Entamoeba histolytica (Amebiasis) - Information for Clinicians
Type of infection
Entamoeba histolytica is a protozoal parasite.
Sources of infection
- Amebiasis occurs worldwide. In the US most infections are seen in travelers to developing countries, although it is a rare cause of traveler's diarrhea. Men who have sex with men may develop amebiasis.
- The usual source is ingestion of food or water contaminated with human feces.
- Entamoeba dispar is a nonpathogenic species but it may be difficult to discriminate from E. histolytica by microscopy.
- High levels for E. dispar can result in a positive molecular test for E. histolytica by the FilmArray.
Usual symptoms
- The incubation period is 2-4 weeks.
- The majority of infections are asymptomatic. Asymptomatic patients shedding E. histolytica can infect others.
- Common symptoms include loose stool and abdominal pain. Dysentery (blood and mucous in stool) is not always present in people with amebiasis.
Treatment
- Usual therapy for gastroenteritis and invasive disease is high dose metronidazole (35-50 mg/kg/day po div tid or 500-750 mg po tid for 7-10 days). Tinidazole is an alternative that may be better tolerated.
- A second agent is usually used to eliminate cyst carriage after treatment and is the preferred treatment for asymptomatic cyst passers. Alternatives include paromomycin (25-35 mg/kg/day po div tid for 7 days), diiodohydroxyquinoline, or dilanoxanide furoate.
Complications
- Fulminant colitis and toxic megacolon. Ulcers may be seen on colonscopy.
- Bowel necrosis and peritonitis can occur.
- Liver abscess.
- Brain abscess.
Comments
- Asymptomatic cyst passers should generally be treated.
- Emphasize good hand hygiene.
- Prevention of amebiasis involves safe selection of food and drink when traveling.
- Filter surface water (absolute 1 micron or less) and treating with chlorine, chlorine dioxide, or iodine.