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Foot and Mouth Disease

Routes Of Infection, Vaccination

Foot and mouth disease is caused by a particular type of virus. The disease affects cloven hooved animals; that is, animals with hooves that are split into two main segments. Examples of domestic cloven hooved animals include cattle, sheep, pigs, and goats. Wild cloven hooved animals that are susceptible to foot and mouth disease include elephants, hedgehogs, and rats.

Foot and mouth disease occurs all over the world. In parts of Asia, Africa, the Middle East, and South America, foot and mouth disease is common to the point of being a continual occurrence among various livestock herds. In other areas of the world, stringent control and inspection measures have made outbreaks infrequent. For example, there has not been an outbreak of foot and mouth disease in domestic animals in the United States since 1929. Canada last experienced an outbreak in 1952, and Mexico in 1954.

Other developed countries have been less fortunate. Outbreaks have occurred in Britain periodically since 1839. An outbreak in 1864–1866 devastated cattle herds throughout Britain, prompting legislation governing the transport and export of cattle. Outbreaks in the 1910s and from 1922–1924 saw slaughter introduced as an attempt to limit the spread of the disease. This control measure has been controversial ever since its implementation, because herds that may not be infected are often ordered destroyed.

In 1967–1968, over 400,000 domestic animals were slaughtered in an attempt to limit the spread of another outbreak. The latest large outbreak occurred in England beginning on February 20, 2001. The outbreak was declared over on January 14, 2002. In between these dates, 2030 cases were confirmed, and over 3,900,000 cattle, sheep, pigs, and goats had been slaughtered in England and Western Europe in order to contain the outbreak.

A cow and her calf stand drooling from hoof-and-mouth disease. © Reuters NewMedia Inc./Corbis. Reproduced by permission.

The virus that is responsible for the disease is a member of the viral family called Picornaviridae. Specifically, the virus is a member of the genus called Aphthovirus. A genus is a more detailed grouping of organisms based on common characteristics. The virus contains ribonucleic acid (RNA) as its genetic material. When the virus infects host cells, the RNA is used to make deoxyribonucleic acid (DNA), using the host's genetic replicating processes. The viral DNA then forms the template for the production of viral RNA, which is packaged into new viral particles and released from the host cells.

This infectious process is destructive for the host cells that have been housed the virus. Typically, an infection is apparent as blistering in the mouth and feet. Hence, the name of the disease. The blisters cause the feet to become very tender and sore, so that animals have difficulty walking. Often an infected animal will suddenly become lame. Other symptoms of infection include slobbering and smacking of the lips, fever with shivering, and reduced milk production.

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