| Classical swine fever(CSF),caused by classical swine fever virus(CSFV),is a highlycontagious and deadly infectious diseases of swine>and defined as A type disease in our country.Although legal immune prevention measures were taken,the disease is still constantly popular across the country.And swine fever epidemic situation has become increasingly complex,the main point distribution is given priority to,typical cases is often and more cases of atypical swine fever.The disease mainly concentrated in the nursery an early fattern stage,sick pigs showed more general hot disease symptoms such as fever?anorexia,and incidence is high,mortality is not low;After sows infected more performance for a sexual reproduction syndrome,persistent infection,recessive infection and immune tolerance.When mixed with other pathogen infection,it can significantly aggravated the pig's conditions and increase the mortality.Similar epidemic disease occurred in a swine farm in Lai' Wu city in May 2015,the nursery pigs were characterized by high fever(40.8?41.5?),depressed ofspirit,inappetence,the inside of limbs and tip of ear were cyanosed.Routine treatments exhibitedlimited effects.To identify the infective pathogen,autopsy and histopathologywere performed,the virus were detected by PCR and were isolated and identified.Thecomplete E2 gene of CSFV were amplified,cloned,and sequenced.The autopsy andhistopathology examination indicated that the silk pigs showed typical CSF-related lesions,including hemorrhagic and necrotizing lymphadenitis,focal hemorrhagic infarction on the edge of spleen,viral encephalitis,intestinallymphatic tissue necrosis and solid membrane enteritis and others.The lesions indicated theinfection of CSFV,and bacterial infection was excluded.The PCR detection and virusisolation revealed that the detected specimen were only infected by CSFV,and only CSFV(named SDLW2015)were isolated in PK-15 cells.The complete E2 gene of the isolatedCSFV strain were cloned and sequenced.The results revealed that the E2 gene ofSDLW2015 was 1,119 nt in length and coded 373 amino acids.The similarity analysis ofnucleotide and amino acid sequences revealed that SDLW2015 strain shared a nucleotidesimilarity of 82.1%?96.3%and an amino acid similarity of 88.5%?97.6%with otherreference strains.When compared with 8 reference strains of various genotypes,SDLW2015strain shared the lowest nucleotide and amino acid similarities of 82.1%and 88.5%with HCLV strain(1.1 subgenotype).When compared with the subgenotype 2.1 strains,SDLW2015 strain shared higher nucleotide(91.8%?96.3%)and amino acid(93%?97.6%)similarities.The newly isolated strain shared the highest nucleotide(96.3%)and amino acid(97.6%)similarity with GXWZ02 strain(subgenotype 2.1b).Moreover,the SDLW2015 sharedhigher similarities of nucleotide and amino acid with subgenotype 2.1d when compared with2.1a or 2.1c,indicating that the 2.1b strains were more similar with 2.1d strains,and theseresults were in accordance with previous reports.We further constructed a phylogenetic treeusing SDLW2015 strain and other 27 reference strains.The results showed that the 28sequences were divided into three genotypes(1,2,and 3)including eight subgenotypes(1.1-1.4,2.1-2.3,3.4).Among the subgenotypes,subgenotype 2.1 can be further dividedinto four subgenotypes including 2.1a,2.1b,2.1c and a newly defined 2.1d.The SDTA2015strain isolated in this study were clustered into subgenotype 2.1b,and the strain showed greatdifferences between the classical Shimen strain(subgenotype 1.1)or the attenuated C-strainvirus(HCLV,subgenotype 1.1).Blood samples were collected when the pigs in this farm were all returned to health to evaluate the immune status and the immune effects.A total of 93 samples were collected and 74 samples were positive for anti-CSFV antibodies,resulting a positive rate of 79.57%.The pigs of different production phases showed various positive rates,the rates varied from 62.50%?87.50%.Among them,the levels of anti-CSFV antibodies of boars and sows were highest,while the nursery pigs shared the lowest positive rate.After a comprehensive diagnosis,the epidemic disease in this farm was caused by CSFV,and the virus were clustered into 2.1b subgenotype.The outbreak got quickly controlled with comprehensive prevention and control measures based on CSFV.Due to the limitations of this study,the molecular biological characteristics?antigenicity and virus virulence of the isolated strains are not further analyzed.In addition,after the outbreak under control,the farm adjustted the program of swine fever vaccine immunization,and the antibody testing results show that the new immune program can make pigs get better antibody levels,therefore,the immune status was improved significantly. |
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