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  • Genetic codes of cattle-killing parasites cracked


[NAIROBI] African, British and US scientists have together mapped the genetic codes of two parasites that kill millions of cattle in developing countries each year.

Theileria parva and Theileria annulata cause East Coast fever and tropical theileriosis, respectively. They are transmitted by ticks and cause severe fever, often followed by death. 

"[These diseases] affect the livelihoods of the poorest farmers in developing countries, making it difficult for them to feed their families," says Andy Tait of the University of Glasgow's veterinary school, in Scotland, who helped decode the genome of T. annulata.

Both genetic codes were published in last week's issue of Science.

The researchers hope that studying the codes will help efforts to develop safe, effective and inexpensive vaccines against the parasites.

Efforts to tackle the two diseases currently focus on killing ticks with pesticides, but these are costly, and signs that ticks are growing resistant to them have been reported in many countries.

The genome of T. parva was cracked by researchers at the International Livestock Research Institute (ILRI) in Nairobi, Kenya, and The Institute for Genomic Research (TIGR) in the United States.

The parasite invades the animals' white blood cells and turns them into cancer-like cells that multiply rapidly and eventually lead to fever and death. It kills one million cattle every year in sub-Saharan Africa, costing nearly US$170 million.

Carlos Sere, ILRI's director-general, says the research is a significant step towards developing an effective vaccine to control East Coast fever.

This would be of great economic value to developing countries, especially in areas where pastoral communities — such as the Maasai, Samburu and Pokot people in Kenya — use cattle as a form of currency.

By studying the parasite's genetic code, scientists also hope to learn about how human cancers form.

"This parasite has an astonishing ability to induce cancer in its host cell in a way that is reversible," says Vish Nene, a TIGR researcher. "There are clear links to cancer biology in humans and this study has given us clues to pursue."

The genetic code of T. annulata was mapped by researchers at the Wellcome Trust Sanger Institute and the Veterinary School of Glasgow University, both in the United Kingdom.

This parasite causes tropical theileriosis, a disease similar to East Coast fever that threatens more than 250 million cattle in China, India, the Middle East, north Africa, southern Europe, and the southern Russian republics. It kills up to 70 per cent of the animals it infects.

The researchers at the Sanger Institute identified several genes that might allow the parasite to trigger and maintain a tumour-like state in infected host cells, says Arnab Pain, who led the research. He says his team will now try to understand how to block these genes.

Malcolm Gardner, who led the research on T. parva, says this work will also be helpful to scientists who study malaria, as the two parasites are similar.

Link to full paper on T. parva in Science

Link to accompanying commentary in Science

Reference: Science 309, 134 (2005) 

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