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 the virus 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 FMD viruses. 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 both infected and healthy (uninfected) 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.