The virus may be cultivated in bovine or pig kidney cells, or bovine tongue epithelium. It is stable between pH 6 and pH 8, is rapidly destroyed by sunlight, remains for many months at 4-7°C, and for years when frozen. The virus can remain infective for 20 weeks on straw, is rapidly destroyed in meat, but may persist for up to 6 months in bone marrow and 4-5 months in lymph nodes.
Infection takes place by the respiratory and oral routes and through abrasions on the skin. Virus multiplies in the throat or at the point of entry and then in other parts of the body. Vesicles (blisters) develop, particularly on the coronary band and tongue. Virus is shed by aerosol within 24 hours of the first signs. Vesicles rupture and if uncontaminated, heal rapidly. Those on the feet may result in destruction of growing horn and loss of the hoof. Immunity develops within 3-7 days of the clinical signs, lasts only 6 months but only protects fully against the virus subtype involved.
Foot and mouth disease (FMD) is a severe, highly contagious viral disease of livestock that has a significant economic impact. The disease affects cattle, swine, sheep, goats and other cloven-hoofed ruminants. It is a transboundary animal disease (TAD) that deeply affect the production of livestock and disrupting regional and international trade in animals and animal products.
The disease is estimated to circulate in 77% of the global livestock population, in Africa, the Middle East and Asia, as well as in a limited area of South America. Countries that are currently free of FMD without vaccination remain under constant threat of an incursion. Seventy-five percent of the costs attributed to FMD prevention and control are incurred by low income and lower-middle income countries.
The impact of smallholder tobacco commercialisation on food security in Southern Africa
Africa and Eurasia are the regions which incur the largest costs, accounting for 50% and 33% of the total costs respectively. FMD is caused by an Aphthovirus of the family Picornaviridae, seven strains (A, O, C, SAT1, SAT2, SAT3, and Asia1) are endemic in different countries worldwide. Each strain requires a specific vaccine to provide immunity to a vaccinated animal. Its prevention is based on the presence of early detection and warning systems and the implementation of effective surveillance among other measures. FMD is the first disease for which the OIE established an official list of disease-free countries which can be officially recognised as free of the disease either in their entirety or in defined zones and compartments.
FMD is found in all excretions and secretions from infected animals. Notably, these animals breathe out a large amount of aerosolised virus, which can infect other animals via the respiratory or oral routes.
The virus may be present in milk and semen for up to 4 days before the animal shows clinical signs of disease.
The significance of FMD is related to the ease with which the virus can spread through any or all of the following:
- infected animals newly introduced into a herd (carrying virus in their saliva, milk, semen, etc.);
- contaminated pens/buildings or contaminated animal transport vehicles;
- contaminated materials such as hay, feed, water, milk or biologics;
- contaminated clothing, footwear, or equipment;
- virus-infected meat or other contaminated animal products (if fed to animals when raw or improperly cooked);
- infected aerosols (spread of virus from an infected property via air currents).
Animals that have recovered from infection may sometimes carry the virus and initiate new outbreaks of the disease.
