Porcine reproductive and respiratory syndrome virus (PRRSV) is the most costly viral pathogen facing a modern pig industry. A unique feature of the virus is the ability to cause severe clinical disease and maintain a life-long subclinical infection. Persistence at the population level poses the biggest challenge for the successful control and elimination of the disease. A mechanistic basis for persistence includes the evasion of innate and adaptive immune responses. Recent advances include the study of how the non-structural proteins (nsp's) inhibit the induction of type 1 interferon genes.