Foot-and-Mouth Disease

Foot-and-Mouth Disease, also known as hoof-and-mouth disease, a highly infectious viral disease of animals with cloven hooves, such as cattle, swine, sheep, goats, and deer. The disease does not affect humans. One of the most contagious animal diseases, the virus that causes foot-and-mouth disease spreads rapidly, resulting in widespread epizootics (epidemics among animals). Since the disease commonly affects animals raised for food or other products, an epizootic can create extensive losses to the agricultural sector of a country’s economy.

Symptoms vary among affected animals. Cattle and pigs with foot-and-mouth disease develop a sudden fever, followed by an eruption of blisters around the hooves, in the mouth and nose, and on the udders of females. Most sick animals salivate excessively, and some animals are unable to stand because their hooves become tender and painful. Sheep and goats may be infected with the disease without showing any symptoms.

The disease is often fatal for young animals. Mature animals infected with foot-and-mouth disease usually recover, but they become severely debilitated. Livestock raised for meat lose weight, milk production in dairy cattle decreases, and pregnant animals often abort. Animals may carry the virus for up to two years.

The foot-and-mouth virus is spread by the discharge from the blisters and by the saliva of infected animals. Animals may become infected by contact with an infected animal, contaminated animal parts, or contaminated objects, such as farm equipment. The virus can subsist in fodder, water, and on surfaces for up to one month, depending upon weather conditions. Under certain climatic conditions wind can also spread the virus. Animals that do not become sick from the virus, such as dogs and horses, may come in contact with the virus and carry it to susceptible animals or contaminate livestock facilities or equipment. People wearing contaminated clothing or footwear or who use contaminated equipment can also pass the virus on to other animals.

Foot-and-mouth disease is one of the most contagious of all viruses, and it is difficult to control its spread once an infected animal has been identified. Animal health officials debate the best method to halt the spread of the disease. The traditional method has been to destroy infected herds and to isolate the affected area so that the virus cannot spread. But in larger outbreaks involving hundreds of farms, this approach sometimes fails.

An alternative method is to use vaccines to control outbreaks. Long-term vaccination programs, in which animals are routinely immunized, and emergency vaccination programs initiated at the outset of a new outbreak, are considered highly controversial because their effectiveness is questionable and they pose both economic and practical problems. Opponents of vaccination programs argue that the cost of vaccines is exorbitant. A vaccine requires a primary vaccination with a booster shot each month for six months. Many farmers find it less expensive to slaughter animals when outbreaks occur than to routinely vaccinate. Moreover, existing laboratory tests are unable to distinguish between an animal that has been immunized and one that actually has the disease. This makes it difficult for livestock and meat exporters to prove that their animal products are not diseased, severely limiting agricultural trade. Another problem with vaccines is that there are at least seven strains of the virus that cause foot-and-mouth disease. An animal that is immunized for one strain is not protected from infection by another strain. Opponents of vaccines also argue that vaccines have not been proven effective and note that vaccinated livestock in Saudi Arabia came down with the disease.

Advocates of vaccines counter that despite its flaws, long-term vaccination can achieve widespread protection in livestock and also lower the risk of infection. They argue that when outbreaks do occur, the use of emergency vaccination, coupled with animal destruction, would be a superior approach to handling the disease than animal destruction alone. In addition, some scientists believe they are close to developing new forms of laboratory tests that can identify immunized animals from those carrying the disease. These tests would help exporters prove that their animals and animal products are disease-free, thereby lessening the damage to economic trade. Scientists are also working to develop a genetically engineered vaccine that advocates say would prove more effective than current vaccines.

Foot-and-mouth disease occurs around the world, most commonly in Asia, Africa, the Middle East, and South America. North America, Central America, Australia, New Zealand, Chile, and some countries in Europe have not had outbreaks in the last 50 years. The United States has experienced nine outbreaks. The most serious occurred in 1914, affecting 22 states and the District of Columbia. The last outbreak occurred in California in 1929. The disease has not been seen in Canada since 1952. In 1967 and 1968 an epizootic in the United Kingdom led to the slaughter of more than 430,000 animals to control the disease. Since 1995 extensive outbreaks have occurred in such varied geographic locations as Greece, Saudi Arabia, South Africa, Taiwan, and the United Kingdom.

A February 2001 outbreak in the United Kingdom resulted in the destruction of more than 1 million animals by the end of March, when the epizootic had yet to peak. Because the virus can be destroyed by disinfectants, many local governments in the United Kingdom required that any objects that could have been exposed to the virus, including shoes, automobile tires, and farm equipment, be disinfected before leaving or entering a particular area. Many affected areas of the British countryside were closed to nonessential foot and motor vehicle traffic, harming Britain’s tourist industry.

To prevent the disease from occurring in the United States, the United States Department of Agriculture (USDA) bans the import of animals and animal products from known infected areas. The USDA also strictly monitors all ports of entry to the United States, requiring passengers who have traveled in affected areas to disinfect their shoes. They also search luggage and cargo for the presence of animal products that could spread the disease.