Amoebiasis

Amoebiasis is an infection caused by the intestinal protozoan Entamoeba histolytica. The parasite exists as cysts in the environment and as trophozoites in human tissue. Infection occurs when a person ingests mature cysts in contaminated food or water, or via oral-anal contact. Cysts are hardy and can survive outside the host, enabling transmission in areas with poor sanitation. The disease range includes asymptomatic carriage, invasive intestinal disease, and extraintestinal manifestations such as liver abscess.

Intestinal amoebiasis commonly presents with abdominal pain, diarrhea that may contain mucus or blood, and sometimes fever and weight loss. Invasive disease can cause tissue destruction, colitis, and amebic dysentery. A common extraintestinal complication is amebic liver abscess, which presents with fever, right upper quadrant pain, hepatomegaly, and sometimes pleural effusion. Some infections remain asymptomatic or cause only mild symptoms.

Diagnosis relies on a combination of tests. Microscopy of stool cannot reliably distinguish pathogenic Entamoeba histolytica from nonpathogenic relatives. Stool antigen tests or PCR can detect E. histolytica. Serology supports the diagnosis of invasive disease, and imaging such as ultrasound or CT helps identify liver abscess. Endoscopy may reveal flask-shaped ulcers in intestinal disease.

Treatment for invasive intestinal disease and liver abscess typically includes a tissue-active agent such as metronidazole or tinidazole, followed by a luminal cyst--eradicating agent like paromomycin or iodoquinol to eliminate remaining organisms. Asymptomatic carriers or patients with only luminal disease are treated with a luminal agent alone. Supportive care is important in cases of dehydration or complications.

Prevention focuses on safe drinking water, proper sanitation, and good hygiene. Outbreaks are more likely in crowded settings with poor sanitation. There is no licensed vaccine.