Amebiasis in acquired immunodeficiency syndrome.

Amebiasis is an infection caused by the intestinal protozoan Entamoeba histolytica (E. histolytica). About 90% of infections are asymptomatic, and the remaining 10%of infections produce a spectrum of clinical syndromes ranging from dysentery to abscesses of the liver or other organs. Most asymptomatic carriers harbor nonpathogenic strains {E. dispar) which do not cause invasive disease. Some patients infected with pathogenic strains do not develop invasive amebiasis and remain asymptomatic. Host factors play a role in the development of invasive disease. Epidemiologically amebiasis is one of the most important infectious diseases in the world. About 10%of the world's population (more than 500 million people) is infected with E. histolytica. Areas of highest incidence are developing countries including Central and South America, tropical Asia and Africa. Amebiasis is the third most commoncause of death from parasitic disease after shistosomiasis and malaria. In developed countries, travelers, immigrants and homosexual men are at risk. Patients with acquired immunodeficiency syndrome (AIDS), an advanced human immunodeficiency virus (HIV) infection, are in the highest risk group of invasive amebiasis. Patients with HIVinfection develop various kinds of opportunistic infections. Diarrhea secondary to opportunistic pathogens is a commonproblem in HIV-infected patients. Morbidity and mortality are increased in AIDS patients with chronic diarrhea secondary to opportunistic infections, and chronic diarrhea is an independent marker of a poor prognosis (1). The most commoncause of lower gastrointestinal bleeding in AIDS patients is thought to be cytomegalovirus (CMV)colonic disease (1), and in one study amebic colitis and CMVcolitis were the two leading causes of prolonged diarrhea in patients with AIDS (2). Most HIV-infected individuals with asymptomatic amebic infection have E. dispar but some of them can develop invasive amebiasis by E. histolytica (3). Amebiasis is an important emerging opportunistic infection in AIDSpatients in an area endemicfor amebic infection, where food-borne exposure is prevalent. For example in Taiwan (4), 6.1% of the patients with HIVinfection have invasive amebiasis. In India it is reported that Cryptosporidium sp. (94.4%) and Isospora sp. (10.7%) are predominant over E. histolytica (5.6%) among the HIV positive asymptomatic injecting drug users (5). On the other hand, in developed countries the incidence of amebiasis is low among HIV-infected patients: 13.5 cases per 10,000 person-years in the United States (6). However it is important as one type of sexually-transmitted diseases: transmitted by oral and anal sexual practices. While the overall prevalence of amebiasis is approximately 4%in the United States, certain high-risk groups have a muchhigher incidence of infection and disease. Prevalence of E. histolytica or E. dispar in the gay population of NewYork City and San Francisco approached 40 to 50% (7). Some Japanese literature (8, 9) also showed homosexual contact was an important risk factor for amebic infection.