Porcine Reproductive and Respiratory Syndrome (PRRS) virus is one of the most important pathogens the swine industry is currently dealing with. The impact of the virus is not only caused by the disease itself, but is also due to increased prevalence of secondary infections. On “problem” farms, where farm management and biosecurity measures cannot fully control the disease, an immunomodulation strategy could help control PRRS.
PRRS virus (PRRSV) belongs to the family of arterivirus_es and is a small, enveloped, positive single-stranded RNA virus. Clinical signs of PRRS are highly variable. Substantial increases in abortions, stillbirths, pre-weaning mortality and respiratory diseases in weaners and growers are commonly reported clinical signs of PRRS. The susceptibility of PRRSV-infected pigs to secondary bacte_rial or viral infections increases dramatically. For instance, concurrent infections with Streptococcus suis are frequently reported. The prevalence of secondary infections together with the direct losses caused by PRRSv are the reason for the major economic impact of this viral syndrome. One of the main target cells for PRRSV replication are porcine alveolar macrophages (PAMs). These cells serve as the first line of defence against inhaled microbial particles by means of phagocytosis, antigen presentation and production of cytokines. These basic functions are directly impaired when PRRSV replicates in PAMs.