Entamoeba histolytica, the causative organism of invasive intestinal and extraintestinal
amebiasis, infects approximately 50 million people each year, causing an estimated 40 to 100 thousand deaths annually. Because amebae only infect humans and some higher non-human primates, an anti-amebic
vaccine could theoretically eradicate the organism. Uncontrolled epidemiologic studies indicate that acquired immunity to amebic
infection probably occurs and that such a
vaccine might be feasible. Application of molecular
biologic techniques has led to rapid progress towards understanding how Entamoeba histolytica causes disease, and to the identification of several amebic
proteins associated with virulence. These
proteins are now being evaluated as potential
vaccine components. Parenteral and oral
vaccine preparations containing recombinant amebic
proteins have been effective in preventing disease in a gerbil model of
amebic liver abscess. Although systemic and mucosal cellular and humoral immunity both appear to play a role in protection against Entamoeba histolytica, the relative importance of each in the human immune response remains unknown. No animal model of
intestinal amebiasis currently exists, moreover, so it has been impossible to evaluate protection against colonization and
colitis. Further investigation of the fundamental mechanisms by which Entamoeba histolytica causes disease and of the human immune response to amebic
infection is necessary to assess the true feasibility of an anti-amebic
vaccine.