Amebiasis

Basics

Description

Amebic intestinal infection is generally noninvasive and most often due to infection with Entamoeba histolytica. Extraintestinal spread can occur and usually involves the liver.

Epidemiology

  • 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.

Incidence

  • Amebiasis accounts for 40 to 50 million cases of colitis worldwide.
  • 40,000 to 110,000 deaths annually

Prevalence

  • 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.

Risk Factors

  • 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

General Prevention

  • 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.

Pathophysiology

  • 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.

Etiology

  • E. histolytica is a nonflagellated protozoan parasite.
  • Other species of the Entamoeba family are nonpathogenic, including the morphologically identical E. dispar.

There's more to see -- the rest of this topic is available only to subscribers.

© 2000–2025 Unbound Medicine, Inc. All rights reserved