clinical Description Infection of the large intestine by Entamoeba histolytica may result in an illness of variable severity ranging from mild, chronic diarrhea to fulminant dysentery. Infection also may be asymptomatic. Extraintestinal infection also can occur (e.g., hepatic abscess).

    • Transmission
    • Epidemiology
    • Clinical Presentation
    • Diagnosis
    • Treatment
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    • Bibliography

    Fecal–oral route, either by eating or drinking fecally contaminated food or water or person-to-person contact (such as by diaper changing or sexual activity).

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

    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. Occasionally, the parasite may spread to other organs (extraintestinal amebiasis), most commonly the liver. Amebic liver abscesses may be asymptomatic, but most patients present with fever, right upper quadrant abdominal pain, and weight loss, usually in the absence of diarrhea. Men are at higher risk of developing amebic liver abscess than are women for reasons not fully understood.

    Microscopy does not distinguish between E. histolytica (known to be pathogenic), E. bangladeshi, E. dispar, and E. moshkovskii. E. dispar and E. moshkovskii have historically been considered nonpathogenic, but evidence is mounting thatE. moshkovskii can cause illness; E. bangladeshi has only recently been identified, so its pathogenic potential is not well understood. More specific tests such as enzyme immunoassay or PCR are needed to confirm the diagnosis of E. histolytica. Additionally, serologic tests can help diagnose extraintestinal amebiasis. CDC’s Free-Living and Intestinal Amebas laboratory can make a specific diagnosis by using a duplex real-time PCR capable of detecting and distinguishing E. histolytica andE. dispar in stool and liver aspirate samples. More information about this testing and the CDC point of contact can be found at

    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. histolyticashould also be treated with iodoquinol or paromomycin, because they can infect others and because 4%–10% develop disease within a year if left untreated.

    Food and water precautions (see Chapter 2, Food & Water Precautions) and hand hygiene. Avoid fecal exposure during sexual activity. CDC website:

    Choudhuri G, Rangan M. Amebic infection in humans. Indian J Gastroenterol. 2012 Jul;31(4):153–62.
    Escolà-Vergé L, Arando M, Vall M, Rovira R, Espasa M, Sulleiro E, et al. Outbreak of intestinal amoebiasis among men who have sex with men, Barcelona (Spain), October 2017 and January 2017. Euro Su...
    Heredia RD, Fonseca JA, Lopez MC. Entamoeba moshkovskiiperspectives of a new agent to be considered in the diagnosis of amebiasis. Acta Trop. 2012 Sep;123(3):139–45.
    Lachish T, Wieder-Finesod A, Schwartz E. Amebic liver abscess in Israeli travelers: a retrospective study. Am J Trop Med Hyg. 2016 May 4;94(5):1015–19.
  7. CDC - DPDx - Amebiasis - Laboratory Diagnosis › dpdx › amebiasis

    Nov 29, 2013 · Centers for Disease Control and Prevention 1600 Clifton Road Atlanta, GA 30329-4027, USA 800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC–INFO A-Z Index for All CDC Topics

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