A Pilot Investigation Of Porcine Reproductive And Respiratory Syndrome In Heilongjiang Province

Porcine reproductive and respiratory syndrome (PRRS)， caused by porcine reproductive andrespiratory syndrome virus (PRRSV), is one of the most important viral diseases in pig and hascaused great economic losses in many provinces，China. However, the PRRS status in Heilongjiangis unclear to date. Therefore, we conducted a pilot investigation to estimate the prevalence of,identify potential risk factors associated with, and analyze the phylogenetic evolution of PRRSV inHeilongjiang province.Blood samples were collected from653piglets and584sows,524of which from immunizedpigs, while the others from non-immunized pigs. PRRSV serum antibodies and gene of Nsp2weredetected using ELISA and RT-PCR method, respectively. The relationship between potential riskfactors and PRRSV infection in farms was analyzed using a regression model. Animo acidsequences of Nap2and GP5protein from the new isolates in Heilongjiang were analyzed to infertheir phylogenetic evolution using Neighbor-joining method and bootstrap test.The ELISA test results show that the PRRSV antibody positive proportion in immunizedpiglets and sows were61.5%(95%CI:58.6,64.4) and81.7%(95%CI:79.3,84.1), respectively.While in non-immunized pigs, the sero-prevalence in piglets, sows and herds were52.3%(95%CI:49.8,54.8),63.6%(95%CI:61.0,66.2) and92.9%（95%CI:89.0，96.8）, respectively. The PCRtest results show that seven of72farms had at least one positive pig. The apparent prevalence was9.7%(95%CI:3.6,13.1) in farm. The prevalence of PRRSV in piglets and sows were2.9%(95%CI:2.3,3.5) and0.5%(95%CI:0.2,0.8), respectively. The prevalence of PRRSV in pigletswas significant higher(p<0.05) than in sows. Regression model analysis results indicate that anincreased risk of PRRSV infection in farms in Heilongjiang province was associated withunrestricted proximity people(OR=14.1295%CI：1.7,119.1P=0.015), less than1km of thedistances between the nearest farm, human house, or road1km(OR=16.1595%CI：1.5,171.8P=0.021) and selling of the farm products at both local and other province’s market (OR=20.6495%CI：2.0,210.6P=0.011). The evolutionary trees of both Nsp2a and GP5indicate that thePRRSV isolates in Heilongjiang were closely related to recent isolates in China, which belonged tothe North American genotype.The results show the evidence of the presence of PRRSV in Heilongjiang province. Prevalence, risk factors and phylogenetic characters obtained in this study provide basic information for thecontrol and further investigation of PRRSV in Heilongjiang province.