Vaccination is the principal means used to control and treat porcine reproductive and respiratory syndrome virus (PRRSV) infection. An array of PRRS vaccine products is available in various regions of the world. However, despite extensive efforts, little progress has been made to improve efficacy since the first introduction of a live, attenuated vaccine in 1994 in the USA. Key limitations include: (a) uncertainty about the viral targets of protective immunity that prevents a research focus on individual viral structures and proteins, and frustrates efforts to design novel vaccines; (b) inability to establish clear immunological correlates of protection that requires laborious in vivo challenge models for evaluation of protection against challenge; and (c) the great genetic diversity of PRRSV which requires that challenge experiments be interpreted cautiously since it is not possible to predict how immunological protection against one isolate will translate to broadly cross-protective immunity. Economically significant levels of cross-protection that are provided to a variety of field isolates still cannot assure that effective protection will be conferred to isolates that might emerge in the future. In addition to these substantial barriers to new PRRSV vaccine development, there are enormous gaps in our understanding of porcine immunological mechanisms and processes that provide immunity to PRRSV infection and memory responses for long-term protection. Despite these impediments, we should be confident that progress will be made. Sequencing of the swine genome is providing a rich source of primary knowledge of gene structure and transcriptional regulation that is certain to reveal important insights about the mechanisms of anti-PRRSV immunity, and continued efforts to unravel the details of the interaction of PRRSV with pigs will lead to new insights that overcome the current limitations in the field.
- Animal virus