THE first steps have been taken towards creating a cheap edible vaccine to protect sheep and goats against goats’ plague, a serious problem for farmers across Africa, the Middle East and south Asia.
M. S. Shaila’s team at the Indian Institute of Science in Bangalore has genetically modified peanut plants to produce one of the coat proteins of the peste des petits ruminants (PPR) virus. (The leaves of peanuts are often used as fodder in India.) Sheep fed leaves from the modified plants produce high levels of antibodies to the protein, hemagglutinin neuraminidase, she found. The next, crucial step will be to see if sheep fed the leaves can fight off the PPR virus, a close relative of the rinderpest and measles viruses.
A live weakened strain of the PPR virus is already used to immunise animals in Africa, and a similar vaccine is being developed for south Asia. But conventional vaccines are expensive to produce and have to be refrigerated, a major problem in remote regions. An edible vaccine would be far cheaper to produce and would last longer without refrigeration. And because it contains only one viral protein, it would allow vets to distinguish between vaccinated and infected animals.
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But there is a long way to go. One of the problems with edible vaccines is controlling the dose. Too little might leave animals unprotected. But levels of the viral protein vary depending on growing conditions, and up to 99 per cent of the protein is destroyed in the stomach. While Shaila’s team fed animals precise amounts of leaves it would be more difficult to do this on farms. The transgenic crop would also have to be grown under strict supervision to ensure it did not contaminate peanuts grown for human consumption. If it is successful, though, it will be an example of how developing countries can use GM technology to solve local problems.
To date, the only successful tests of an edible vaccine for livestock have been carrried out by ProdiGene of Texas. Pigs fed its modified maize are protected against transmissible gastroenteritis virus. But the work hit the headlines for the wrong reasons last year when ProdiGene was fined for letting the swine vaccine maize contaminate soya fields (91av, 22 March, p 15).