“They certainly protect against clinical signs so you won’t necessarily know that an animal has been infected. It can be replicating the virus and acting as a source of infection for animals that haven’t been infected and they can become persistently infected.”Here is the nub of the problem. A vaccinated animal carries antibodies against the FMD virus. It can appear quite healthy yet still carry and pump out the virus from its respiratory tract. The only tests currently available for FMD are based on identifying the presence of antibodies, so they cannot distinguish between a non-infected vaccinated animal from an infected creature.There are some attempts at rectifying this problem. For instance, Fred Brown, a British virologist working at the US Plum Island Animal Disease Center in New York, has developed a test that picks out the presence of antibodies specific to an FMD protein that is only present in the early stages of viral replication.

This means the test is able to distinguish between the actively replicating virus of a true infection, from the presence of inactivated, non-replicating virus in vaccinated animals.”We can grow the virus in tissue culture and this particular protein stays behind in the culture cells when you extract the virus. So you can make a vaccine from that virus, inject it into livestock and the animals’ immune systems won’t make antibodies against that particular protein because it wasn’t present in the vaccine,” Brown says.”But if an animal has been infected with FMD virus, that protein will have been present and you will find antibodies against it in the blood. So, to differentiate between an animal that’s been vaccinated and one that was actually infected with FMD virus, you could run tests to check for antibodies against that indicator protein,” he says.The problem is that the test is still not commercially available and further field trials, lasting another two years, are needed. Countries that are free of foot-and-mouth disease and which do not vaccinate their animals therefore have no means of discriminating between imported animals that are vaccinated but healthy from imported animals that are vaccinated and infected.

The result is that countries that are free of disease have imposed a ban on livestock from countries that claim to be free but still use vaccines as a prophylactic against infection.Here is where the economics of vaccination become inextricably mixed with the science. In theory, if every country adopted vaccination the problem should go away and the virus might be eradicated, similar to the way that a global vaccination campaign has eradicated smallpox in the human population In practice, however, this is impossible. Not only would every cloven-hooved farm animal have to be vaccinated, but so would every other susceptible animal in zoos and the wild. As this is impossible, vaccinating livestock would inevitably lead to the establishment of a reservoir of virus in wildlife. It would result in foot-and-mouth becoming endemic.In addition, the cost of vaccinating every domestic animal at least twice would be prohibitively expensive even for developed countries. More expensive, even, than having to deal with an occasional outbreak by aggressive culling, according to David Harvey, from Newcastle University’s Centre for Rural Economy.He estimates that if Britain had adopted national FMD vaccination following the 1967 epidemic, the capital costs over the past 34 years would be about £5bn.