Porcine reproductive and respiratory syndrome virus (PRRSV): Immunization strategies, virulence of various isolates, and efficacy of DNA vaccination

This review is intended to discuss published work focused on the immunization of swine against porcine reproductive and respiratory syndrome virus (PRRSV). Many different strategies have been pursued by researchers in the quest for control and ultimately the eradication of porcine reproductive and respiratory syndrome (PRRS). Some of the strategies have lead to the licensure of commercial products while others have provided insight into the biology of PRRSV. Many of the strategies examined here have contributed to the overall understanding of the host’s immune response to PRRSV. Some strategies have provided unconventional or in some cases controversial methods of protecting swine from PRRS. The main area of interest in this review will be the clinical protection of swine from virulent PRRSV challenge. Gross lung pathology and viremia along with virus neutralizing antibody titers will serve as the primary parameters for protection in the respiratory challenge model, whereas the number of live born pigs and the number of weaned pigs along with piglet viremia will serve as the primary parameters for protection in the reproductive challenge model. Despite the incomplete reporting of these primary parameters, some publications will be discussed that have focused on protection against PRRSV by either evaluating the immune responses in non-target animals or studies conducted in swine, some without a virulent challenge. It is important to note that for the purposes of this review a homologous PRRSV challenge will be defined as a challenge with the same viral isolate from which the