Foot-and-mouth disease (FMD) is the most devastating disease of farm animals in the world. It can destroy food supplies and farmers' livelihoods almost overnight because of the wide number of cloven-hoofed animals that are affected, which include cattle, pigs and sheep. In the developed world this disease is a serious matter for the farmer, but causes little concern to the consumer. But in developing countries foot-and-mouth can have a much wider and far more serious impact.
Foot-and-mouth disease can occur anywhere in the world, though in many countries it is now sporadic. It is regularly found in parts of South America, Central and Eastern Africa, the Middle and Far East. Some animals such as the African buffalo can carry the virus for up to five years.
The disease is caused by a very small RNA virus, which is 28nm in diameter (2.8 millionths of a millimetre). There are seven distinct serotypes of the virus (see below). Whilst they all look alike, each serotype stimulates a different immune response. Immunity to one serotype does not protect against another, and this is a big problem when it comes to making vaccines.
Serotypes foot-and-mouth disease virus
- SAT* 1, 2, 3
- Asia 1
* Southern African Territories
The most common method of transmission is contact between infected and susceptible animals. However, infected pigs can release up to 400 million infectious units each day in their breath. Under humid conditions, the virus survives well in the atmosphere. This makes the wind an important mechanisms for FMD transmission, particularly in northern Europe.
The incubation period is typically 2 to 14 days, but mostly 3 to 5 days. As few as 10 infectious units of foot-and-mouth disease virus are enough to infect a cow.
The virus can travel 60 km downwind on land during an outbreak, and up to 200 km over water
Controlling the disease
There is no treatment for infected livestock. Countries where FMD is common suffer the economic and social consequences of reduced milk and meat production as well as embargoes on their exports of animal products. They use vaccination to control the disease, but this is also expensive. Countries free from the disease are obliged to spend lots of money on safety measures to keep the virus out. Eradication of virus is achieved by the slaughter of affected animals and those in contact, together with the control of animal movements in the area. The eradication of the disease requires active disease surveillance, rapid reporting of suspected cases and fast, reliable diagnosis so that control measures can be put into action without delay.
Vaccination of healthy animals is possible but immunity is virus type-specific, there is no cross-protection, and it is short-lived. There is also the danger that vaccinated animals, although protected against developing the disease, may become carriers if exposed to new infections of the virus.
Countries affected by foot-and-mouth disease, particularly developing countries, benefit from expert advice on FMD. This advice is based on laboratory research which shows the most suitable vaccine that should be used during each particular outbreak and details of the outbreak virus itself, which can help control its spread or re-introduction. Considerable experience at The Pirbright Institute is available from successful control programmes in other countries.
The World Reference Laboratory for FMD at IAH provides a diagnostic service to the world and maintains a global surveillance for the disease to warn of its presence and help prevent its spread to neighbouring countries and trading partners.
Research at IAH using samples of FMDV from Africa, Asia and South America has provided a unique insight into the evolution and natural history of the virus in its natural environment. The information has helped to show how the virus survives by causing persistent infections in cattle and buffalo and how it evades the immune response of its infected host.
The seriousness of FMD ensures that all outbreaks are recorded and samples collected. These are received and catalogued at the IAH into a unique library, unequalled for any other animal virus. This continually provides our scientists with new insights into the disease, but at the same time posing new questions.
Hope for the Future
Research continues to look for new and improved diagnostic techniques. One goal is to develop a test that can be taken out of the laboratory and on to the farm in order to speed up the effects of any control measures that are put in place when FMD is suspected.
There is a lot that could be done to improve FMD vaccines, such as making them more stable in the hot, tropical, climates where they are frequently needed. Current vaccines only provide six month's protection at best, but if this could be increased to one year the cost of vaccination would be reduced significantly. Advances in molecular biology hold the promise for better, cheaper, and more stable vaccines.