FOOT-AND-MOUTH DISEASE.

Foot-and-mouth disease (FMD) is a severe, highly communicable and economically devastating viral disease of cattle and swine. It also affects sheep, goats, deer, and other clovenhoof ruminants. Many affected animals recover, but the disease leaves them debilitated. FMD causes severe losses in the production of meat and milk. The disease does not effect food safety or humans. Other susceptible species include hedgehogs, nutria, rats, armadillos, elephants, capybaras, and mice. FMD is not recognized as a zoonotic disease. The disease is characterized by fever and blisterlike lesions followed by erosions on  the tongue and lips, in the mouth, on the teats, and between the hooves. Because it spreads widely and rapidly and because it has grave economic as well as clinical consequences, FMD is one of the animal diseases that livestock owner dread most.
In 350 B.C., Aristotle mentioned a cattle plague that could have been FMD or rinderpest. In 1546, the Italian physician Fracastorius gave the first clear description of the disease. For the next two centuries, the number of outbreaks in Europe increased. In 1897, Foeffler and Frosch demonstrated for the first time that FMD was caused by a filterable agent. Before the availability of an FMD vaccine, when an outbreak of the disease occurred, European farmers would deliberately spread it to other animals in the herd by rubbing the tongues of infected cattle with a rough towel and then rubbing the same towel on the tongues of healthy cattle.
Farmers did this to shorten the course of the disease in their herds and provide immunity against the next outbreak of FMD. But observers noted that animals that recovered were not always protected against future outbreaks of FMD. This observation led to the demonstration in 1922 of type 0 (Oise valley) and type A (Allemagne) in France. In 1926, a third serotype was recognized and named C in anticipation that the previously recognized serotypes would be renamed to allow naming of additional serotypes, A, B, C, etc. The SAT subtypes were described between 1934 and 1948, and Asia 1 was isolated in Pakistan in 1954. The United States has experienced nine distinct epizootics; the most serious occurred in 1914, invading 22 states and the District of Columbia. The latest outbreak, which occurred in California in 1929, was quickly controlled.

The United Kingdom Ministry of Agriculture, Fisheries and Food (MAFF) confirmed on February 20, 2001 an outbreak of foot and mouth disease, virus type O, in Essex County, England.
The disease was confirmed on two premises in close proximity; a slaughter plant and a nearby farm. On February 22, a third case of FMD was confirmed at a cattle farm inside the 8-kilometer exclusion zone. On February 23, MAFF confirmed two additional cases; one on a farm in Essex county, and one on a hog farm located 300 miles north of Essex. This latter farm had supplied hogs to the slaughter establishment mentioned above. The virus was confirmed as the same South East Asian strain as that found in Japan and Korea and associated with swill in South Africa. Prior to this outbreak, the UK was considered by the USDA to be free of FMD. The last outbreak of FMD in the UK was in 1981.
The FMD disease is caused by a virus. The FMD virus (FMDv) is a member of the genus Apthovirus in the family Picornaviridae. The virion is a small (23-nm) single-stranded RNA virus. The virus survives in lymph nodes and bone marrow at neutral pH, but destroyed in muscle when in pH<6.0 i.e. after rigor mortis. The virus can persist in contaminated fodder and the environment for up to one month, depending on the temperature and pH conditions. There are seven serotypes of FMD virus, O, A, C, Asia 1, SAT 1, SAT 2 and SAT 3, distributed throughout the world and many subtypes of the FMD virus. Immunity to one type does not protect an animal against other types.
Serotype O is the most widely distributed, being endemic in many South American, African and Asian countries, affecting all susceptible species. It has caused recent outbreaks in Italy (1993), Greece (1994 and 1996), Bulgaria (1991, 1993 and 1996), Georgia (1997), Armenia (1996) and the southern republics of the former Soviet Union, Taiwan (1997), Russia (1995), and Philippines (major outbreaks in 1996). Certain strains of serotype O appear particularly adapted to a particular host species. Within serotype O there are groups of strains (genotypes) that are associated with particular areas of distribution, and species preference. The Middle East type O is well adapted to sheep and cattle (possibly due to the small number of pigs in the region), whereas the Far East type O is responsible for the major outbreaks in pigs in that region. In areas where there are outbreaks in pigs and cattle (e.g., Vietnam), the strains causing disease in each species are easily distinguishable by nucleotide sequencing.
Serotype A is present in South America, Africa and Asia, and in 1996 caused outbreaks in Albania, the former Yugoslav Republic of Macedonia and Serbia, following the introduction of infected meat products. It is characterised by local outbreaks which appear self-limiting, even though the strains of serotype A causing the outbreak may be outside the protection provided by available vaccine strains. The antigenic diversity of strains of serotype A is much greater than that seen within the other serotypes. Four antigenically new strains of serotype A have been identified during 1996 and 1997 in Iran, Malaysia, Thailand, Eritrea and West Africa. The new serotype A strain in Iran spread into Turkey during 1997 and threatened to enter Europe through Turkish Thrace.
Serotype C is found in South America, Africa and Asia. It is characterised by sporadic outbreaks and subsequent disappearance from an area for a variable time. In recent years, only in the Philippines has it been associated with a continuous series of outbreaks since its introduction there in 1976. However, there have been no recorded outbreaks in the Philippines due to type C since 1995.
Serotype Asia 1. The Asia 1 serotype is restricted to the Middle and Far East. It rarely causes outbreaks in pigs, and is mainly seen in the cattle and Asian buffalo populations. This serotype has been found circulating in association with serotype O and/or serotype A, and its presence in diagnostic samples may be missed.
SAT Serotypes (South African Territories). The SAT viruses are restricted to Africa, although they have caused occasional outbreaks in the Middle East which have never persisted. The SAT 1 and SAT 3 serotypes rarely cause outbreaks in cattle and are usually only found in the African buffalo populations. The SAT 2 serotype is the most frequently found cause of FMD in cattle in sub-Saharan Africa. It can maintain itself for many years, particularly in the zebu breed of cattle. Other wildlife species, particularly impala, have been implicated in the transmission of SAT serotypes between buffalo and cattle. The FMD viruses can be spread by animals, people, or materials that bring the virus into physical contact with susceptible animals. An outbreak can occur when:
• People wearing contaminated clothes or footwear or using contaminated equipment pass the virus to susceptible animals.
• Animals carrying the virus are introduced into susceptible herds.
• Contaminated facilities are used to hold susceptible animals.
• Contaminated vehicles are used to move susceptible animals.
• Raw or improperly cooked garbage containing infected meat or animal products is fed to susceptible animals.
• Susceptible animals are exposed to materials such as hay, feedstuffs, hides, or biologics contaminated with the virus.
• Susceptible animals drink common source contaminated water.
• A susceptible cow is inseminated by semen from an infected bull.
Once an animal becomes infected, the primary mode of spread is then via respiratory aerosols. Other important means of spread are direct and indirect contact. In an outbreak of FMD, the three primary hosts transmit the disease as follows:
• Sheep act as maintenance hosts.
• Pigs act as amplifiers.
• Cattle act as indicators.

When sheep or goats become infected with FMDv, the disease may not be diagnosed for a considerable time because signs and lesions can be very mild. During this time, however, the animals will be producing infectious aerosols, contaminating fomites, and spreading the virus by contact. FMD in pigs spreads very rapidly because pigs produce 30 to100 times as much virus in aerosols as do sheep or cattle. An infected pig can produce a hundred million infectious doses per day.
When cattle are infected with FMDv, signs and lesions usually develop more rapidly and are more severe than lesions in pigs, sheep, or goats. If cattle, sheep, and pigs are exposed together, cattle will usually get sick first. Possibly, cattle are subject to increased exposure due to their greater pulmonary tidal volume. Some strains of FMDv seem to affect particular species more than other strains. For example, some strains affect pigs but not cattle. In South America, mature cattle have had clinical signs of FMD while sheep in an adjacent pasture were normal. Vesicles (blisters) followed by erosions in the mouth or on the feet and the resulting excessive salivating or lameness are the best known signs of the disease. Often blisters may not be observed because they easily rupture, leading to erosions. Some of these other signs may appear in affected animals during an FMD outbreak:
• Temperatures rise markedly, then usually fall in about 2 to 3 days.
• Ruptured vesicles discharge either clear or cloudy fluid and leave raw, eroded areas surrounded by ragged fragments of loose tissue.
• Sticky, foamy, stringy saliva is produced.
• Consumption of feed is reduced because of painful tongue and mouth lesions.
• Lameness with reluctance to move is often observed.
• Abortions often occur.
• Milk flow of infected cows drops abruptly.
• Conception rates may be low.
Meat animals do not normally regain lost weight for many months. Recovered cows seldom produce milk at their former rates. FMD can lead to myocarditis (inflammation of the muscular walls of the heart) and death, especially in newborn animals. FMD can be confused with several similar, but less harmful, diseases, such as vesicular stomatitis, bluetongue, bovine viral diarrhea, and foot rot in cattle, vesicular exanthema of swine, and swine vesicular disease. Whenever mouth or feet blisters or other typical signs are observed and reported, laboratory tests must be completed to determine whether the disease causing them is FMD. While the disease is widespread around the world, North America, Central America, Australia, New Zealand, Chile, and some countries in Europe are considered free of FMD. Various types of FMD virus have been identified in Africa, South America, Asia, and part of Europe.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 the United States. Animals and animal byproducts from areas known to be infected are prohibited entry into the United States. Livestock animals in the United States are highly susceptible to FMD viruses. If an outbreak occurred in the United States, this disease could spread rapidly to all sections of the country by routine livestock movements unless it was detected early and eradicated immediately. If FMD were to spread unchecked, the economic impact could reach billions of dollars in the first year. Deer and wildlife populations could become infected rapidly and could be a source for re-infection of livestock.

From 'Van Nostrand’s Scientific Encyclopedia. — 10th ed.- edited by Glenn D.Considine, Published by John Wiley & Sons, Inc., Hoboken, New Jersey, USA, 2008, p. 2057-2059. Adapted and illustrated to be posted by Leopoldo Costa.