 BVDV-1 isolates have been grouped into 16 subtypes (a –p) and BVDV-2 has currently been grouped into 3 subtypes (a – c).BVDV strains can be further divided into distinct biotypes (cytopathic or non-cytopathic) according to their effects on tissue cell culture; cytopathic (cp) biotypes, formed via mutation of non-cytopathic (ncp) biotypes, induce apoptosis in cultured cells.Ncp viruses can induce persistent infection in cells and have an intact NS2/3 protein.