Porcine reproductive and respiratory syndrome viruses (porcine arteriviruses)

Control of porcine reproductive and respiratory syndrome virus (PRRSV) remains problematic, and economic studies have uniformly shown that PRRSV inflicts major losses on swine health and productivity. A fuller picture of PRRSV genetic relationships and evolutionary origins may be facilitated by whole genome analyses and comparisons of multiple protein coding regions, including the polymerase gene, which is widely used in RNA viral evolutionary analyses. PRRSV viral infection can be divided into three distinct stages: acute infection, persistence, and extinction. Acute infection follows exposure and is characterized by rapid spread to primary sites of replication in lung and lymphoid tissues. PRRSV markedly alters innate immunity and inflammatory and immunoregulatory cytokines in a strain- specific manner. Infection with PRRSV induces immunity that eventually controls the initial infection, eliminates the virus, and establishes memory that is variably protective against future infection.