London

Epidemiologists working on the British foot-and-mouth epidemic are blaming the relaxation of security measures for a burst of small outbreaks of the disease.

The epidemic had seemed to be under control in May (see M. Woolhouse et al. Nature 411, 258–259; 2001). The number of new cases reported each day was below five for most of June, July and August, down from a peak of more than 50 in April, and government officials hoped that the disease would be extinct by the end of the year.

But in Northumberland, more than 20 cases have been recorded since late August. Before that, no new cases had been reported there since May. “The tail of the disease is longer than had been hoped,” says Mark Woolhouse, an epidemiologist at the University of Edinburgh.

Woolhouse points to the relaxation of restrictions on moving animals and measures to stop people carrying the virus between farms. The government had allowed some movement of animals on animal-welfare grounds. Also, farmers and vets may have stopped applying restrictions so rigorously, scientists say.

Researchers say there is a chance the disease surfacing in Northumberland was carried in sheep flocks, as sheep can carry the virus without showing any symptoms.

The government has now halted animal movements in affected areas and has imposed stricter security measures. But this is causing problems for farmers in upland areas, such as Northumberland. Animals that graze on high ground in summer are normally relocated at this time of year.

Epidemiologists say it is difficult to estimate how long the epidemic will last. The onset of winter may cause problems, they add, as the virus can survive for longer in lower temperatures.