London

Beleaguered British farmers are reeling from another animal health crisis this week, after cases of foot-and-mouth disease were confirmed at locations across the country. It is the first major outbreak of the highly infectious disease to affect Britain in over 30 years.

The government acted quickly to halt movement of animals after vets from the government-funded Institute for Animal Health (IAH) found cases at an abattoir in Essex.

Eleven further outbreaks had been confirmed by 27 February, including one at a sheep-exporting business in southwest England. The possibility that the disease may have been exported led France, Germany, Belgium and the Netherlands to introduce measures restricting movement of animals that had recently arrived from Britain.

Intensive farming practices and the increased movement of livestock, which has resulted from the closure of local abattoirs in response to the outbreak of bovine spongiform encephalopathy, have been blamed in the press for the scale of the outbreak. But experts say that these factors are of little importance.

Peter Roeder, an animal health officer at the United Nations' Food and Agriculture Organization, points out that foot-and-mouth disease is already endemic in some areas of southern Africa and parts of Asia. Imports of foodstuffs from these regions are strictly controlled, but customs officials say it is impossible to block illegal imports completely.

The UK virus is one of seven known types of the disease. Called type O, it originated in India before spreading east into China, Japan, Korea and Taiwan. It arrived in South Africa last year, but has been eradicated there by slaughtering potentially infected cattle.

Dead meat: pyres burn in Britain as farmers struggle to contain foot-and-mouth disease. Credit: PA

Slaughtering of livestock has already begun in Britain, as existing vaccines can stop symptoms but do not prevent animals from carrying or spreading the disease. "The virus can exist in vaccinated cattle for up to three years," says the IAH's Paul Kitching, "and trade restrictions reflect this. To resume trade a country has to be totally free of the disease."

Making the vaccine, which requires large amounts of the live virus, is also risky. Outbreaks from vaccine production centres have persuaded several European countries to end vaccination programmes.

Vaccine development is further complicated by the virus's high mutation rate. This leads to the existence of numerous subtypes within each type, some of which may require different vaccines. The IAH is responsible for matching vaccines to the hundreds of samples it receives from around the world every year. It dealt with 400 samples last year but, says Kitching, the true number of outbreaks is "uncountable".

The IAH, Pfizer and Eli Lilly each have groups working on new vaccines. "Safer, more stable vaccines are possible," says Kitching, "but it is highly unlikely that a new vaccine will eliminate all the problems."