Animals pick up the disease through direct contact with the virus. Infection usually begins and builds up in the respiratory tract. Infected animals breathe out large volumes of the virus in aerosol form, and milk, feces, semen, saliva and urine contain the virus. In aerosol form the disease can spread a considerable distance through air and wind, especially when humidity is above 60 percent. Haskell says milk tankers can spread the disease from farm to farm, and feeding infected meat meal is a common source of contamination.
Pigs eating infected feed can easily spread the disease to cattle.
However, mechanical spread of the disease by birds is considered unlikely. The disease can survive in dry fecal material for 14 days in summer, in slurry for six months in winter, in urine for 39 days and on the soil for up to 28 days. When an animal is newly infected, there is an incubation period of 2-14 days before symptoms show up. After the incubation period, a fever of 106 degrees develops. The animal goes off feed and salivates, and blisters form on the mouth, teats and feet.