Foot-and-mouth disease (FMD) or hoof-and-mouth disease (HMD) is an infectious and sometimes fatal viraldisease that affects cloven-hoofed animals, including domestic and wild bovids.[1][2] The virus causes a high fever lasting two to six days, followed by blisters inside the mouth and on the feet that may rupture and cause lameness.
FMD has very severe implications for animal farming, since it is highly infectious and can be spread by infected animals comparatively easily through contact with contaminated farming equipment, vehicles, clothing, and feed, and by domestic and wild predators.[3] Its containment demands considerable efforts in vaccination, strict monitoring, trade restrictions, quarantines, and the culling of both infected and healthy (uninfected) animals.
Susceptible animals include cattle, water buffalo, sheep, goats, pigs,[4][5] antelope, deer, and bison. It has also been known to infect hedgehogs and elephants;[3][6] llamas and alpacas may develop mild symptoms, but are resistant to the disease and do not pass it on to others of the same species.[3] In laboratory experiments, mice, rats, and chickens have been artificially infected, but they are not believed to contract the disease under natural conditions.[3]Cattle, Asian and African buffalo, sheep, and goats can become carriers following an acute infection, meaning they are still infected with a small amount of virus but appear healthy. Animals can be carriers for up to 1–2 years and are considered very unlikely to infect other animals, although laboratory evidence suggests that transmission from carriers is possible.[7][8]
Humans are only extremely rarely infected by foot-and-mouth disease virus. (Humans, particularly young children, can be affected by hand, foot, and mouth disease, an unrelated viral infection, which also affects cattle, sheep, and swine. While the two viruses are unrelated, they are often confused.[9])
The virus responsible for FMD is an aphthovirus, foot-and-mouth disease virus. Infection occurs when the virus particle is taken into a cell of the host. The cell is then forced to manufacture thousands of copies of the virus, and eventually bursts, releasing the new particles in the blood. The virus is genetically highly variable,[10] which limits the effectiveness of vaccination. The disease was first documented in 1870.
Signs and symptoms[edit]
The incubation period for FMD virus has a range between one and 12 days.[11][12] The disease is characterized by high fever that declines rapidly after two to three days, blisters inside the mouth that lead to excessive secretion of stringy or foamy saliva and to drooling, and blisters on the feet that may rupture and cause lameness.[4][13] Adult animals may suffer weight loss from which they do not recover for several months, as well as swelling in the testicles of mature males, and cows' milk production can decline significantly. Though most animals eventually recover from FMD, the disease can lead to myocarditis (inflammation of the heart muscle)[14] and death, especially in newborn animals. Some infected ruminants remain asymptomatic carriers, but they nonetheless carry the virus and may be able to transmit it to others. Pigs cannot serve as asymptomatic carriers.[15]
Subclinical Infection[edit]
Subclinical (asymptomatic) infections can be classified as neoteric or persistent based on when they occur and whether the animal is infectious. Neoteric subclinical infections are acute infections, meaning they occur soon after an animal is exposed to the FMD virus (about 1 to 2 days) and last about 8 to 14 days.[16] Acute infections are characterized by a high degree of replicating virus in the pharynx. In a neoteric subclinical infection, the virus remains in the pharynx and does not spread into the blood as it would in a clinical infection. Although animals with neoteric subclinical infections do not appear to have disease, they shed substantial amounts of virus in nasal secretions and saliva, so they are able to transmit the FMD virus to other animals. Neoteric subclinical infections often occur in vaccinated animals but can occur in unvaccinated animals as well.[7]
Persistent subclinical infection (also referred to as a carrier state) occurs when an animal recovers from an acute infection but continues to have a small amount of replicating virus present in the pharynx. Cattle, buffalo, sheep, and goats can all become carriers, but pigs cannot.[7][17] [18][19] Animals can become carriers following acute infections with or without symptoms. Both vaccinated and unvaccinated animals can become carriers.[20] Transmission of the FMD virus from carriers to susceptible animals is considered very unlikely under natural conditions and has not been conclusively demonstrated in field studies.
However, in an experiment where virus was collected from the pharynx of carrier cattle and inserted in the pharynx of susceptible cattle, the susceptible cattle became infected and developed characteristic blisters in the mouth and on the feet.[8] This supports the theory that while the likelihood of a carrier spreading FMD is quite low, it is not impossible. It is not fully understood why ruminants but not pigs can become carriers or why some animals develop persistent infection while others do not. Both are areas of ongoing study.
Because vaccinated animals can become carriers, the waiting period to prove FMD-freedom is longer when vaccination rather than slaughter is used as an outbreak-control strategy. As a result, many FMD-free countries are resistant to emergency vaccination in case of in outbreak out of concern for the serious trade and economic implications of a prolonged period without FMD-free status.[7]
Although the risk of transmission from an individual FMD carrier is considered to be very low, there are many carriers in FMD-endemic regions, possibly increasing the number of chances for carrier transmission to occur. Also, it can be difficult to determine if an asymptomatic infection is neoteric or persistent in the field, as both would be apparently healthy animals that test positive for the FMD virus. This fact complicates disease control, as the two types of subclinical infections have significantly different risks of spreading disease.[7]
Cause[edit]
Of the seven serotypes[21] of this virus, A, C, O, Asia 1, and SAT3 appear to be distinct lineages; SAT 1 and SAT 2 are unresolved clades.[22] The mutation rate of the protein-encoding sequences of strains isolated between 1932 and 2007 has been estimated to be 1.46 × 10−3 substitutions/site/year, a rate similar to that of other RNA viruses. The most recent common ancestor appears to have evolved about 481 years ago (early 16th century). This ancestor then diverged into two clades which have given rise to the extant circulating Euro-Asiatic and South African. SAT 1 diverged first 397 years ago, followed by sequential divergence of serotype SAT 2 (396 years ago), A (147 years ago), O (121 years ago), Asia 1 (89 years ago), C (86 years ago), and SAT 3 (83 years ago). Bayesian skyline plot reveals a population expansion in the early 20th century that is followed by a rapid decline in population size from the late 20th century to the present day. Within each serotype, there was no apparent periodic, geographic, or host species influence on the evolution of global FMD viruses. At least seven genotypes of serotype Asia 1 are known.[23]
Transmission[edit]
The FMD virus can be transmitted in a number of ways, including close-contact, animal-to-animal spread, long-distance aerosol spread and fomites, or inanimate objects, typically fodder and motor vehicles. The clothes and skin of animal handlers such as farmers, standing water, and uncooked food scraps and feed supplements containing infected animal products can harbor the virus, as well. Cows can also catch FMD from the semen of infected bulls. Control measures include quarantine and destruction of both infected and healthy (uninfected) livestock, and export bans for meat and other animal products to countries not infected with the disease.
There is significant variation in both susceptibility to infection and ability to spread disease between different species, virus strains, and transmission routes. For example, cattle are far more vulnerable than pigs to infection with aerosolized virus, and infected pigs produce 30 times the amount of aerosolized virus compared to infected cattle and sheep.[24][25] Also, pigs are particularly vulnerable to infection through the oral route.[26] It has been demonstrated experimentally that FMD can be spread to pigs when they eat commercial feed products contaminated by the FMD virus. Also, the virus can remain active for extended periods of time in certain feed ingredients, especially soybean meal. Feed biosecurity practices have become an important area of study since a 2013 outbreak of Porcine Epidemic Diarrhea Virus (PEDV) in the US, thought to be introduced through contaminated feed. [27]
Just as humans may spread the disease by carrying the virus on their clothes and bodies, animals that are not susceptible to the disease may still aid in spreading it. This was the case in Canada in 1952, when an outbreak flared up again after dogs had carried off bones from dead animals.[3] Wolves are thought to play a similar role in the former Soviet Union.[28]
Daniel Rossouw Kannemeyer (1843–1925) published a note in the Transactions of the South African Philosophical Society volume 8 part 1 in which he links saliva-covered locusts with the spread of the disease.[29]
Transmission of the FMD virus is possible before an animal has apparent signs of disease, a factor that increases the risk that significant spread of the virus has occurred before an outbreak is detected. A 2011 experiment measured transmission timing in cattle infected with serotype O virus by exposing susceptible cattle in 24-hour increments. It estimated the infectious period of the infected cattle to be 1.7 days, but showed the cattle were only infectious for a few hours before they developed fevers or classic FMD lesions. The authors also showed that the infectious period would have been estimated to be much higher (4.2 to 8.2 days) if detection of virus had been used as a substitute for infectiousness.[30] A similar 2016 experiment using serotype A virus exposed susceptible pigs to infected pigs for 8 hour periods and found that pigs were able to spread disease for a full day before developing signs of disease.[31] Analysis of this experimental data estimated the infectious period to be approximately 7 days.[32] Again, the study showed that detection of virus was not an accurate substitution for infectiousness. An accurate understanding of the parameters of infectiousness is an important component of building epidemiological models which inform disease control strategies and policies.
Infecting humans[edit]
Humans can be infected with FMD through contact with infected animals, but this is extremely rare.[33] Some cases were caused by laboratory accidents. Because the virus that causes FMD is sensitive to stomach acid, it cannot spread to humans via consumption of infected meat, except in the mouth before the meat is swallowed. In the UK, the last confirmed human case occurred in 1966,[34][35] and only a few other cases have been recorded in countries of continental Europe, Africa, and South America. Symptoms of FMD in humans include malaise, fever, vomiting, red ulcerative lesions (surface-eroding damaged spots) of the oral tissues, and sometimes vesicular lesions (small blisters) of the skin. According to a newspaper report, FMD killed two children in England in 1884, supposedly due to infected milk.[36]
Another viral disease with similar symptoms, hand, foot and mouth disease, occurs more frequently in humans, especially in young children; the cause, Coxsackie A virus, is different from the FMD virus. Coxsackie viruses belong to the Enteroviruses within the Picornaviridae.
Because FMD rarely infects humans, but spreads rapidly among animals, it is a much greater threat to the agriculture industry than to human health. Farmers around the world can lose enormous amounts of money during a foot-and-mouth epizootic, when large numbers of animals are destroyed, and revenues from milk and meat production go down.
United States 1870–1929[edit]
The US has had nine FMD outbreaks since it was first recognized on the northeastern coast in 1870;[39] the most devastating happened in 1914. It originated from Michigan, but its entry into the stockyards in Chicago turned it into an epizootic. About 3,500 livestock herds were infected across the US, totaling over 170,000 cattle, sheep, and swine. The eradication came at a cost of US$4.5 million (equivalent to $116 million in 2020).
A 1924 outbreak in California resulted not only in the slaughter of 109,000 farm animals, but also 22,000 deer.
The US had its latest FMD outbreak in Montebello, California, in 1929. This outbreak originated in hogs that had eaten infected meat scraps from a tourist steamship that had stocked meat in Argentina. Over 3,600 animals were slaughtered and the disease was contained in less than a month.[40][41]
See also[edit]
- Animal virology
- Hand, foot and mouth disease (HFMD)
- Swine vesicular disease (SVD)
- Blain, an archaic disease of uncertain etiology
https://en.wikipedia.org/wiki/Foot-and-mouth_disease
hand food mouth disease dematological condition skin integument relate to virus-etc.
vesicular disease; myxoma
myocarditis porcine
pox virus blue tongue
pustules (pox-mollusk-etc.), bubules (hep-her), equine sarcoid
cond or circu of infectious agent effect cancer
Bluetongue disease is a noncontagious, insect-borne, viral disease of ruminants, mainly sheep and less frequently cattle,[1]yaks,[2] goats, buffalo, deer, dromedaries, and antelope. It is caused by Bluetongue virus (BTV). The virus is transmitted by the midges Culicoides imicola, Culicoides variipennis, and other culicoids.
https://en.wikipedia.org/wiki/Bluetongue_disease
A myxoma (New Latin from Greek 'muxa' for mucus) is a myxoid tumor of primitive connective tissue.[1] It is most commonly found in the heart (and is the most common primary tumor of the heart in adults) but can also occur in other locations.
https://en.wikipedia.org/wiki/Myxoma
above.
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