Foot-and-mouth disease virus surface protein, molecular model. Foot-and-mouth disease (FMD) affects cloven-hooved mammals, commonly cattle and pigs. Infected animals suffer fever, blistering on the hooves and mouth, and sometimes death. It is caused by an Aphthovirus, which has a protein structure (capsid, shown here) surrounding its genetic material. The capsid protein has four domains, shown in orange, red, green and blue in this model. The solid colours represent the secondary structure of the protein (spiral ribbons are alpha helices; arrows are beta sheets), and the faded tubular structure behind represents the individual atoms and bonds.