Epidemiological Investigation Of Porcine Pseudorabies In Shandong Province

Porcine pseudorabies(PR),caused by Pseudorabies virus(PRV),is an acute contact dermatitis and zoonotic infectious disease mainly manifested with fervescence,neurological sign,a series of reproductive failure like pruritus,decreasing returning rate,infertility,foetal mummification,abortion and stillbirth,and neurological sign and diarrhea of newborn piglet.In addition,PRV usually co-infected with other virus,bacteria and parasites,which would affect the diagnosis and disease control of PRV,bring great economic loss to swine industry in our country,and pose a threat to swine industry.Vaccination is the major measure of PR prevention and control.Since 1990s,PRV attenuated vaccines were widely used in large-scale pig farms in China,and outbreaks of PR had been generally contolled.However,PRV infection is prevalent again in constant increasing pig farms in eartheast,northeast,and southeast of China since 2012.What is very worrying is that pigs vaccinated with attenuated vaccines even been infected with varinant PRV.To gain a more comprehensive konwlegde of PRV wild virus infection and PR epidemic status in Shandong Province,large-scale pig farms located in Zibo,Yucheng,Weifang,Jiyang,Jinan,Changle,and Tai’an in Shandong province which had been infected with PRV were selected as the object of study.438 clinical samples suspected to be infected with PRV and 1482 serum samples form 2014 to 2015 were collected.Then,PR epidemic status in Shandong Province was investigated from two aspects of molecular epidemiological investigation and surem investigation,which would provide scientific evidence of PRV prevention and control.Firstly,PCR method for PRV detection was established.For this method,PRV gE gene with a fragment of 406bp could be amplified in PRV DNA samples specificly.Then,PRV molecular epidemiological investigation was conducted using this method.The results showed that,the total positive rates of PRV infection in Shandong province was 46.80%,while the positive rates were abnormal higher in some regions like Yucheng and Weifang,which implied that PRV infection were widely exsisted in Shandong Province.To further confirm this result,four PCR products selected randomly from positive samples in Weifang,Yucheng,Zibo and Jinan were purified and cloned into vectors.Sequence analysis illustrated that,the homology of PRV gE gene between four strains isolated from Shandong Province and other strains in Genebank was among 96%and 100%.Furthermore,the phylogenetic tree demonstrated that all the four viral strains were located at the same clade,implying that they may have the relatively close phylogenetic relationship.Afterwards,PRV gE and gB antibody titers were measured in pig serums using IDEXX ELISA kits.As we kown,the gE antibody titer could used as an index indicating the PRV wild strain infection.The results showed that,the total positive rate of PRV gE in Shandong Province was 33.67%,while positive rates in every regions were ranged from 6.45%to 63.29%,indicating that PRV wild strain infection was exsisted in farm in Shandong.On the other hand,the positive rates of PRV gB antibody were 100%in all regions,indicating an ideal immunization coverage of PRV vaccines.Combined with the results of molecular epidemiological investigation and surem investigation,it could be concluded that the positive rate of PRV was raletively higher in Shandong Province,especially in some specific regions.More attention of farms and Veterinary Authorities were needed in the PR prevention and control.