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Amebic intestinal infection is generally noninvasive and most often due to infection with Entamoeba histolytica. Extraintestinal spread can occur and usually involves the liver.
- Fecal–oral transmission
- Transmission also via contaminated water and food
- The incubation period is typically 1 to 3 weeks but can range from a few days to months or years.
- Amebiasis accounts for 40 to 50 million cases of colitis worldwide.
- 40,000 to 110,000 deaths annually
- The estimated prevalence in the United States is 4%, although there have been no recent serosurvey in developed countries.
- Many asymptomatic individuals with Entamoeba identified in their stool likely have Entamoeba dispar which is nonpathogenic but morphologically indistinguishable from E. histolytica.
- Worldwide distribution involving an estimated 10% or more of the world’s population
- Most common in tropical areas, with infection rates as high as 20–50%
- Highest morbidity and mortality are seen in developing countries in Central America, South America, Africa, and Asia.
- The very young, the elderly, and patients with underlying immunosuppression or malnutrition are at highest risk for severe disease.
- Patients in whom the diagnosis should be considered include the following:
- Immigrants from or travelers to endemic areas
- Children with bloody stools or mucus in stools
- Children with hepatic abscess
- The febrile child with right upper quadrant pain and tenderness, abdominal pain, or discomfort
- The child with hepatomegaly, typically without jaundice
- Treatment of drinking water
- Hand washing
- Appropriate disposal of human fecal waste
- Use of condoms
- Infection-control measures: Standard precautions are recommended for the hospitalized patient.
- E. histolytica is excreted as cysts or trophozoites in the stool of infected patients.
- Ingested cysts are unaffected by gastric acid and become trophozoites that colonize and invade the colon.
- Amebae attach to epithelial cells via a galactose/N-acetylgalactosamine (Gal/GalNac)–binding lectin
- The parasite has the ability to lyse human epithelial cells or kill by inducing apoptosis.
- Then cytokines and chemokines released attract neutrophils, macrophages, and lymphocytes. The host immune response contributes significantly to the reduction of epithelial integrity.
- Amebae then use cysteine protease to cleave extracellular matrix proteins to invade the submucosal layers.
- The EhCPDH112 complex interacts with mucosal tight junction proteins to produce mucosal damage.
- Amebae can then disseminate directly from the intestine to the liver in up to 10% of patients. Dissemination from the liver to the lung, heart, brain, and spleen has been described.
- E. histolytica is a nonflagellated protozoan parasite.
- Other species of the Entamoeba family are nonpathogenic, including the morphologically identical E. dispar.