Editorial on the Research TopicPorcine reproductive and respiratory syndrome virus -animal virology, immunology, and pathogenesis Porcine reproductive and respiratory syndrome (PRRS) is one of the most important pig diseases causing huge economic losses worldwide. The causative agent, PRRS virus (PRRSV), is an enveloped, single-stranded, positive-sense RNA virus which is classified into the genus Betaarterivirus, subfamily Variarterivirinae, family Arteriviridae along with equine arteritis virus (EAV), lactate dehydrogenase-elevating virus of mice (LDV), and simian hemorrhagic fever virus (SHFV). Its genome is about 15 kb in length and contains at least 11 open reading frames (ORFs) with 5´cap and 3´polyadenylated tail (1-3). The nonstructural proteins (nsp1-12), owning the functions of protease, replicase and regulation of host cell gene expression and responsible for the synthesis of viral RNA, are encoded by ORF1a and ORF1b which occupy approximately two-thirds of the genome (4). The structural proteins including glycoprotein 2 (GP2), GP3, GP4, GP5, envelope protein (E), matrix protein (M), and nucleocapsid protein (N), expressed by a series of subgenomic RNAs, are encoded by ORFs 2-7 at the 3´terminus of the genome (5). Due to the lack of proofreading ability of PRRSV RNA-dependent RNA polymerase (RdRp), the viral genome is highly susceptible to mutation and recombination, which causes the emergence of novel PRRSV isolates worldwide (6). At present, PRRSV can be divided into two species: PRRSV-1 (European genotype, Betaarterivirus suid 1) and PRRSV-2 (North American genotype; Betaarterivirus suid 2). Both species show high genetic diversity and share approximately 60% nucleotide sequence identity, and each one can be further divided into several clades, substrains or lineages. In China, the dominant strains are PRRSV-2 and the outbreaks of highly pathogenic variants lead to concerns in the pig industry (7). PRRSV infection causes severe reproductive failure in sows and respiratory disease in pigs of all ages, which often leads to secondary bacterial infections (such as Haemophilus parasuis and Streptococcus suis) with greater clinical manifestations and higher mortality (8).