Foot and mouth disease (FMD) is so highly contagious–and such a threat to farm economies–that the United States won’t allow researchers to work with the virus on the mainland. But in Britain, a lab making Foot and Mouth vaccines was located near herds of cattle and might have been the cause of a new outbreak.

FMD does not typically infect humans, but its appearance among farm animals can have a swift and far-reaching economic impact–several countries, including the United States, have banned imports of British livestock, and Britain has suspended exports of livestock, meat, and milk products and destroyed more than 100 cows since the outbreak was discovered last week.

(Horses cannot be infected by FMD, but can carry the virus on their hooves, skin, hair, and possibly in their nasal passages.)

Britain’s health and safety agency says there was a “strong probability” the outbreak originated at the Pirbright laboratory southwest of London and was spread by human movement. The laboratory houses both a government Institute for Animal Health research center and vaccine-maker Merial Animal Health.

Lab accidents have resulted in human cases of everything from meningitis to Ebola, but are rare and most are self-contained. Still, diseases that can kill humans have made it out of labs.

“With the amount of virus there is in laboratories around the world, I’m surprised that this kind of thing doesn’t happen more often,” said Juan Lubroth, DVM, PhD, Dipl. ACVPM, head of infectious diseases at the Food and Agriculture Organization.

FMD is the most contagious disease among mammals. In the United States, which has been free of the disease since 1929, it is illegal for anyone to possess the virus outside of a single research laboratory on Plum Island, New York. Germany employs the same policy. Some experts think that by restricting the virus’ use to an is