researcH: tissue destroyer sequenced

24 February 2005

Researchers at the Wellcome Trust Sanger Institute and colleagues in the USA have completed the genome sequence of the parasite that causes amoebic dysentery, Entamoeba histolytica ('tissue destroyer').

Amoebic dysentery is, after malaria, the second-biggest protozoan parasite killer. Each year, an estimated 50 million cases cause up to 100 000 deaths, mostly in developing countries.

The disease is caught by ingesting cysts – dormant organisms – from water, food or hands contaminated with human faeces. Inside the gut, the parasite hatches and begins multiplying, causing diarrhoea, fluid and salt loss and bleeding.

The genome sequence reveals almost 10 000 genes, some of which appear to have been acquired from the bacteria that E. histolytica feeds on. The parasite uses a range of genetic tricks to evade our defence mechanisms: large 'families' of genes produce its surface coat, and it may use different coats to avoid detection in the human body for years at a time.

The parasite seems to have discarded many genes required for independent survival, relying instead on its human host. Conversely, genes it appears to have picked up from bacteria allow it to use a wider range of sugars and other energy sources.

These findings give a fascinating glimpse of how this ancient parasite evolved and adapted to its environment. They also highlight unusual metabolic processes, including many enzymes and transporters encoded in its genome, that may be exploitable as drug targets.

The sequencing was carried out by the Wellcome Trust Sanger Institute and The Institute for Genomic Research (TIGR), USA, and was supported by the Wellcome Trust and the National Institute of Allergy and Infectious Diseases, part of the US National Institutes of Health.

External links

• The genome of the protist parasite Entamoeba histolytica (Research paper, Loftus B et al.)
• The Pathogen Sequencing Unit (Wellcome Trust Sanger Institute website)