Biosafety experts scoured a rural laboratory Sunday in a hunt for the possible source of an outbreak of foot-and-mouth disease on a southern English farm.
Prime Minister Gordon Brown said the focus was on determining how the virus could have escaped from the facility, where the disease is researched and a vaccine manufactured. He said he was hopeful that a potentially disastrous livestock epidemic could be averted.
The agriculture department said the strain of foot-and-mouth disease found on the farm was identical to one used at the laboratory four miles away, which is shared by the government's Institute for Animal Health and a private pharmaceutical company, Merial Animal Health.
Saying the particular strain of the disease had not recently been seen in live animals, it ordered a 6-mile protection zone set up around the lab and the affected farm. The department also began an urgent review of biosecurity measures at the lab.
Experts from the Health and Safety Executive were inspecting both the Merial and the government facilities.
"The first thing, having identified a possible source of the disease, we must now look at the transmission mechanism," Brown said.
While the government has not ruled out other sources for the virus, "we are looking intensively at what's happened on this site," Brown added, saying officials are tightening biosecurity measures in the immediate area. "We hope by doing that, we will be able to control and contain (it)."
Cattle on a farm outside Wanborough, 30 miles southwest of London, tested positive for the disease, which affects cloven-hoofed animals including cows, sheep, pigs and goats. It does not affect humans. All livestock at the farm were slaughtered Saturday, as well as animals at a second farm nearby.
The agriculture department said there had been no movements of livestock from the affected farm since July 10, raising hopes the virus might not have spread further. Environment Secretary Hilary Benn said reports of symptoms at four more farms had been investigated and found not to be foot-and-mouth.
The highly infectious disease, which devastated Britain's rural economy in 2001, can be transmitted though contact between animals, or on the wind.
The Department for Environment, Food and Rural Affairs, or DEFRA, said the strain was present at the government lab and was used in a vaccine batch manufactured last month by Merial Animal Health _ the British arm of Duluth, Ga.-based Merial Ltd.
Merial suspended manufacture of the vaccine as a precaution but insisted Sunday its plants "operated to the highest level of product quality and safety."
Martin Shirley, director of the Institute for Animal Health, said the strain had been in "limited use" within the institute's own laboratory in the past four weeks but an investigation had found no breaches of biosecurity procedures.
"There are other possible sources of the virus, but they are looking pretty remote," microbiologist Hugh Pennington told the BBC, saying it was possible the virus had spread from the laboratory on the wind.
"It may not be a huge security breach," Pennington said. "It may just be one incident which let a puff of virus out."
Britain banned exports of livestock, meat and milk and halted the movement of cattle, sheep, goats and pigs nationwide to prevent the spread of the virus.
The United States and Japan immediately banned British pigs and pork products. British beef is already banned in both countries because of mad cow disease. The 27-nation European Union is likely to ban British livestock imports on Monday.
The case is the first in Britain since 2001, when carcasses of the 7 million culled cattle were burned on huge pyres that dotted the countryside. The farming industry was devastated and rural tourism was badly hit.