Entamoeba histolytica: Clinical Update and Vaccine Prospects.

Amebiasis is extraordinarily common in children of the developing world. This realization has come from application of diagnostic techniques that distinguish the nonpathogenic parasite Entamoeba dispar from Entamoeba histolytica. E. histolytica infection is found in children with dysentery, diarrhea, and in many cases in children with no gastrointestinal symptoms. Genetically distinct strains of E. histolytica exist but evidence is too preliminary to judge if some strains are more virulent than others. A provocative study from Tanzania has shown that pregnant women with HIV infection who are coinfected with E. histolytica are at greater risk of delivering a low birth weight infant. Perhaps the most exciting new data is the identification of acquired immunity to recurrent E. histolytica infection. Acquired immunity is linked to a mucosal immune response against a major virulence factor of the parasite, a Gal/GalNAc lectin responsible for adherence and killing of the host. Prospects for a vaccine are thus brightening at the same time that the true burden of disease is comprehended.