- Clinical science
Amebiasis is an infectious disease caused by the anaerobic protozoan Entamoeba histolytica. Transmission usually occurs via the fecal-oral route (e.g., via contaminated drinking water) when traveling in an endemic region. Depending on its manifestation, amebiasis is termed either intestinal or extraintestinal. After an incubation period of one to four weeks, symptoms such as loose stools with mucus and fresh blood in combination with painful defecation develop. In extraintestinal amebiasis, amebic abscesses (mostly a single liver abscess in the right lobe of the liver) may form, resulting in pain as well as a feeling of pressure in the right upper quadrant (RUQ). Important diagnostic steps include stool analysis and liver ultrasound to assess extraintestinal amebiasis. Treatment consists of paromomycin to destroy intestinal amebae and metronidazole for invasive disease. Image-guided needle aspiration may be indicated in cases involving complicated liver abscesses.
- Occurence: E. histolytica is very common in tropical and subtropical regions (e.g., Mexico; , Southeast Asia, India) and affects more than 50 million people worldwide. Amebic infection is relatively rare in the US.
- Men and especially immunocompromised individuals have a higher risk of developing liver abscesses.
Epidemiological data refers to the US, unless otherwise specified.
- Pathogen: Entamoeba histolytica, a protozoan
- Amebic cysts are excreted in stool and can contaminate drinking water or food
- Transmission may also occur through sexual contact.
- Infection typically occurs following travel to endemic regions such as the tropics and subtropics.
- Life cycle: ingestion of mature cysts → excystation in the small intestine → cysts divide into 4 and then 8 → noninvasive colonization of the colon by trophozoites (may lead to intestinal and extraintestinal disease) → trophozoites encyst → the cysts are excreted (along with trophozoites) → cysts are reingested by the same patient or spread to another individual.
- Cyst stage: Cysts are very resilient (even against gastric acid) and are able to survive outside the host for months.
- Vegetative stage: trophozoite formation
- Intestinal amebiasis: 1–4 weeks
- Extraintestinal amebiasis: a few weeks to several years
- Loose stools with mucus and bright red blood
- Painful defecation, tenesmus, abdominal pain, cramps, weight loss, and anorexia
- Fever in 10–30% of cases and possible systemic symptoms (e.g., fatigue)
- High risk of recurrence, e.g., through self-inoculation (hand to mouth)
- A chronic form is also possible, which is clinically similar to inflammatory bowel disease.
Always consider amebiasis when a patient presents with persistent diarrhea after traveling to a tropical or subtropical destination!
- Mostly acute onset of symptoms; subacute courses are rare
- In 95% of cases: amebic liver abscess, usually a solitary abscess in the right lobe
- In 5% of cases: abscesses in other organs (e.g., especially the lungs; in rare cases, the brain), with accompanying organ-specific symptoms
- Microscopic identification of cysts or trophozoites in fresh stool
- The following tests confirm the microscopic findings (important since E. histolytica and Entamoeba dispar are morphologically identical ):
- Stool microscopy is not sensitive; , especially in later phases, so at least three stool samples should be examined before reporting a negative result.
- Colonoscopy with biopsy: flask-shaped ulcers
- Serological antibody detection
- Aspiration of abscesses: shows brown fluid/pus (exudate resembles anchovy paste)
- In amebic hepatic abscess
E. histolytica Engulfs Erythrocytes.
- Asymptomatic intestinal amebiasis
- Symptomatic intestinal amebiasis and invasive extraintestinal amebiasis
- Aspiration: ultrasound or CT-guided puncture of complicated liver abscesses at risk for perforation
- Surgical drainage: should generally be avoided, but may be indicated for inaccessible abscesses or ruptured abscesses in combination with peritonitis
To ensure successful treatment, the patient's stool must be analyzed regularly!References:
- Fulminant or necrotizing colitis
- Toxic megacolon → colon rupture
- Fistula formation (e.g., rectovaginal)
- Secondary infection → pyogenic abscess
- Abscess rupture → peritonitis
- Dissemination, possibly resulting in a brain abscess
- Direct extension to the pericardium or pleura
We list the most important complications. The selection is not exhaustive.
- Unpeeled fruits or vegetables should not be consumed if there is a potential risk of contamination by Entamoeba histolytica cysts (e.g., endemic region with low hygiene standards).
- Even chlorinated water can contain high concentrations of amebae; therefore, water should be boiled before use.
The main principles of amebiasis prevention concern consumption of potentially contaminated food and water and can be summarized as follows: "Boil it, cook it, peel it, or forget it."References: