an international team of researchers, including several from Delhi's Jawaharlal Nehru University (jnu) and the Bose Institute in Kolkata, have sequenced the genome of the gut parasite Entamoeba histolytica. The unicellular organism causes a diarrhoeal disease that kills almost 100,000 of the 48 million people it annually infects, mainly in tropical countries.
E histolytica is the first-ever amoeba whose genome has been mapped. The analysis has thrown light on how the microorganism has come to acquire an amazingly complex repertoire of sensory genes and a variety of bacterial-type genes. The findings were reported in the February 24 issue of Nature (Vol 433, No 7028).
The mapping revealed E histolytica genome degrades when it switches from a free-living organism to a parasite in the human gut. Simultaneously, the amitochondrial (lacking mitochondria, which help cells produce energy) germ picks up several metabolic genes from bacterial co-inhabitants of the human gut and might be then re-engineering them, according to Brendan Loftus of the Institute of Genomic Research, who led the research effort.
This fascinating aspect of the parasite may be exploited as drug targets, the scientists concur.
The project also identified large families of surface proteins that might be enabling the amoeba to evade the human immune system and stay hidden in the body for years at a time. Such information may help researchers find better means to harness the immune system to eradicate infection through vaccine development.
Says Alok Bhattacharya of the School of Life Sciences at jnu, a collaborator of the study, "The genome sequence will help identify new drug and vaccine targets," and also may help researchers understand why the disease occurs in only a small fraction of those infected. "Intestinal infections are one of the major health problems in developing countries," he adds. Typically, the parasite is transmitted through contaminated food or water.
The disease can cause liver damage but more often causes dysentery -- a severe form of diarrhoea often associated with blood in the faeces. Unchecked, the diarrhoea can be fatal, especially in children. According to a field study in Bangladesh, E histolytica infection occurred at least once in as many as 80 per cent of 300 children examined. Over a period of four years, about a third of the infected children suffered from amoebic colitis, an ulceration of the stomach lining.
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