Often inaccurately called hoof-and-mouth disease, this highly contagious virus causes blisters in the mouth and on the feet surrounding hoofs of animals with cleft, or divided hoofs, such as sheep, cattle and hogs. The disease was first noted in Europe in 1809; the first outbreak in the United States came in 1870. Although it seldom spreads to humans, it can be transmitted through contaminated milk or the handling of infected animals.

Outbreaks are expensive for the animal owners who must kill the infected animals and incinerate or bury or them in quicklime. Then the animals' living quarters are disinfected, while feed and litter are burned. The farm is quarantined by state and federal officials who can decide to extend the quarantine to the general area or the whole state. Friedrich August Löffler (1852-1915), a German bacteriologist who discovered the bacillus of diphtheria in 1884, also demonstrated in...