Genomics accelerates East Coast Fever vaccine hunt

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[NAIROBI] Researchers say the science of genomics is revolutionising the hunt for a vaccine against a parasitic disease that kills one million cattle in Africa each year, costing poor farmers US$200 million.

In a paper published online this week by Proceedings of the National Academy of Sciences, the scientists report that eight of the Theileria parva parasite’s proteins are promising vaccine candidates.

“Earlier attempts to identify vaccine candidates resulted in only two molecules in a decade,” says Evans Taracha of the Kenya-based International Livestock Research Institute.

By using genomics — the study of an organism’s entire genetic code and the proteins it produces — the team have found eight proteins in two years.

“It demonstrates the power of using a rational approach incorporating new science to solve a complex issue,” says Taracha.

The genome of T. parva, which causes East Coast Fever, was mapped last year (see Genetic codes of cattle-killing parasites cracked).

Taracha and colleagues already knew that some of the parasite proteins can trigger an immune response in cows, and that the immune system of previously infected cattle can ‘recognise’ new infections and fight them.

When the parasite infects the cow’s white blood cells, fragments of parasite proteins attach to proteins on the surface of the blood cell.

The presence of ‘foreign’ proteins alerts the immune system to fight the infection, and once the blood cells have identified it, they are able to ‘remember’ the protein so they can rapidly recognise future infections.

Taracha and colleagues at The Institute for Genomic Research in the United States, looked specifically for T. parva genes that make proteins with the right structure to be secreted into infected blood cells.

They found that 400 of the parasite’s 4,000 genes had this trait; further testing narrowed this down to 55 genes.

In laboratory tests, eight of the proteins made by these genes triggered an immune response from the white blood cells of cattle that were naturally immune following earlier infections.

The researchers are now investigating the molecules’ potential as components of a vaccine. They hope that multiple proteins could be incorporated into a single vaccine, as this would make it unlikely that the parasite would become resistant to it.

“This vaccine would be a key component of a programme for controlling East Coast Fever and would constitute a sustainable solution to the intractable negative effects of the disease most suffered by poor smallholder farmers,” says Taracha.