Foot-and-Mouth Disease

Foot-and-mouth disease

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 1898 that a virus causes hoof-and-mouth disease. It was the first time a virus was reported to be the cause of an animal disease.

An infected animal can take up to four days to begin showing symptoms of fever, smacking of lips and drooling. Eventually, blisters appear on the mouth, tongue and inside of the lips and the animal becomes lame just before blisters appear in the hoof area.

Löffler, working with Dr. Paul Frosch (1860–1928), a veterinary bacteriologist, extracted lymph from the blisters on the mouths and udders of diseased cattle. The lymph was diluted in sterile water and passed through filters. The researchers expected the filtrate to be an antitoxin of foot-and-mouth disease similar to the one for smallpox .

But Löffler and Frosch were wrong; when the filtrates were injected into healthy animals, they became sick. Therefore, they concluded the causative agent was not a bacterial toxin, but instead was a non-toxin producing bacterium too small to be seen under the microscope , yet small enough to pass through the filters. It wasn't until 1957 that scientists were able to get their first look at the causative agent, one of the smallest viruses to cause an animal disease.

In February, 2001, a devastating outbreak of foot-and-mouth disease began among the stock of England's pig, sheep, and cattle ranchers. Epidemiologists (investigators in infectious disease) determined that the outbreak began in a swill (garbage) feeding farm in one county, and spread first by the wind to a nearby sheep farm, then by sheep markets to farms across the English countryside. Even before the outbreak was detected, the virus had infected livestock in 43 farms. Despite massive quarantining and culling of herds (over 4 million animals were destroyed), by the time the outbreak was contained almost a year later, the disease had spread to areas of Ireland, France, and the Netherlands.

English citizens lost billions of dollars worth of income as markets for English meat and dairy products evaporated, animals were decimated, and tourists avoided the English countryside. Use of an available vaccine to attempt to curb the epidemic was rejected by most scientists, as the virus incubation time was short (often less than 72 hours), and the immunity gained from the vaccine was short-lived. Meanwhile, the Unites States and other countries adopted inclusive measures to prevent the importation of the foot-and-mouth virus, from carefully restricting the importation of animal products, to the sanitizing of shoes of airplane passengers arriving in the U.S. from England. As of April 2002, the outbreak continued to be contained, with the last confirmed foot-and-mouth case in England occurring six months prior at a farm in Northumberland, and the restoration of "Foot-and-mouth-Free" status restored to livestock herds of the United Kingdom by the World Organization for Animal Health (Office Internationale des Epizooties).

See also Animal models of infection; Epidemics, viral; Epidemiology, tracking diseases with technology; Epidemiology; Veterinary microbiology