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Foot-and-mouth disease

Foot-and-mouth disease (FMD) is one of the most contagious animal diseases - as little as 10 virions are needed in order to infect an animal. The virus infects cloven hoofed (two-toed) mammals such as cattle, sheep, goats, pigs and has also been reported in 70 plus species of wild artiodactyls, including bison, giraffes, Indian elephants, and several species of deer and antelope. Intensively reared animals are more susceptible to the disease than traditional breeds.

 It is a common infection that causes mouth ulcers and spots on the feet, mouth, nose, muzzle and teats causing lameness and salivation. The severity of clinical signs will depend on the strain of virus, the age and species of animal. It can also be responsible for fevers, a reduced appetite due to painful blisters in the mouth, causing a reduction in milk yield, weight loss and abortions.

The disease is rarely fatal in adult animals but there is often high mortality in young animals due to myocarditis or caused by lack of milk when the dam is infected by the disease. In a susceptible population, morbidity approaches 100%. While the majority of affected animals recover, the disease often leaves them weakened and debilitated.

FMD is endemic in several parts of Asia, most of Africa and the Middle East and cause huge economic losses when an outbreak occurs in countries free from FMD. The disease spreads very quickly if not controlled. Infected animals notably breathe out a large amount of aerosolised virus, which can infect other animals via the respiratory or oral routes. The disease is therefore passed on to healthy animals through mostly direct contact with infected animals but indirect contact with contaminated objects (fomites) such as vehicles, clothing, footwear, bedding etc. can also spread the disease.

The virus can persist in contaminated fodder and the environment for up to one month, depending on the temperature and pH conditions. FMD is found in all excretions and secretions from an infected animal. Contaminated food or aerosols can transmit the virus as the virus can be carried by the wind and travel fairly large distances, even over sea. Unfortunately, animals that have recovered from infection may serve as carriers of the virus.

The organism which causes FMD is an aphthovirus of the family Picornaviridae. FMDV is a non-enveloped virus with a single stranded RNA genome. There are seven types/strains (serotypes) (A, O, C, SAT1, SAT2, SAT3, Asia1) that are subject to high mutation rates which constantly generate new FMDV variants. Each strain produce the same symptoms, distinguishable only in the lab and each require a specific vaccine type to provide immunity to a vaccinated animal. Immunity to one type does not protect an animal against other types.

The virus survives in lymph nodes and bone marrow at neutral pH, but is destroyed in muscle when pH is less than 6.0, i.e., after rigor mortis. The primary site of infection and replication of FMD is in the mucosa of the pharynx. The virus may also enter through skin lesions or the GI tract. Once distributed throughout the lymphatic system, the virus replicates in the epithelium of the mouth, muzzle, teats, feet, and areas of damaged skin. Vesicles then develop at the organs and rupture within 48 hr. More than 50% of ruminants that recover from illness and those that are vaccinated and have been exposed to virus can carry virus particles in the pharyngeal region for up to 3.5 yr in cattle, 9 months in sheep, and over 5 years in African buffalo. 

Treatment is not given to sick animals as they will recover on their own. However, because of the loss of production and the infectious state of the disease, infected animals are usually culled in intensive animal systems. Vaccination is used to reduce the spread of FMD or protect specific animals. Vaccines are also used in endemic regions to protect animals from clinical disease. FMDV vaccines must closely match the serotype and strain of the infecting strain. Unfortunately, there is no current universal FMD vaccine. However, the Pirbright Institute, the World and European reference laboratory for FMD is currently working on novel vaccines which may provide protection against multiple types.

FMD is one of the most difficult animal infections to control. Because the disease occurs in many parts of the world, there is always a chance of its accidental introduction into an unaffected country. The initial measures in the global strategy for dealing with FMD are early detection and warning systems and prevention measures in place according to OIE Guidelines for the Surveillance of Foot and Mouth Disease (OIE Terrestrial Animal Health Code). This contributes to monitoring the occurrence, prevalence and characterisation of FMD viruses.

FMD outbreaks are usually controlled by quarantines, export restrictions and movement restrictions, euthanasia of affected and in-contact animals, and cleansing and disinfection of affected premises, equipment and vehicles. Good biosecurity measures should be practiced on uninfected farms to prevent entry of the virus.

Researchers are trying to improve diagnostics and the understanding of the transmission and immune responses to infection to better prevent and treat the disease. The main objective is to find a universal vaccine which would provide protection against multiple serotypes of the virus.

FMD is a disease listed in the World Organization for Animal Health (OIE) Terrestrial Animal Health Code and must be reported to the OIE (OIE Terrestrial Animal Health Code). FMD is the first disease for which the OIE established an official list of free countries and zones with or without vaccination.

FMD is not recognised as a zoonotic disease – it is not readily transmissible to humans. Foot-and-mouth disease (FMD) is not to be mistaken for Hand, foot and mouth disease, a common human infection that causes mouth ulcers and spots on the hands and feet. This disease most common in young children – particularly those under 10 – but can affect older children and adults as well. The infection usually clears up by itself within 7 to 10 days without extensive medical care. The symptoms on both diseases are similar but the diseases are not related and caused by very different viruses.

 


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