Entamoeba histolytica infection

Entamoeba histolytica infection is also called amebic dysentery. Most infected patients have no symptoms but pass cysts in their feces. Other patients have mild diarrhea, severe colitis, or liver abscesses.

3,600 (US); 42,000,000 (Global)
Amoebiasis; Amebiasis; Amebic dysentery;
Usually 2 weeks to 1 month; May be several months or years; [CCDM]
1.) Most asymptomatic; 2.) Mild: intermittent diarrhea with bloody mucous; 3.) Severe colitis (more common in children): fever and chills with severe bloody diarrhea; 4.) Liver abscess; [Harrisons, p. 415]
Standard; "Person to person transmission is rare. Transmission in settings for the mentally challenged and in a family group has been reported. Use care when handling diapered infants and mentally challenged persons." [CDC 2007 Guideline for Isolation Precautions] Communicability lasts for as long as E. histolytica cysts are passed (months to years), but cysts are often not found in dysenteric stools and trophozoites are fragile. [CCDM, p. 4]
Most infected patients have no symptoms but pass cysts in their feces. Patients with amebic dysentery may have mild symptoms or high fever with abdominal cramping. Tender hepatomegaly is common, and patients may also have anemia, weight loss, and amebomas (tumor-like masses of the colon). The organisms may invade any organ, but liver abscesses are the most common complication. [Merck Manual, p. 1645] Patients with amebic dysentery have fever, diarrhea, and blood in the stools. Complications include amebomas, liver abscesses, and rarely, lung and brain abscesses. [CCDM, p. 3] Only a minority of patients with amebic dysentery have fever. [Cecil, p. 2109] Chronic amebic dysentery mimics idiopathic inflammatory bowel disease. [Cohen, p. 348] Patients with liver abscesses may have right-sided pleural effusions and typically do not have active colitis. Jaundice is rare. Patients with liver abscesses may have leukocytosis, mild anemia, and elevated alkaline phosphatase. [Harrison ID, p. 1064-5] May cause jaundice if bile ducts are compressed by abscess; [Cohen, p. 1135t] Cutaneous amebiasis is rare--nodules and ulcers of mucous membranes and perianal granulation tissue. [Guerrant, p. 963]

The laboratory may fail to detect pus in stool specimens because the trophozoites lyse leukocytes. Lactoferrin tests can detect inflammatory diarrhea in such cases when fecal leukocytes are absent. [PPID 7th Ed., p. 1345] In liver abscesses, leukocytosis and elevated transaminases and alkaline phosphatase are common. [Cohen, p. 1010t] The standard diagnostic approach is a combination of serology with microscopic exam of 3 stool specimens. Repeat serology in one week if first test negative and clinical suspicion high. Amebic liver abscesses are treated with antibiotics, and drainage is rarely needed. [Harrisons, p. 415] The different strains (E. histolytica, E. dispar, and E. moshkovskii) cannot be distinguished microscopically. New evidence suggests that E. moshkovskii may also be pathogenic. "More specific tests such as enzyme immunoassay or PCR are needed to confirm the diagnosis of E. histolytica." [CDC Travel, p. 170]

Incidence of infection is high in developing countries, travelers, recent immigrants, inmates of institutions, and men who have sex with men. Cysts are present in fecally contaminated water and food, and on hands. Cysts can survive for weeks in moist environments. [Harrisons, 18th Ed, p. 548] Positive serology surveys found rates of 8.4% for Mexico, 25% for urban slum dwellers in Fortaleza (Brazil), and 40% for preschool children living in Dhaka, Bangladesh. [Cecil, p. 2107] Families with poor sanitation are at increased risk for E. histolytica infection. Transmission occurs by ingestion of water or food contaminated with feces containing cysts, which are relatively resistant to chlorine water treatment. [CCDM, p. 4-5] 95% of liver abscesses in travelers occur within 5 months of leaving an endemic area. Men who have sex with men are at increased risk of acquiring infection. [Harrison ID, p. 1064-5]
Microscopic examination of fresh stool; Fecal antigen assays to detect amoeba and distinguish between E. histolytica and E. dispar; Serology positive in extraintestinal (95%) and intraintestinal (70%) disease; [CDC website]
Global; More prevalent in tropical areas with poor sanitation, and long-term travelers more likely to get infected; [CDC Travel]
  • >fever
  • G abdominal mass
  • G abdominal pain
  • G blood in stool
  • G constipation
  • G diarrhea
  • G fecal leukocytes
  • G hepatomegaly
  • G jaundice
  • G liver function test, abnormal
  • G nausea, vomiting
  • H anemia
  • H leukocytosis
  • N headache
  • N seizure
  • R chest pain
  • R cough
  • R dyspnea
  • S skin or subcutaneous nodule
  • S ulcer of skin
  • X cystic or cavitary lesions
  • X pleural effusions
  • *bowel obstruction
  • *brain abscess or lesion
  • *pericarditis
  • *weight loss




Ingestion, Swimming, Sexual Contact
Person-to-Person, Human Fecal-Oral, Eating Contaminated Food, Eating Contaminated Produce, Waterborne (Ingesting, Inhaling, or Swimming)
  • Ingest infectious agents in food/water
  • Swim in contaminated water (ingestion or inhalation)
  • Travel to endemic area
"Amebic liver abscess should be treated with chemotherapy; surgery is rarely indicated." [Cohen]
1. (US) Third most common parasitic infection after giardiasis and cryptosporidiosis (1.2 cases per 100,000); [PPID, p. 3279] 1.2 X 3000 (assuming a population of 300 million) = 3600;
2. (Global) After malaria, amebiasis is the second leading cause of death from parasites. [Cecil, p. 980] Estimated 34 to 50 million symptomatic cases and 100,000 deaths each year; [PPID, p. 3278]