Amebiasis/Amebic Liver Abscess Fact Sheet

Amebiasis is a parasitic disease of worldwide public health importance. Approximately 100,000 people throughout the world die annually from amebiasis infection, making this infection the second leading cause of death from parasitic diseases. It is caused by a one-celled parasite, Entamoeba histolytica. Amebiasis occurs mainly in developing countries having poor sanitary conditions and is more severe among the young and old and in patients receiving corticosteroids. In the United States, it is found in immigrants, travelers to developing countries, people living in institutions with poor sanitary conditions and male homosexuals.

Cause of amebiasis

Amebiasis is a protozoan infection of the lower GI tract. The causal parasite, E. histolytica, exists in two forms: the trophozoite and the cyst. Infection ensues with the ingestion of viable cysts in fecally contaminated food and water. The cyst passes through the stomach and small intestine and excystation occurs in the bowel lumen. Sexual transmission of E. histolytica results in enteric infection with possible dissemination of venereal infection in males and females.

Symptoms of amebiasis

Most people (90%) infected with E. histolytica remain asymptomatic, while a varied array of clinical syndromes ranging from diarrhea, dysentery and colitis to abscesses of the liver, spleen and brain develop in the remaining 10%.

The most common symptoms of infection include:

Intermittent diarrhea and constipation
Flatulence
Cramping
Abdominal pain
Stools may contain mucus and blood

The incubation period for infection is 7-28 days.

Incidence and prevalence of E. histolytica infection

The prevalence of infection with E. histolytica worldwide is estimated to be 50 million cases each year, with about 10 times as many cases of E. dispar, a non-pathogenic organism recently discovered to be genetically distinct from the pathogenic E. histolytica. Prevalence is highest in Central and South America, Africa and Asia.

In the United States and other developed countries, the infection is rare, but when found tends to be more common among persons with a history of travel or residence in developing countries. In 1993, approximately 3,000 cases were recorded in the US, with most of the cases arising in immigrants from Mexico, Central and South America (33%), and from Asia or the Pacific Islands (17%).

Diagnosis of amebiasis

The diagnosis of amebiasis is based on detection of cysts or trophozoites in the feces. Methods for diagnosis include microscopy; stool culture; antigen detection; serology; and molecular probes, such as polymerase chain reaction. The use of diagnostic tools with high diagnostic efficacy is important to separate E. histolytica (pathogenic) from Entamoeba dispar (nonpathogenic).

Prior to more sensitive tests becoming available, E. histolytica diagnosis had been based primarily on examinations of stool for ova and parasites which resulted in not differentiating the commonly occurring, nonpathogenic species, E. dispar.

Treatment of amebiasis

Tindamax^® (tinidazole) is a well-tolerated, highly effective treatment for amebiasis. Tinidazole's average cure rates are 92% for intestinal amebiasis and 93% for amebic liver abscess.^1,8-16