Description

• Second leading parasitic cause of death worldwide behind malaria
• Infects or colonizes up to 10% of world’s population—especially in developing countries
• Travelers to and immigrants from endemic regions, persons engaging in anal intercourse, and immunocompromised individuals at highest risk
• Fecal–oral transmission—ingestion of parasite cysts
• 90% of infected patients are either asymptomatic or have minimal symptoms.

Geriatric Considerations
Higher incidence of complications, including toxic megacolon (1)

Pediatric Considerations
Neonates tend to present with severe dehydration.

Pregnancy Considerations
No documented cases of placental involvement or vertical transmission. Pregnant women who contract amebic colitis are at higher risk for fulminant infection.

Epidemiology

Incidence varies by region and socioeconomic status.

• ~40 to 50 million symptomatic cases worldwide annually; 100,000 deaths; 2–4% of worldwide diarrheal cases
• 4–10% of those infected with E. histolytica develop amebic colitis; <1% develop amebic liver abscess.
• Endemic in Africa, Central and South America, India and Asia
• In United States—3,000 cases seen annually—mostly from immigrants from and travelers to endemic regions
• Amebic colitis affects patients of all ages and genders.
• Invasive amebiasis (liver abscess, peritonitis, colonic perforation) affects men > women (3:1).
• Liver abscess affects adults > children (10:1).
• Very young children predisposed to fulminant colitis

Prevalence

• U.S. prevalence—~ 4%
• 10% of world’s population is infected.
• Asymptomatic Entamoeba dispar is 10 times more common than E. histolytica.
• Entamoeba infection rates up to 50% in areas of Central and South America, Africa, India, and Asia.
• Seroprevalence of E. histolytica in asymptomatic persons in developing countries 1–21%

Etiology and Pathophysiology

• Infection results from ingestion of E. histolytica cysts in contaminated food or water.
• Cyst form is infectious, environmentally stable, and resistant to chlorination.
• Trophozoites are responsible for colonic tissue invasion and destruction. Trophozoites attach to colonic epithelial cells by galactose and N-acetyl-D-galactosamine-specific lectin, activating lytic and apoptotic pathways leading to mucosal inflammation.
• Extraintestinal disease results from hepatobiliary and/or hematogenous spread.
• Passive and active immunity via mucosal immunoglobulin A (IgA) response

Risk Factors

• Poor sanitary conditions
• Low socioeconomic status
• Institutional living
• Men who have sex with men (MSM)
• Immunocompromised state associated with increased disease severity and mortality
• Invasive disease is more common in certain locations, including Mexico, South Africa, and India (1).

General Prevention

• Improve public sanitation and personal hygiene to mitigate fecal–oral spread.
• Individuals traveling to endemic areas should adhere to proper food and water safety precautions.
• Amebic cysts are not killed by soap or low concentration of chlorine or iodine. Water should be boiled for >1 minute and uncooked vegetables washed with a detergent soap or soaked in acetic acid or vinegar for 10 to 15 minutes before consumption.
• Avoid anal and oral sex.
• Treat close contacts (reinfection is common).
• Amebiasis infection does not confer lifelong immunity.
• No prophylactic drug or vaccine is yet available to reduce infection and/or invasive disease.