The virus is easily transmitted by physical contact with other animals, people, or materials. Nearly 100 percent of exposed, susceptible animals will become infected. The virus can become airborne, traveling many miles in the wind. Animals are infected through inhalation or ingestion of the virus. The incubation period for swine and cattle is two to seven days, and 14 days for sheep.
Temperatures rise markedly, and then usually fall in about two to three days.
The disease is fatal for 2-10 percent of adult animals and up to 20 percent of young animals. All affected animals lose condition and secondary bacterial infections may prolong convalescence. The most serious effects of the disease, however, are in dairy cattle. Loss of milk yield, abortion, sterility, chronic mastitis, and chronic lameness are commonplace. Bovine spongiform encephalopathy, sometimes called mad cow disease, is a slowly progressing, degenerative disease affecting the central nervous system of cattle.