Epidemiological Investigation And Pathogenic Analysis Of Porcine Viral Diarrhea Part Area Of Shaanxi Province

PEDV and TGEV are the main pathogens of porcine viral diarrhea susceptible to pigs of all ages(especially the sucking piglets).Diarrhea,dehydration and vomiting are the main clinical features after animal infection.PEDV and TGEV have become one of the important reasons to reduce the survival rate of sucking piglets and lead to huge economic losses to pig industry of all over the world.In order to understand the epidemiological and etiology characteristics of PEDV and TGEV in Shaanxi Province,clear the genetic relationship and variation of the vaccine strain,classical strain,popular strain with Shaanxi popular strain,so as to provide theoretical basis and reference data for comprehensive prevention and control of PEDV and TGEV,and develop more rational and effective vaccines.This study investigated epidemiological investigation of PEDV and TGEV of Shaanxi Province,and analyzed the genetic variation of this two virus.The results were as follows:1.714 diarrhea samples were detected of PEDV by PCR.The results showed PEDV positive samples were detected in 288 cases,the positive rate of PEDV was 40.33%.PEDV was detected in Xi’an,Xianyang,Weinan and Baoji,while the highest positive rate of PEDV in Xi’an was 46.94%.PEDV was detected in each season,and the highest positive rate of PEDV in winter was 57.96%.PEDV was also detected in all pigs at different growth stages,and the highest positive rate of PEDV in sucking piglets was 70.42%.2.714 diarrhea samples were detected of TGEV by PCR.The results showed TGEV positive samples were detected in 69 cases,the positive rate of TGEV was 9.97%.Mixed infection of PEDV and TGEV positive samples were detected in 20 cases,the positive rate was 2.81%.TGEV was detected in Xi’an,Xianyang,Weinan and Baoji,and highest positive rate of TGEV in Xianyang was 14.34%.TGEV was detected in each season,and the highest positive rate of TGEV in winter was 17.05%.TGEV was detected in suckling piglets,weanling piglets,finishing pigs and multiparous pigs,the positive rate of TGEV were 15.88%,8.52%,4.45%,7.29%,respectively,while the replacement sows and breeding boars not detected the TGEV.3.The virus was isolated by inoculating Vero cells with the treated PEDV positive samples.The virus was identified by cytopathic observation,PCR and electron microscopy.The results showed that the virus could make the cells become rounded,shrinking,and then the cells were disrupted,shedding and drawing.The PCR and electron microscopy also proved the isolation was PEDV,named PEDV-SX.The genome sequence of vaccine strain CV777 was used as template and Primer 5.0 was used to design 15 pairs of overlapping primers for whole genome amplification and sequencing.The sequences were mosaified by SeqMan software in DNA star software,and homologous comparison and genetic evolution analysis of the target gene were performed by MegAlign software.The results showed that the homology between the PEDV-SX strain and vaccine strains were 98%,the classical strains were 97.8%,the epidemic strains at home and abroad were 97.2% ~ 99.9%.PEDV-SX strain,SD-M strain and JS2008 strain were on the same branch of phylogenetic tree.4.The sequence of TGEV S,M,N and E gene were obtained by molecular cloning.The target gene homology and genetic evolution were analyzed by MegAlign software in DNA star software.The results showed that the homology of S,M,N and E gene of TGEV-SX strain with the 8 reference strains were 98.0% ~ 99.5%,98.1% ~ 100%,97.9% ~ 99.8% and 96.8% ~ 99.2%,respectively.The S gene of TGEV-SX strain,SC-Y strain,SHXB strain,Purdue virulent,Purdue P115 strain belong to a same branch of phylogenetic tree.While M,N and E gene of TGEV-SX strains on a same branch of phylogenetic tree with Miller M6 strain,M60 strain,H16 strain and TS strain,respectively.This study found that both PEDV and TGEV occurred in part area of Shaanxi province and had mixed infection,but the infection rate of PEDV was higher,and it was mainly infected the suckling piglets.Homologous comparison and genetic evolution analysis showed that the PEDV-SX strain was close to the SD-M strain and the JS2008 strain while far from the vaccine strain CV777.We also found that the TGEV-SX strain S gene,SC-Y strain,SHXB strain,Purdue virulent,Purdue P115 strain had close relationship,while TGEV-SX strains M,N,E gene and H16 strain,TS strain,Miller strains had close relationship.