This document discusses the etiology, pathogenesis, and epidemiology of porcine reproductive and respiratory syndrome (PRRS) in the Asia Pacific region. PRRS is caused by the PRRS virus (PRRSV), which is an enveloped, single-stranded RNA virus. There are two major genotypes of PRRSV, type 1 (European) and type 2 (North American), which share about 60% genetic identity. In 2006, a highly virulent strain of PRRSV emerged in China that caused high fever and high mortality in pigs. Known as highly pathogenic PRRS (HP-PRRS), this strain is characterized by a 30 amino acid deletion in its nsp2 region. Since 2007,