Amebiasis is caused by Entamoeba histolytica, an intestinal protozoan found worldwide.

• After malaria and schistosomiasis, the 3rd-leading parasitic cause of death all over the world.
• Most common in developing countries, immigrants from or travelers to endemic regions, those who perform anal sex, and immunocompromised individuals
• Most infected patients are asymptomatic or have minimal GI symptoms (about 90%):
  • Severe infection (i.e., amebic colitis) can occur in very young patients, pregnant women, patients on steroid therapy, and malnourished individuals (1,2).
• Infection is spread by the feco–oral route and caused by the ingestion of E. histolytica cysts (infective form) in contaminated food (garden vegetables), fecally contaminated soil, or water. Then, excystation in the terminal ileum or colon to form highly motile trophozoites (invasive form). The trophozoites then encyst and are excreted in the feces or invade the intestinal mucosal barrier and spread hematogenously via the portal circulation to the liver or other distant organs. The excreted cysts reach the environment to complete the cycle.
• Amebiasis is primarily an infection of the colon, but extraintestinal (liver, kidney, bladder, skin, lung, brain, male or female genitalia) disease can occur. Amebic liver abscess is the most common complication of invasive amebiasis. It can develop during the acute attack or 1–3 months later.
• The genus Entamoeba contains many species, including E. histolytica, E. dispar, E. moshkovskii, E. polecki, E. coli, and E. hartmanni. Only E. histolytica has been clearly associated with disease; the others are considered nonpathogenic (3). E. dispar and E. moshkovskii are nonpathogenic strains that are morphologically identical to E. hystolytica. The previously counted asymptomatic infections by so-called nonpathogenic strains of E. histolytica are now evidenced to be due to E. dispar and E. moshkovskii. Latest availability of sensitive and specific antigen detection and polymerase chain reaction (PCR) can now recognize E. histolytica in stool from E. dispar and E. moshkovskii.
• System(s) affected: Gastrointestinal (GI); Nervous; Renal/Urologic; Reproductive; Skin/Exocrine
• Synonym(s): Amebic colitis; Amebic dysentery

ALERT
Geriatric Considerations
More severe in elderly

Pediatric Considerations
More severe in neonates

Pregnancy Considerations
More severe in pregnancy

• Infection can affect patients of all ages.
• Amebic colitis affects both sexes equally (1).
• Amebic liver abscess incidence greater in men than women for unknown reasons

ALERT
Pediatric Considerations
Very young children seem to be predisposed to fulminant colitis.

Prevalence

• US ~4%; 10% of the world’s population. Asymptomatic E. dispar infection is 10 times more common than E. histolytica infection.
• Entamoeba infection is as high as 50% in areas of Central and South America, Africa, and Asia. Prevalence rates of E. histolytica, in asymptomatic persons in developing countries range from 1–21%.

• Low socioeconomic status
• Institutional living
• Male homosexuality
• Immunocompromised
• Severe disease and increased mortality are common in pregnancy, corticosteroid treatment, malignancy, malnutrition, and alcoholism.
• Invasive disease is more common in certain geographic locations, including some parts of Mexico, South Africa, and India.

• Eradication of fecal contamination of food and water through improved sanitation, hygiene, and water treatment.
• Individuals traveling to endemic areas should be advised on proper food and water handling. Water should be boiled for more than 1 minute and uncooked vegetables washed with a detergent soap or soaked in acetic acid or vinegar for 10–15 minutes before consumption.
• Avoiding sexual practices that involve fecal–oral contact with potential contamination of infective cysts
• Treatment of patients and close contacts, since reinfection is common
• Amebiasis does not confer lifelong immunity; reinfection possible (4)

• Invasion to the colonic mucosa is mediated by a galactose/N-acetylgalactosamine (GAL/GalNAc)-specific lectin, able to activate lytic and apoptotic pathways, and direct inhibition of the complement system by the trophozoite (4).
• Extraintestinal disease can result from hepatobiliary and/or hematogenous spread.

Infection results from ingestion of E. histolytica cysts in contaminated food, water, or by direct fecal–oral transmission.