Livestock vaccine to aid Africa

June 26, 1998

MORE than a million African livestock could be saved from death every year as field trials start on a new vaccine that could revolutionise the lives of poor farmers.

An international team of researchers in Edinburgh, France, Africa and the United States has developed a vaccine against hear****er, a tick-borne disease that affects millions of cattle, goats and sheep in semi-arid regions of southern Africa.

The disease is carried and passed on by colourful ticks, Amblyomma hebraeum, which feed off the animals' blood. Each female tick lays between 2,000 and 3,000 eggs, which hatch into larvae, gorging themselves on the host animals' blood before dropping off and turning into nymphs.

If the nymph then feeds on an animal infected with the organism Cowdria ruminantium, it will become infected and, when it has become an adult, will pass on the organism to other animals. Cowdria ruminantium attacks the nervous system, leading to death.

The majority of African livestock go unprotected against the killer disease, which was isolated more than 75 years ago.

The classic methods of protecting animals, by infecting them with live organisms and then treating them with antibiotics until they recover, have proved too difficult and expensive.

Keeping fresh live organisms has required a constant supply of infected animals from which blood can be taken to infect other animals. This blood then has to be delivered intravenously.

But now scientists have developed a method of growing Cowdria ruminantium in animal cells in culture outside the animal host, producing large numbers of infective organisms. These organisms, if inactivated or killed, can provide an antigen on which the new vaccine is based.

Livestock can then be vaccinated with the dead organisms, which can be kept indefinitely at room temperature and delivered simply, providing immunity without infection. Initial tests have shown the vaccine will protect 70 per cent of animals.

Duncan Brown, of the Centre for Tropical Veterinary Medicine at the University of Edinburgh and manager of the government's Department for International Development's animal health programme, said: "Hear****er affects the animals of the poorest people in Africa. In response to El Ni$o or drought, pastoralists move their animals to new areas which exposes them to infected ticks carrying new forms of the disease.

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