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Aphthovirus (causes foot-and-mouth disease)

(Life; viruses; Family: Picornaviridae)

Foot and Mouth Disease

Foot-and-mouth disease is one of the most contagious animal diseases and causes death mainly to young animals through inflammation of the heart muscle (i.e. myocarditis). It infects animals in the families Bovidae (cattle, sheep, goats, antelope) and Suidae (pigs, warthogs).  Symptoms include the formation of blisters in the mouth and between the claws, hence the name. People can be infected through skin wounds or the mucous membranes in the mouth by handling diseased stock, handling the virus in the laboratory, or by drinking infected milk, but not by eating meat from infected animals. However, infection of humans is temporary and mild and foot-and-mouth disease is not considered a public health problem. 

Transmission. Infection can spread all too easily through direct or indirect contact. This can be through movement of humans, animals, vehicles and implements, and through the air, especially in temperate zones (up to 60 km overland and 300 km by sea). Cattle are mainly infected by inhalation, often from pigs, which excrete large amounts of virus through their breathing and are considered highly important in disease spread. Aphthovirus, which causes this disease, is in the same family of viruses as the Common Cold viruses (Rhinovirus) and you know just how easily they can spread! Newly infected animals start spreading the virus before symptoms appear so it is often difficult to control this disease before it has spread too far. African Buffalo are important carriers of foot-and-mouth disease. Recovered cattle may be carriers for 18 to 24 months; sheep for 1 to 2 months, while pigs are not carriers. 

Distribution. Foot-and-mouth disease is endemic in parts of Asia, Africa, the Middle East and South America with sporadic outbreaks in free areas.  Foot-and-mouth disease was last reported in 1929 in the U.S.A., 1952 in Canada, and 1954 in Mexico. There have been a notably high number of outbreaks recently, the most publisised being that in the UK.  Foot-and-mouth disease was reported from the following countries from 1999 to March 2001: Argentina, Bhutan, Brazil, Colombia, Egypt, France, Georgia, Greece, Iran, Israel, Japan, Kazakhstan, Korea, Kuwait, Malawi, Malaysia, Mauritania, Mongolia, Namibia, Peru, Philippines, Russia, Saudi Arabia, South Africa, Swaziland, Taipei China, Tajikistan, Turkey, United Kingdom / Great Britain, Northern Ireland (isolated case stemming from outbreak in England), Uruguay, Zambia and Zimbabwe (information from OIE). The outbreak in KwaZulu-Natal in South Africa was first detected on 12 September 2000.

Symptoms. Fever (pyrexia), lack of appetite (anorexia), reduction in milk production for 2-3 days.  The blisters that form in the mouth and nasal cavities make the animal smack its lips, grind its teeth and drool. The blisters that form between the claws cause lameness, stamping and kicking of feet. In sheep and goats the blistering is less pronounced. 

Prevention and Control. 

  • Animal movement control through construction of border fences and surveillance of trucks, etc where roads and railways pass through these borders.
  • Slaughter of infected, recovered, and susceptible contact animals.
  • Disinfection of premises and infected materials (implements, cars, clothes, etc.).
  • Destruction of cadavers and susceptible animals products in the infected areas.
  • Quarantine measures. The incubation period is 2-21 days (average 3-8 days) so animals passing out of infected areas would presumably need to be held in quarantine for at least 14 days before the disease could be reliably tested.  
  • Vaccination. Tests for foot-and-mouth disease involve testing for antibodies to this disease and as both the real disease and the vaccination lead to the build up of antibodies, vaccinated animals are excluded because of the risk of bringing in animals that actually are infected. However, new tests are currently being developed that will enable differentiation of vaccinated and infected livestock.  The rationale behind this method is as follows: (1) the vaccination involves injecting the animal with inactivated viral particles made up of structural proteins; (2) the animal develops antibodies against these structural proteins; (3) the live viral particles include structural proteins as well as non-structural proteins which are produced during viral replication; (4) the animal develops antibodies against both these forms of proteins when infected by the live virus; (5) the test therefore distinguishes each of these main types of antibodies - if only the antibodies against structural proteins are detected, then there can be certainty that it is vaccinated and not infected. 

Links

References

  • Anon. 2001. Delays allowed foot-and-mouth epidemic to sweep across Britain. Nature 410: 501.

  • Anon. 2001. Standards needed for foot-and-mouth tests. Nature 410: 1012.

Text by Hamish G. Robertson  


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