Foot-and-mouth-disease cow. Thermogram (infrared) image of a cow infected with the foot-and-mouth-disease virus. The effects of the disease cause the hooves to be hotter than usual, showing up on the thermogram as a red colour. 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.