Study: foot-and-mouth controls possibly overdone

Cattle infected with foot-and-mouth disease are only contagious for a brief period of time - about half as long as previously thought - according to a study that will appear in the journal Science.

The research has implications for all infectious diseases, said one of the report's authors, Mark Woolhouse of the University of Edinburgh, and raises the possibility that the controversial control measures used to halt the disease's spread during a British epidemic in 2001 may not have been entirely necessary.

"This study shows that what we thought we knew about foot-and-mouth disease is not entirely true," said Woolhouse. "So, what we think we know about human influenza and other infectious pathogens might not be completely accurate either."

The report appears in the May 6 issue of the journal Science.

Researchers at Britain's Pirbright Institute for Animal Health tried 28 times to infect healthy cows with foot-and-mouth disease by placing them next to infected cattle.

But the disease was only transmitted eight times, researchers say, leading them to determine that the cattle are not actually contagious until about half a day after the first clinical symptons have appeared.

"We now know that there is a window where, if affected cattle are detected and removed from the herd promptly, there may be no need for pre-emptive culling in the immediate area of an infected farm," said Woolhouse in a statement released by the American Association for the Advancement of Science, which publishes the journal.

Once the cow is visibly infected, then it is contagious for just 1.7 days, about half the time previously thought, Woolhouse said. After that, the immune responses kick in and limit virus replication.

Woolhouse said the findings should permit new tests to be developed which can detect the disease earlier and help reduce its spread.

Rarely contractible by humans, foot-and-mouth disease is considered highly infectious among cloven-hoofed farm animals like cattle, sheep and goats. Animals with the disease develop fevers and blisters inside the mouth and on the feet.

The infection can cause enormous financial losses. During the 2001 epidemic in Britain, hundreds of thousands of cattle and sheep were slaughtered, resulting in a loss of billions of British pounds (dollars).

Woolhouse said similar studies could explain much more about other human and animal pathogens.

"We urgently need to evaluate other infections," he said in the statement. "Until we do that, we can't evaluate how effective control measures like quarantining individuals, prophylaxis, anti-virals or the pre-emptive culling of livestock are going to be."