Origination and consequences of bovine viral diarrhea virus diversity

The purpose of this article is to provide an overview of genetic, antigenic, and biologic diversity among bovine viral diarrhea viruses (BVDV), and to discuss the impact of that diversity on disease manifestations, diagnostic testing, and disease control strategies. The genetic diversity that occurs among isolates of BVDV is characteristic of RNA viruses that exist in nature as quasispecies (a swarm of viral mutants). The basis for the viral quasispecies phenomenon will be discussed briefly and related to recent evidence for the existence of BVDV Lis a quasispecies. The genetic diversity that occurs among BVDV is reflected in the antigenic diversity found among viral isolates worldwide. The persistently infected (PI) animal is considered important for maintaining BVDV in nature, and as being a primary source of virus for other cattle. PI cattle may also serves as a source of viral genetic variants that may be "selected" by non-PI cattle when infected with virus. The emergence and establishment of genetic and antigenic variants of BVDV also is affected by selective pressure applied to the virus by the innate and adaptive host immune responses. The array of disease manifestations seen during infection with BVDV, and the corresponding pathogenic processes, may be attributed to viral diversity; however, the definitive viral markers for tissue tropism Or Virulence have yet to be identified.