The viral particle, or virion, contains a single-stranded RNA of positive polarity, approximately 8500 nucleotides long. It is an icosahedral particle with a smooth surface and a diameter of about 30 nm [13] . The fine structure of the virus has been described by X-ray crystallography [16, 41, 42] . There are 60 copies of each of the structural protein VP1, VP2, VP3, and VP4. While the first three structural proteins (MW≈24 kDa) have surface components, the fourth (MW≈8.5 kDa) is internal. The virion is also usually composed of one or two units of VP0, the precursor of VP2 and VP4 [16, 43] . The structural proteins, VP1-3 fold into an eight-stranded wedge-shaped 13-barrel which fits together to form the majority of the capsid structure [16] . The three-dimensional structure of FMDV has revealed a prominent surface feature formed by the loop between the G and H strands of VP1. The VP4 protein is located inside the capsid [44] . The strands of the 13-barrel of VP1-3 are connected by loops which form the outer surface of the virion [45] . Unlike other picornaviruses, FMDV lacks a surface canyon or pit which is the receptor binding site for entero-and cardioviruses [46] . Another feature of the virion is the channel at the fivefold axis which permits the entry of small molecules such as Cscl into the capsid resulting in FMDV having the highest buoyant density of the picornaviruses [42] .