British authorities say tests for foot-and-mouth disease in livestock on a fourth farm in England have proved negative.
Chief veterinary officer Debby Reynolds said Saturday the latest tests on a farm near Dorking in southeastern England showed no presence of the highly infectious virus.
The farm is located about 20 kilometers outside the main surveillance zone in Surrey, where livestock on two farms have tested positive for the foot-and-mouth virus. Tests on a third farm within the surveillance zone were negative.
Reynolds warned farmers to continue exercising relentless vigilance, despite signs that the infection is being contained.
Almost 600 animals have been destroyed so far to prevent the spread of the livestock disease.
Foot-and-mouth disease is not harmful to people. However, farmers are afraid of a repeat of the outbreak in 2001, when almost seven million animals were slaughtered, devastating Britain's agriculture industry.
Health investigators believe there is a strong possibility the latest outbreak started in a research laboratory close to the farms. One of the labs, the privately run Merial Animal Health laboratory, rejects the claim, and says there is no evidence the virus was transported out of its center by humans.
The disease affects cloven-hoofed animals such as cows and pigs and is spread mostly through direct contact between animals or through contaminated feed.
Some information for this report provided by AP, AFP and Reuters.