Preliminary Study on Prevalence, Risk Factor and Genetic Homogeneity of Porcine Reproductive and Respiratory Syndrome Virus in Registered Pig Farms in Heilongjiang, China.

While porcine reproductive and respiratory syndrome (PRRS) causes great economic losses in southern and central China, systematic studies on the epidemiology of PRRS virus (PRRSV) in Heilongjiang Province had not been performed. Therefore, we conducted a preliminary study to estimate the prevalence and risk factors associated with PRRSV infection, as well as characterize the PRRSV in registered pig farms in Heilongjiang Province, China in 2011. A total of 1237 blood samples were collected from 72 farms and tested by reverse transcription polymerase chain reaction (RT-PCR) for PRRSV. Risk factors associated to PRRSV infection were analysed using logistic regression models. Genes of non-structural protein-2 (Nsp2) and glycoprotein 5 (GP5) from 22 isolates were sequenced for phylogenetic analysis. The results showed that the herd apparent prevalence was 9.7% (95% CI: 6.3, 13.1) in Heilongjiang Province. An increased risk of PRRSV infection on farms was associated with unrestricted movement of external people (OR = 14.1, 95% CI: 1.68, 119.07), close proximity (<1 km) to the nearest house, road or neighbouring farm (OR = 16.2, 95% CI: 1.52, 171.80), and selling farm products at both local and provincial markets (OR = 20.6, 95% CI: 2.02, 210.56). Phylogenetic analysis based on partial amino acid sequences of GP5 and Nsp2 showed that all the 22 PRRSV isolates in Heilongjiang are closely related to the highly pathogenic PRRSV strain JXA1 and belong to the Genotype 2 (American genotype). The prevalence, determination of risk factors and phylogenetic characterization will provide information for future epidemiological studies and a reference for developing surveillance and control strategies in this region.