Entamoeba histolytica |
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Amebiasis
Despite advances and improvements in health care over the past century, diarrheal diseases continue to exert a staggering disease burden worldwide. One of the most common diarrheal diseases is amebiasis, caused by the parasitic protist Entamoeba histolytica, which accounts for between 40-100,000 deaths annually. Amebiasis is predominantly seen in developing countries where a high prevalence of infection is due to fecal contamination of food and water supply, factors that cannot be immediately remedied due to limited financial resources in these countries. There is no vaccine against amebiasis and although it can be treated with nitroimidazole, side effects are common and resistance has been observed in other protozoa. E. histolytica has been listed by the NIAID as a category B priority pathogen due to its low infectious dose and potential for dissemination through compromised food and water supplies in the United States. Entamoeba histolytica Transmission of E. histolytica is primarily through the ingestion of cysts which may either result in asymptomatic colonization of the large bowl (as in approximately 90% of cases) or to symptomatic disease, usually amoebic colitis or amoebic liver abscesses. When the cyst enters the host gut excystation occurs in the intestinal lumen to produce trophozoites. The trophozites can attach to the gut lumen causing then an asymptomatic infection with clonal replication of the trophozoite followed by encystment. If however, the trophozoite penetrates the mucin layer and attaches to the host cell, the host cell will die and the parasite will follow the course of invasive disease. Disruption of the colonic epithelium results from the contact of the amoebae and due to the severe inflammatory response of the host. Damage of the colon leads to ulceration and also allows the parasite to spread in the blood to other organs, most commonly the liver. The Entamoeba histolytica genome The Entamoeba genome is ~24 Mb in size with an undetermined karyotype. A draft genome sequence of Entamoeba histolytica has been completed by TIGR and the Sanger Institute (UK). The genome is predicted to have roughly 10,000 genes. Efforts have been initiated at both genome centers to close the genome and a physical Map is being generated by the Dear Lab, at the National institute for Medical Research (UK). Comparative Entamoeba sequencing The model species Entamoeba dispar and Entamoeba invadens are scheduled to be sequenced to 8x coverage by TIGR. Low coverage sequencing of these species and of E. terrapinae and E. moshkovskii has been carried out by the Sanger Institute. Other Web Resources: The Entamoeba home page TIGR Entamoeba projects The Sanger Institute Entamoeba projects |
