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March 1997 |
WHO/PAHO/UNESCO REPORT
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March 1997 |
Recommendations List of Participants
Introduction
Amoebiasis is currently defined as infection with the protozoan parasite Entamoeba histolytica. Normally resident in the large bowel, amoebae occasionally penetrate the intestinal mucosa disseminate to other organs. The factors that trigger invasion are unknown. E. Histolytica is responsible for up to 100,000 deaths per annum, placing it second only to malaria in mortality due to protozoan parasites. It has long been known that many people apparently infected with E. Histolytica never develop symptoms and spontaneously clear the infection. This was interpreted by many workers as indicating a parasite of variable virulence. However, in 1925 Emile Brumpt suggested an alternative explanation, that there were in fact two species, one capable of causing invasive disease and one that never causes disease, which he called E. dispar. Brumpts hypothesis was dismissed by other workers.
In 1970s, data started to accumulate that gave support to Brumpts hypothesis of the existence of two distinct organisms within what was being called E. histolytica. Biochemical, immunological, and genetic data continued to accumulate and in 1993 a formal redescription of E. histolytica was published, separating it form E. dispar.
E. histolytica can cause invasive intestinal and extraintestinal disease, while E. dispar can not. The confirmation of these two distinct species of Entamoeba is perhaps the major recent accomplishment in the field of amoebiasis research. In addition, proteins associated with virulence have been identified, including a lectin that mediates adherence to epithelial cells, a pore-forming peptide that lyses host cells, and secreted proteases that degrade host tissues. All of these virulence proteins, as well as other unique antigens present on the parasite surface are potential targets for anti-amoebic vaccines. Biochemical studies have identified the bacteria-like fermentation enzymes, which are the target of metronidazole, the most potent anti-amoebic drug in tissues, and suggest new targets for anti-amoebic drugs. This consultation was called to evaluate the implications of this recent work.
Conclusions
Recommendations
List of participants
Source:Divison of Disease Prevention and Control, Communicable Diseases Program, (HCP/HCT), Division of Tropical Diseases, Schistosomiasis and Intestinal Parasitosis Unit, WHO.
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