Bovine Viral Diarrhea Virus

Bovine viral diarrhea (BVD) is prevalent worldwide and causes high economic losses in cattle due to a variety of disease syndromes. BVD is caused by three bovine pestiviruses, bovine viral diarrhea virus 1 (BVDV-1), BVDV-2 and HoBi-like pestivirus (HoBiPeV) with considerable genetic and antigenic heterogeneity. Bovine pestiviruses belong to the Pestivirus genus within the Flaviviridae family that also comprises the genera Flavivirus, Hepacivirus and Pegivirus. As per the latest (10th) ICTV report, pestiviruses have been classified into 11 approved species, including bovine pestiviruses, which have been classified into species, Pestivirus A, Pestivirus B and Pestivirus H. The term BVDV in this chapter commonly refers to all the three bovine pestiviruses. The pathogenesis of BVDV infection is complex, with infection pre- and post-gestation leading to different outcomes. BVDVs are highly successful to persist and spread in their host populations due to their unique ability to produce persistent infection through evasion of adaptive immune response and innate immune response. Recent advances in diagnostic methods, nucleotide sequencing, and computer-assisted phylogenetic analyses have so far identified 21 BVDV-1 subtypes (BVDV-1a to BVDV-1u), 4 BVDV-2 subtypes (BVDV-2a to BVDV-2d) and 4 HoBiPeV subtypes (HoBiPeV-a to HoBiPeV-d). Providing acquired immune protection against BVDV is challenging due to the antigenic diversity among BVDV strains and ability of BVDV to infect the fetus. Both killed and live attenuated vaccines have been reported to be effective in the field, and recent advancements in molecular studies have helped toward future development of new-generation vaccines against BVD. However, over the years, vaccination alone has not resulted in the elimination of BVDV-related clinical disease or a significant reduction in BVDV losses. All successful BVDV control programs are based on identification and removal of PI animals, movement controls, strict biosecurity and surveillance. To date, BVDV control programs without vaccination have been implemented successfully in Scandinavian countries, Austria and Switzerland, while control with vaccination has been used in Germany, Belgium, Ireland and Scotland. This chapter will focus on advances in research involving all aspects of BVDV with special emphasis on molecular biology, genetic and antigenic diversity, diagnosis, prevention and control besides discussion on future perspectives.