| Pseudorabies?PR?is an acute infectious disease caused by Pseudorabies virus?PRV?.PR first happened in the United States in 1813.It has been reported in more than 50 countries around the world.At present,the PR has been controlled and eradicated in some European countries by utilizing gene deletion vaccine and detecting wild strain antibody by ELISA.This method is widely used in most pig farms in China,as a result,the epidemic transform regional epidemic to sporadic,and the incidence rate is significantly decreased.However,in recent years,this disease shows an increase trend,indicating that the situation of wild-virus infection is still serious.In order to understand the PR wild-virus infection in scaled pig farms in Hunan Province,4288 seral specimens of pig were collected from the vaccinated swine herds from 14 regions of Hunan Province.The levels of PRV gE and gB antibodies were tested by ELISA method.The results showed that the field positive rate of PRV gE antibody was 21.0%?81/208?in 208 scaled pig farms,and the individual positive rate was 38.9%?901/4288?;While,the field positive rate of PRV gB antibody was 64.6%?102/157?in 157 PRV immunized pig farms,and the individual positive rate was78.1%?2233/2858?;Moreover,the positive rate of PRV gE antibody was the highest in the large pig farms which with more than 1000 pigs,the rate was 22.9%.The positive rate of PRV gE antibody showed the highest level in summer,which was25.1%.As for the different growth stages,the result showed sows had the highest positive rate of PRV gE antibody,which was 36.2%.These data indicates that PR is still widely spread in Hunan Province,and the wild-virus infection of PRV was more common.In the present study,several clinical cases were primary diagnosis as PR according to the clinical symptoms and anatomical pathological changes.Then tissues including brain,liver,kidney,and lymph nodes were collected from these dead pigs,and PRV wild-type infection were further confirmed by using PCR assay.Two wild strains of PRV were isolated and named as HN-YY and HN-NX,their virus titers were 10-7.7/0.1 mL and 10-7.75/0.1 mL,respectively.The 9 genes of gB,gH,gL,gI,gM,gG,gE,TK and PK of the two isolated PRV wild strains were amplified by PCR and sequenced.The results from sequence analysis showed that the isolated PRV strains shared a high identity with those of several PRV isolations strains at home and abroad.The gene phylogenetic tree was made to further analyse the genetic variation of the two strains.The results showed that the amino acid sequence of the gE gene of the HN-YY was found to have a deletion of aspartic acid?Asp,D?at position 491;the amino acid sequence of gG gene was mutated at position 177 for glutamate?Glu,E?to glycine?Gly,G?,and at position 329-366 has an amino acid insertion?SPAAPVEGAGDGEEGHGDEEDEELTSSDLDNIEIEVVG?.The amino acid sequence of the HN-NX gE gene was mutated at position 562 from tryptophan?Trp,W?to threonine?Thr,T?.The results of genetic evolution analysis showed that the two strains of PRV isolated in this study belong to the same branch of the domestic reference strains,while the foreign reference strains were in another branch,indicating that the two strains have small variation and are closely related to the domestic strains.Those results can provide a scientific basis for the development of PR prevention and control measures in Hunan Province. |
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