1. Foot and mouth disease virus is named after the main symptoms of the highly infectious disease it causes in cloven hoofed animals (ungulates) such as cattle, sheep and pigs. In addition, these viruses can also infect elephants, rats, and hedgehogs, but not horses.
2. The symptoms of foot and mouth disease are fever, followed by the development of blisters (vesicles) chiefly in the mouth and on the feet of the animals, hence the name. Affected animals suffer weight loss from which they do not recover for several months, and in cows, milk production can decline significantly.
3. Foot and mouth disease is caused by a Picornavirus, which is one of the most diverse (more than 200 serotypes) virus families. FMDV was one of the first ever viruses to be recognized, by Loeffler and Frosch 1898. The large Picornavirus family is divided into a number of genera and the foot and mouth disease viruses belong to the Aphthovirus genus (from the Greek aphtha, meaning vesicles in the mouth). Other Picornaviruses include poliovirus and rhinoviruses, one of the sources of the common cold.
4. Picornaviruses are very small even for viruses, with a diameter of approximately 27 nm and a genome consisting of about 8,500 nucleotides of single-stranded RNA, one of the smallest virus genomes known. On entering a host cell, the virus genome acts as messenger RNA and virus proteins are translated in the cytoplasm. Some of these proteins make up new virus particles and others serve as enzymes which replicate the RNA genome of the virus, allowing new particles to assemble and be released from the cell.
5. The Aphthoviruses are quite distinct from other Picornaviruses. They are sensitive to acidic pH, meaning that they cannot pass through the acid conditions of the stomach to infect the gut. They are also antigenically very variable, with seven serotypes, (A, O, C, SAT1, SAT2, SAT3, Asia1) and more than 60 subtypes. The location of antigenic sites on the surface of the virus capsid (protein shell) is quite different from other Picornaviruses.
6. Serotype O, the most prevalent of the seven serotypes of FMDV, occurs in many parts of the world. A pandemic type O strain, Pan-Asia, was first identified in northern India in 1990 and spread westwards into Saudi Arabia during 1994 and, subsequently, throughout the Near East and into Europe in 1996. In February 2001, it spread to the UK, possibly from South Africa, and the UK was only finally declared officially free from FMDV again in January 2002, 11 months after the beginning of this outbreak.
7. Foot and mouth disease has an incubation period of 2-14 days before symptoms appear. The virus can survive in dry faecal material for 14 days in summer, in slurry for six months in winter, in urine for 39 days and on the soil for up to 28 days. Some infected animals remain asymptomatic carriers of the disease and can then transmit the disease to other animals.
One of the great problems with foot and mouth is that the symptoms of the disease is are indistinguishable (particularly in pigs and sheep) from a number of other diseases such as vesicular stomatitis (caused by a Rhabdovirus), swine vesicular disease (caused by another Picornavirus) and vesicular exanthema of pigs (caused by a Calicivirus).
8. Vaccination against FMDV is difficult because there are seven serotypes of the virus and a vaccine for one serotype does not protect against any others. Because the killed vaccines used are not the most effective vaccines, vaccination only provides temporary immunity even against a single strain of the virus (Tough choice of kill or vaccinate. The Sunday Times, August 5, 2007).
9. Currently, the World Organisation for Animal Health recognizes countries to be in one of three disease states with regards to foot and mouth: disease present, disease-free with vaccination, and disease-free without vaccination. Countries that are designated disease-free without vaccination have the greatest access to export markets, so many developed nations, including the UK and the United States work hard to maintain disease-free without vaccination status. Routine, preventative vaccination is banned under EU law, thus allowing the EU to maintain the highest FMDV status under international trade rules.
10. Can humans catch foot and mouth? Yes – but only just.
Humans can be infected with foot-and-mouth disease through close contact with infected animals, but this is extremely rare and human infections are not fatal. Because FMDV is sensitive to stomach acid, it cannot infect humans via consumption of infected meat or milk, and the UK Food Standards Agency considers that foot and mouth disease has no implications for the human food chain. The last human case reported in Britain occurred in 1966, during an epidemic of foot and mouth disease (Foot and mouth disease: the human consequences 2001 BMJ 322: 565-566). There is one report from 1834 of three veterinarians acquiring the disease from deliberately drinking raw milk from infected cows. Foot and mouth disease should not be confused with the human disease hand, foot, and mouth disease, an unrelated and usually mild virus infection of infants and children.