Foot-and-mouth disease virus. Molecular model of the foot-and-mouth disease (FMD) virus Aphtae epizooticae, with antibodies (immunoglobulins, yellow) attached to the virus's outer protein coat (capsid). FMD affects cloven-hooved mammals, commonly cattle and pigs, and is highly contagious. Antibodies are created by an animal's immune system to identify and neutralize foreign objects (antigens), such as bacteria and viruses. Each antibody is specific to a particular antigen. A specialised region (hypervariable region) on the antibody binds to a specific site on the antigen's surface, rendering it ineffective.