Epidemiological Investigation And Detection Of Epidemic Strains Of Pseudorabies In Shandong Province

Porcine pseudorabies is an acute infectious disease of pigs caused by Pseudorabies virus?PRV?.It can cause reproductive failure of sows and a large number of deaths of piglets,which has seriously harmed the healthy development of pig industry in China for a long time.Especially after 2012,the Bartha-K61 vaccine immunized pigs in various parts of China have a large-scale outbreak of pseudorabies or wild-type infection,and the breeding traits of pigs in the affected farms have increased reproductive mortality and piglet mortality.This study is mainly based on the detection of samples and serum from January 2017 to December 2018.In the past two years,723 samples of pathogen samples and 8868 samples of serum samples were received.According to the structure,region and season of pigs,The samples were classified and the system was tested by pathogens and serology to explore the prevalence of the disease in Shandong in the past two years,and the variation evolution and virulence of the isolated strains were detected and analyzed.Epidemiological surveys of pathogens and serology showed that in the 723 clinical samples in 2017,82 pathogens were positive by PCR,and the positive rate was 11.20%?82/732?,of which the first,second,third,The positive rates in the fourth quarter were17.48%,8.37%,10.06%,and 11.06%,respectively.Of the 557 clinical samples in 2018,42were positive for pathogens by PCR,and the positive rate was 7.54%?42/557?.The positive rates in the first,second,third and fourth quarters were 13.37%,2.87%,5.22%and 8.33%,respectively.The pathogen test results showed that the disease had obvious seasonality,and the winter and spring cold seasons were frequent and from 2017.By 2018,the positive rate of the disease in Shandong is generally decreasing.In addition,the investigation found that other suspected pseudorabies death animals?dogs,rabbits,cats,cattle,and sheep?around the farm and inside the farm were mostly negative by PCR,indicating that the incidence of pseudorabies in other animals was extremely low.The PRVgE antibody test showed that4,558 copies were positive in 5668 serum,accounting for 52.58%.According to the cluster statistics,the positive rate of antibody in gilts in 2017 is 40.91%,which is related to the importance of seed testing in pig farms.The highest antibody positive rate in boars in 2018 is69.69%.The positive rate of antibody in sows is Production parity is directly proportional.Sixteen strains of PRV were isolated from positive samples.The genetic tests showed that the strains isolated from this study had high homology with domestic strains and belonged to the same branch in genetic evolution,which was significantly different from European and American reference strains.All domestic strains?including the isolates of this study?have a large number of amino acid mutation sites on the hydrophobic residues and hydrophilic residues of gE glycoprotein,and they occur on hydrophilic residues.Many different amino acid site mutations.In the dominant epitope of gB gene,domestic epidemic strains and European and American reference strains still have a large number of identical amino acid site mutations,and the most popular strains in China are TA1 and TA2.The amino acid site mutation of the TK gene is less,which is related to the high conservation of its gene,and there is no significant feature in the genetic evolution relationship.The in vitro and in vivo virulence test results of two strains isolated from this study?Jinan strain-JNP,Taian strain-TA1?showed that the TCID₅₀0 and LD₅₀0 of JNP strain were10^7.71TCID₅₀/mL and 10^5.07LD₅₀/mL,respectively,TA1 strain TCID₅₀0 and The LD₅₀0 was10^7.23TCID₅₀/mL and 10^5.01LD₅₀/mL,respectively.The two strains had strong pathogenicity and no significant difference between them.The distribution of the virus showed that the brain content of the mouse was the highest,followed by the liver,and the content of each organ of the TA1 strain was significantly higher than that of the JNP strain.Therefore,we can conclude that there are several characteristics of pseudorabies in Shandong:1 widespread in large-scale pig farms and high infection rate;2 isolated strains have higher homology with domestic strains.Sex,but some antigenic epitopes are mutated;3 epidemic strains have strong pathogenicity.Therefore,in the prevention and control of pseudorabies in pig farms in China,it is extremely urgent to study high-efficiency vaccines that meet the antigenic characteristics of epidemic strains and to develop reasonable farm immunization procedures and rigorous pseudorabies purification programs.