Genetic Determinants of Altered Virulence of Taiwanese Foot-and-Mouth Disease Virus

In 1997, a devastating outbreak of foot-and-mouth disease (FMD) in Taiwan was caused by a serotype O virus (referred to here as OTai) with atypical virulence. It produced high morbidity and mortality in swine but did not affect cattle. We have defined the genetic basis of the species specificity of OTai by evaluating the properties of genetically engineered chimeric viruses created from OTai and a bovine-virulent FMD virus. These studies have shown that an altered nonstructural protein, 3A, is a primary determinant of restricted growth on bovine cells in vitro and significantly contributes to bovine attenuation of OTai in vivo.