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Cattle

A sure shot

Vaccine ensures that only animals infected with the foot-and-mouth disease be slaughtered

A researcher from Minas Gerais has developed an alternative vaccine – of the recombinant kind, made by genetic engineering – against the cattle raisers’ terror: foot-and-mouth disease, a viral disease that makes cattle lose weight, their ability to move, and their reproductive potential. In a herd where the infection is found, they all have to be slaughtered, a legal requirement to prevent the advance of one of the most contagious diseases that exists: it can infect a thousand animals a day. The advantage of the vaccine by Mauro Moraes, from the Federal University of Viçosa (MG), is that it makes it possible to identify the infected animals and to save the rest.

Moraes, who developed the vaccine in the two years he spent in New York, as a lecturer at the American government’s Plum Island Animal Disease Center, did not use the complete dead virus, as it is common. Instead of that, it is an inoffensive type 5 human adenovirus that acts as a vector, carrying only the proteic structure of the virus – called capsid. This part contains two strips of the codifying sequence of the so-called structural proteins: P1, taken from the A24 strain , and 3C, from the A12 strain. These are the strips that work as antigens. They activate the production of antibodies against thefoot-and-mouth disease. This procedure also does away with the molecule of RNA (ribonucleic acid), which contains the genome of the virus and ensures its reproduction.

Tested on 38 Yorkshire pigs, the vaccine was 100% efficient – the same as the commercial product, which was taken as the comparison standard. There was one experiment with 24 animals, and another with 14. They received just one dose of the vaccine, and were then challenged by the live virus, in three stages: 7, 14 and 42 days afterwards. In the end, only the animals in the control group – those not vaccinated – developed the signs of the disease. The results laid the foundations for an article by Moraes, accepted for publication in the Vaccine magazine.

The new vaccine offers fewer risks. In the use of the current vaccine, it is difficult to distinguish between animals that are infected and those that are not. Both the protection generated by the vaccine and the response to the attack by the real virus are measured by the presence of antibodies in the animals’ blood. The problem is that, with this examination, there is no way of distinguishing the antibodies produced in response to the virus from those that are the result of the application of the vaccine. As it made only from the proteins of virus cover, it leads to very limited reactions, thus making it possible to tell he presence of antibodies caused by it from those resulting from the infection.

It would therefore be possible to recognize and to eliminate the infected animals. “The recombinant vaccine could be used in cases of emergency, lowering the costs of combating the disease”, says the researcher. Another advantage is its decentralized production. Moraes believes that the vaccine can be made without risk in foot and mouth free regions, which current legislation does not allow, for fear of the virus spreading in the air. “Even laboratories with little experience in handling viruses could multiply the adenovirus with the antigen, without any danger”, he points out. Today, making the virus inactive and producing the vaccine are concentrated on high security laboratories.

Moraes did a test with four head of cattle. “The vaccine also gave protection, but a lot of work is still needed until the best dosage is defined”. To move on, he needs a security level 3 laboratory at Pedro Leopoldo, near to Belo Horizonte (MG), which the Ministry of Agriculture is building this year. The laboratory will carry out the control of medicines and research: it will be the only public installation suitable for dealing with the foot-and-mouth virus. “Production depends on private initiative, but companies with experience in vaccines would have no major difficulties, since it is a question of producing a virus with technology used in other systems”.

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