Ruptured blisters on the feet of a pig The incubation period for<unk>  virus has a range between one and 12 days. The disease is characterized by high fever that declines rapidly after two to three days, blisters inside the<unk>  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<unk> s, as well as swelling in the testicles of mature males, and cows' milk production can decline significantly. Though most animals eventually recover from<unk> , 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 the virus and may be able to transmit it to others. Pigs cannot serve as asymptomatic carriers. Subclinical Infection 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<unk>  virus (about 1 to 2 days) and last about 8 to 14 days. 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<unk>  virus to other animals. Neoteric subclinical infections often occur in vaccinated animals but can occur in unvaccinated animals as well. 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. Animals can become carriers following acute infections with or without symptoms. Both vaccinated and unvaccinated animals can become carriers. Transmission of the<unk>  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<unk>  and on the feet. This supports the theory that while the likelihood of a carrier spreading<unk>  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<unk> -freedom is longer when vaccination rather than slaughter is used as an outbreak-control strategy. As a result, many<unk> -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<unk> -free status. Although the risk of transmission from an individual<unk>  carrier is considered to be very low, there are many carriers in<unk> -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<unk>  virus. This fact complicates disease control, as the two types of subclinical infections have significantly different risks of spreading disease.
Foot-and-mouth disease
Tongue disease
Plague 
Chickenpox
Polymeal
Sealpox
Shingles
Mumps