Pathogenic And Serological Detection And Analysis Of PRRS In Four Large-Scale Pig Farms In Nanning,Guangxi

Porcine reproductive and respiratory syndrome virus（PRRSV）has caused serious economic losses to the pig industry.Vaccination is the main means to prevent and control the disease.However,due to massive use of weak vaccines,increasing natural infection as well as continuous evolution and mutation of PRRSV strains,clinical prevention and control has become more difficult.In recent years,PRRS have occurred frequently in Guangxi.In order to know the situation of PRRSV infection in large-scale pig farms in Guangxi.In this study,molecular epidemiological and serological investigations were conducted on samples from four partial scale pig farms in Nanning,Guangxi in 2022.And then we followed up and analysed them continuously to understand the epidemiological dynamics of PRRSV and antibody levels of pig groups in the region.In order to further study the epidemic characteristics,genomic characteristics and infection status of PRRSV,and provide reference for the subsequent accurate prevention and control of PRRS.1.Etiological investigation of PRRSV in four large-scale pig farms in Guangxi Zhuang Autonomous Region in 2022In this study,14,942 samples were collected from four large-scale pig farms in Nanning,Guangxi in 2022.The average positive rate of PRRSV was 8.65%（1292/14942）.Further analysis of the positive effects of PRRSV on pig farms by farm,season and pig groups showed that there were significant differences in the positive detection results of PRRSV among pig farms.The positive rate of PRRSV in Longan pig farm was significantly higher than that in Hengzhou and Shuangding pig farms.There were more farmers around Longan pig farm and it was close to the highway,suggesting that pig farms should be located scientifically.The positive rate of PRRSV in fattening pigs was significantly higher than that in other pigs,suggesting that immunization should be strengthened for this part of pigs.The positive rate of PRSSV in the fourth quarter was significantly higher than that in the second and third quarters,suggesting that pig insulation and biosafety prevention and control should be strengthened in the autumn and winter.In order to further study and investigate PRRSV strain types in pig farms,23 PRRSV ORF5sequences and 18 NSP2 sequences were successfully obtained from 1292 positive samples whose CT value was less than 23.Sequence homology analysis showed that they were all PRRSV-2.Genetic evolution analysis of these nucleotide sequences based on ORF5 and NSP2 evolutionary tree showed that NADC30-like was the main epidemic strain in the pig farm under investigation.The comparison results of 23 ORF5 amino acid sequences showed that 137 aa was S,that is,all 23 PRRSV strains in this study were wild strains.R¹³→Q¹³/P¹³and R¹⁵¹→K¹⁵¹mutation occurred in all strains except 202203 and 202204.In addition,22 of the 23 PRRSV strains had conservative N-glycosylation sites（44 aa and 51aa）in GP5 protein,and different mutations occurred at 30 aa,32 aa,33 aa,34 aa and 57 aa,and the number of N-glycosylation sites showed an increasing trend.The deletion pattern of 18 NSP2 amino acid sequences was consistent with that of NADC30（1+19）.2.Serological investigation of PRRSV in four large-scale pig farms in Guangxi Zhuang Autonomous Region in 2022Serological analysis after injection of PRRS vaccine was conducted to obtain the prevention and control effect of PRRS vaccine on the disease.The results of serum collection are as follows:In 2022,a total of 1,908 serum samples were tested from four large-scale pig farms,of which 1,746 were positive.The total positive rate of PRRSV antibody in the whole year was 91.51%,but the level of PRRSV antibody was inconsistent.Combined with the results of PRRSV etiology,the results showed that PRRSV infection existed in each field to a certain extent.The difference analysis of PRRSV antibody positive rate of different breeding farms showed that the difference of PRRSV antibody positive rate of the four farms was not significant（P>0.05）,but the positive rate of PRRSV antibody reached the national regulation level（≥70%）.The positive rate of PRRSV antibody in the second quarter was significantly lower than that in the first quarter（P<0.05）,but there was no significant difference among other quarters（P>0.05）.The positive rate of PRRSV antibody in breeding boars was significantly higher than that of gilts and Suckling piglets（P<0.05,P<0.001）,but had no significant difference compared with that of parroting sows and finishing pigs（P>0.05）.There was no significant difference in PRRSV antibody among other pig groups（P>0.05）.Mainly due to the environmental conditions and prevention and control measures in different regions.Therefore,in the actual breeding and production of pig farms,prevention and control measures in line with the actual situation of each farm should be formulated according to the local environmental conditions and prevention and control situation;Secondly,when PRRS immunization is carried out in livestock farms,the safety and quality of vaccines must be strictly controlled,the law of the rise and fall of vaccine immune antibodies must be mastered,and the negative groups should be supplemented and exempted in time.Finally,during the investigation,it was found that the Hengzhou pig farm did not strictly disinfect and change the syringe needle between different litters in the process of vaccine injection.Education should be strengthened,disinfection measures should be improved,and feeding management should be improved,so as to improve the disease resistance of pigs,so as to ensure the health and safety of pigs.In Conclusion,at present,there are four large-scale pig farms keep a comparatively higher immunization level against PRRSV.However,PRRSV has been detected in epidemic status in all quarters.The sequencing results of ORF5 and NSP2 genes showed that NADC30-like strain was the main circulating strain in this region.This study enriched the epidemiological monitoring data of PRRS in Guangxi,and provided data reference for subsequent epidemic purification and immunization prevention and control.