Healthy and infected cows. Thermogram (infrared) images of a cow infected with the foot-and-mouth-disease virus (left) and a healthy cow (right). The effects of the disease cause the hooves to be hotter than usual, showing up on the thermogram as a red colour at left. For the uninfected cow at right, no heat or red colour is seen in the hooves. Foot-and-mouth disease is caused by viruses in the picornavirus group. It is highly contagious, spreading by direct contact with infected animals. Infected farm animals are slaughtered and burnt to remove contamination.