Foot-and-mouth disease

Foot-and-mouth disease (FMD) or hoof-and-mouth disease (HMD) is an infectious and sometimes fatal viral disease that affects cloven-hoofed animals, including domestic and wild bovids. The virus causes a high fever for between two and six days, followed by blisters inside the mouth and on the feet that may rupture and cause lameness. Foot-and-mouth disease (FMD) or hoof-and-mouth disease (HMD) is an infectious and sometimes fatal viral disease that affects cloven-hoofed animals, including domestic and wild bovids. The virus causes a high fever for between two and six days, followed by blisters inside the mouth and on the feet that may rupture and cause lameness. Foot-and-mouth disease (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, feed, and by domestic and wild predators. Its containment demands considerable efforts in vaccination, strict monitoring, trade restrictions, quarantines, and occasionally the culling of animals. Susceptible animals include cattle, water buffalo, sheep, goats, pigs, antelope, deer, and bison. It has also been known to infect hedgehogs and elephants; 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. In laboratory experiments, mice, rats, and chickens have been artificially infected, but they are not believed to contract the disease under natural conditions. Humans are rarely infected. The virus responsible for the disease is a picornavirus, 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, which limits the effectiveness of vaccination. The incubation period for foot-and-mouth disease virus has a range between one and 12 days. The disease is characterized by high fever that declines rapidly after two or 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. 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) and death, especially in newborn animals. Some infected ruminants remain asymptomatic carriers, but they nonetheless carry FMDV and may be able to transmit it to others. Pigs cannot serve as asymptomatic carriers. Of the seven serotypes of this virus, A, C, O, Asia 1, and SAT3 appear to be distinct lineages; SAT 1 and SAT 2 are unresolved clades. 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 FMDVs. At least seven genotypes of serotype Asia 1 are known. 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 infected livestock, and export bans for meat and other animal products to countries not infected with the disease. 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. Wolves are thought to play a similar role in the former Soviet Union. 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.