| Pseudorabies was an acute infectious disease caused by pseudorabies virus.Pseudorabies virus(PRV)infection in domestic pigs may cause lethality or acute infectious diseases that affect pig growth and reproduction,and has a great impact on pig industry.Although the pseudorabies vaccine in swine was effective to control pseudorabies,it keeps occurring in pig farms in China.Therefore,this study investigated the epidemic law of PRV in an large-scale pig farm,which suffer heavy economic losses..to develop the comprehensive prevention and control measures in PRV in this pig farm through epidemiological investigation,laboratory test,improving the biosafety system and adjusting the immunization program.1.Epidemiological investigation 1.Epidemiological investigation In this study,the statistical analysis were performed about the incidence of this pig farm and the multiple pathogen detections on the affected pigs were carried out.The respiratory symptoms were shown in fattening pigs firstly,and then the pregnant sows abortion and d piglets death appeared.Then,The pseudorabies virus infection was determined according to the clinical characteristics and the results of autopsy.In order to understand the distribution and the transmission law of pseudorabies virus(PRV)in the farm comprehensively,the fluorescence quantitative detection was constructed(including the sampling of pig herd,barn,environment,feed,water and feces).The results showed that the highest amount of virus was found in fattening pigs,mainly concentrated in 60-100 days old(33.3%,10/30),and the positive detection rate gradually decreased with the increase of age.The positive detection rate of PRV pathogens was 10.3%(3/29)at 100-150 days old,and 5.7%(2 / 35)at 150-210 days old.The positive detection rate of PRV pathogen increased gradually from weaning(15.6%,5/32),pre-pregnancy(19.5%,7/36)to mid pregnancy(22.5%,7/31),respectively.From late pregnancy to lactation,the positive detection rate of PRV showed a decreasing trend,which were 17.2%(5/29)and 16.7%(6/36),respectively.These results showed that the risk points of pseudorabies mainly concentrated in the second trimester of pregnancy and fattening stage of 60-100 days.2.Laboratory testingIn order to find out the main causes of wheezing in fattening pigs,diarrhea of newborn piglets and abortion of pregnant sows.In this study,40 samples were collected(8 fattening pigs,16 piglets and 16 aborted fetuses).Real time PCR was used to detect the pathogens in clinical samples of pigs in this large-scale pig farm,The positive rates of PRV and PCV2 were 80% and 30% respectively.Combined with clinical manifestations,It can be concluded that PRV is the main cause of the disease.Then,the g E Gene of PRV wild virus detected from the pig farm was amplified,sequenced and analyzed for genetic evolution.The results showed that the PRV wild virus in the large-scale pig farm belonged to the Asian isolate gene type 2.3 variant.It has the highest homology with the newly isolated SMX2012、GD-FS-2014、GD-JM-2015、He N1-2012、HN1201-2012、HNX-2012 、 HLJ8-2013,up to 99.8%.However,Bartha-K61 strain of Pseudorabies Vaccine Used in this farm belongs to the genotype 1 of European and American classical strains,and the homology is only 97.4%,which is relatively poor.PRV-GE antibody tests were performed on sows,nurseries and fattening pigs at all stages of production.The results showed that the positive rate of PRV-GE antibody was as high as 30.5%(175/574),15.4%(44/286)and 25.5%(83/324),respectively,in sows,nurseries and fattening pigs.At the same time,PRV-GE antibody was detected and the pig population samples at all stages were randomly selected for neutralizing antibody detection.PRV wild virus strains isolated from this field were used as the detection viruses for neutralizing antibody test.The results showed that the neutralizing antibody positive rate of sows was 54.9%(50/91).The positive rate of neutralizing antibody was 38.0%(38/100).The positive rate of neutralizing antibody in serum was 52.8%(56/106).The level of neutralizing antibody in serum in pig herds at all stages was low,and the positive rate of neutralizing antibody was below 60%.3.Immune program adjustment and effect analysisThe prevalence and disease of pseudorabies in this pig farm have an important influence on the production results.According to the actual production needs,the immunization procedure of pseudorabies vaccine was adjusted.The vaccine selection was based on the genetic evolution of pseudorabies virus for emergency immunization with live pseudorabies gene deletion vaccine(HB-2000 strains)and pig pseudorabies inactivated vaccine(A strain),which were more closely related and homologous.By optimizing the pseudorabies immunization program of this pig farm,and comparing and analyzing the PRV neutralizing antibody and PRV pathogen positive rate of sows,nurseries and fattening pigs before and after optimization,it was found that the neutralizing antibody positive rate of pigs at each stage after optimization was significantly increased(P<0.05).It was 54.9%(50/91),38.0%(38/100)and 52.8%(56/106)before optimization.It was optimized to be 88.0%(88/100),80%(80/100)and 75.0%(75/100).The positive rate of PRV in each pig group was significantly reduced(P<0.05)(Before optimization:30.5%(175/574),15.4%(44/286)and 25.6%(83/324);Optimized: 20.3%(81/400),7.8%(22/282)and 9.2%(30/326)).Statistical analysis was also conducted on the relevant production data and clinical indicators before and after the optimization of immune procedures.The results showed that the abortion rate of sows,stillbirth rate of sows,mortality rate of piglets in the delivery room and mortality rate of finishing pigs decreased from 13.2%(25/190),12.5%(25/200),10.3%(204/1981)and 8.4%(130/1550)before optimization to 2.1%(4/190),3.6%(7/194),4.7%(89/1894)and 3.3%(50/1550),respectively.The difference is significant.In terms of production performance,the optimized PSY and MSY increased from 20.3 and 18.7 before optimization to 22.2 and 21.5,with significant differences.The optimization of immunization procedure has a significant effect on the improvement of the pig farm production performance.4.Comprehensive prevention and control measuresStandardizing biosafety system plays an important role in prevention and control of disease ofter after the adjustment of immunization program.Therefore,we improve the following aspects of biosafety measures to the pig farm.First,strengthen external biosafety management,such as pigs,personnel,vehicles,material aspects.Second,formulate the on-site biosafety management system and improve the disinfection process of carrying pigs and empty bars.Third,strengthen feeding management,adhere to all in all out,implement batch production management.Fourth,standardize the operation of vaccine immunization and strictly follow the adjusted immune program.In summary,based on the results of epidemiological investigation and pathogenic detection,our results demonstrated the type of pseudorabies virus strain in the pig farm and its distribution and transmission in various pig herds,revealed the detoxification law of sows and growing pigs at different stages,and determined the risk points of this pig farm.In order to solve the actual production problems of this pig farm,we screened the targeted vaccine according to the genetic evolution relationship analysis,adjusted the immune program in time and formulated comprehensive prevention and control measures to realize the prevention and control of pseudorabies and significantly improve the production performance in the pig farm. |
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