Single doses of a genetically-engineered vaccine could eradicate both rinderpest and capripox, two viral diseases which kill millions of cattle, sheep and goats in developing countries every year.
The vaccine has particular significance because the regions where outbreaks of the two viruses occur overlap, says Donald Black, head of the capripox virus group at the Agricultural and Food Research Council鈥檚 Institute for Animal Health. He and colleagues at the institute鈥檚 Pirbright laboratories near Woking in Surrey have developed the first vaccine to provide resistance against both rinderpest and capripox. 鈥業t should cost half the price of two separate vaccinations,鈥� says Black.
Rinderpest, a German word meaning 鈥榗attle plague鈥�, makes cattle salivate profusely and triggers serious diarrhoea, which dehydrates and kills them. Animals infected with the capripox virus develop a condition called 鈥榣umpy skin disease鈥� (LSD). Unsightly lumps of hard tissue grow on their hides, rendering them unsaleable. They also develop internal lumps which kill the animals by disrupting their internal organs. Variations of the same virus also cause the fatal diseases sheep-pox and goat-pox. Between them, these diseases destroy the livelihoods of thousands of farmers in central Africa and southern Asia, every year.
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There are orthodox LSD vaccines, but 20 per cent of animals vaccinated develop an unsightly and painful sore. And while a rinderpest vaccine has been around for some years, it is unstable in hot conditions and loses its effectiveness unless stored in ice before use. 鈥楾his is a nuisance and a costly travel expense in many developing countries,鈥� says Black.
The key agent in the double vaccine is a harmless strain of the live capripox virus, originally isolated in Kenya. It resembles the active virus, and so gives resistance against LSD and the other forms of capripox virus in sheep and goats.
Into this, the researchers inserted strands of the rinderpest virus that trigger strong immune reactions in cows. The strands, stretches of bases found in the genome of the rinderpest virus, carry the genes for manufacturing the 鈥榝usion protein鈥� and the 鈥榟aemagglutinin protein鈥�. Earlier experiments have found that the presence of these proteins stimulates the bovine immune system against the rinderpest virus.
Black made copies of these genes and spliced the material into tiny loops of DNA called plasmids. They were then integrated into the DNA of the harmless form of the capripox virus by injecting them together into animals cell cultures.
鈥榃e should be able to eradicate, not just control, some of the major diseases affecting farm animals,鈥� says Black. Already, the Pirbright team has used the new vaccine to give a sample of British cattle complete immunity to lethal strains of LSD and rinderpest. In the same tests all unvaccinated animals died.
With the support of Britain鈥檚 Overseas Development Administration, Black has begun trials at the Kenya Agricultural Research Institute in Muguga near Nairobi. So far about 50 cattle and a similar number of sheep have been vaccinated. Black hopes the three-year trial will confirm that only one vaccination is necessary.
