Foot-and-Mouth Disease

Foot-and-Mouth Disease, contagious febrile disease of animals. It is caused by a virus that belongs to the family Picornaviridae, and affects cloven-hoofed animals such as cattle, pigs, sheep, goats, and deer, often causing epidemics. It is from the same family as the virus that causes hand- and foot-and-mouth disease in humans. There have been a few reports of possible human infections with foot-and-mouth disease virus, but the symptoms have been very mild and non-life threatening. The disease in animals is characterized by a sudden rise in temperature, followed by an eruption of blisters involving the mouth, on the lips, gums, and tongue; on the feet, in particular between the digits and around the skin at the top of the hooves; and in the nostrils. Lameness, excessive salivation, and frequent smacking of the lips accompany the eruption. The blisters grow larger and then break, exposing raw, eroded surfaces. Eating becomes difficult and painful, and because the soft tissues under the hoof are inflamed, the animal invariably becomes very lame and may even shed its hooves. Livestock lose much weight, and dairy cattle and goats give less milk. The disease often kills very young animals, with young lamb mortality as high as 80 per cent in some cases, and causes pregnant females to abort. The crippling effect is extremely serious where oxen are used as draught animals.

Foot-and-mouth disease is endemic in a number of countries in the world, and the disease was reported in 36 countries worldwide in the 14 months to February 2002. The virus has seven main serotypes (A, C, O, Asia 1, and SAT–1, –2, and –3), with a spectrum of strains within each serotype, and all cause contagious infection. The O-type Pan Asia strain of the virus, for example, was first identified in India in 1990, and subsequently has spread east to Nepal, China, North Korea, Japan, and Taiwan, as well as west to Saudi Arabia, Turkey, Greece, Bulgaria, and South Africa. The extent of the spread is shown by Japan now having foot-and-mouth disease for the first time in almost 100 years.

The virus is a major problem to livestock raisers, as well as the meatpacking, dairy, leather, and wool industries. The virus is present in all body fluids in the incubation stage (two to four days before first signs) and during the clinical stage. Most of the virus is in the fluid from the vesicles and saliva. It is also spread by animal to animal, or in spray form (by aerosol), but humans and vehicles can carry the virus that can survive for weeks on wool, hay, straw, and manure. The diagnosis is usually from the clinical signs, supported by laboratory examination of tissue from the animals, both to identify the virus and carry out antibody tests. This can take up to 96 hours, but an early indication of the tests being negative may be possible within 24 hours.

The control of the disease is by rapid slaughter of affected and in-contact animals in countries that wish to be free of the disease, or where it is endemic, the use of a vaccination programme. Considerable progress has been made towards developing an effective vaccine against foot-and-mouth disease, but the present vaccines have limited efficacy. To successfully vaccinate animals it would be necessary to have a bank of many different vaccines available. Even if there were a vaccine it would take weeks to take effect, and the current vaccines do not treat animals infected with foot-and-mouth disease virus. In addition, in the context of international trade rules, and the attitude of consumers to eating meat or drinking milk from vaccinated animals, there would be an impact on international trade if the vaccine were used. Also, the cost of vaccinating all susceptible animals would be significant. The vaccines currently available would not eradicate the disease. Consequently, the slaughter of all exposed animals, as well as restrictions on the movement of animals in areas affected, is the countermeasure to foot-and-mouth disease that is presently effective.

During the 2001 outbreak in Britain that lasted from February to September, for example, in the costliest outbreak in modern times, the UK government responded by aiming to have a rapid cull of all animals susceptible to the disease on infected premises within 24 hours, and all susceptible animals on farms sharing a boundary with infected premises within 48 hours. In addition, premises had their livestock slaughtered if there was evidence of dangerous contact, and the slaughter of animals “under suspicion” took place where there were good grounds to suspect the disease even though it could not be confirmed without laboratory tests. By the end of the outbreak there had been a total of 2,030 reported cases, resulting in the culling of 4.145 million animals, of which 3.412 million were sheep, 592,000 cattle, 141,000 pigs, 2,000 goats, 1,000 deer, and 1,000 other animals. There was also the slaughter of a further 2 million animals under a welfare disposal scheme.

A problem with such a policy is the consequences for rare breeds where some breeds could be critically endangered or the biodiversity reduced. This was of some concern in the UK where there are “hefted” sheep on the hills which required some three generations to introduce the “knowledge” of the hill to the flocks, for example, the grazing boundaries, and where on the hill to find food and shelter at different times of the year. There was real concern for wildlife collections in the UK. That the consequences were not as severe as expected had much to do with the heightened level of bio-security. This reinforces the need to consider the movements of animals between farms and throughout the country. In the UK outbreak it was the consequence of the disease possibly being present and undetected in the sheep at a time of the year (February 2001) when there was thought to be as many as 2 million sheep movements in three weeks.