| In recent years,the outbreak of Cyprinid herpesvirus 2(CyHV2)in fection in crucian carp resulted in a tremendous economic loss in aquaculture.This virus has been reported worldwide and has attracted more and more attention in china,especially in Jiangsu province.Besides CyHV2,Aeromonas hydrophila can cause haemorrhagic septicaemia in crucian carp.In 2015,crucian carp(Carassiuscarassius)in some farms of Nanjing showed symptoms of haemorrhagic septicaemia.Forty-two samples from ten fish ponds were collected and pathogens were investigated.Bacteriological investigation showed that twenty-eight Aeromonas isolates were identified to species levels based on sequencing of the housekeeping gene gyrB,including six strains of A.veronii,eleven strains of A.jandaei,three strains of A.sobria and eight strains of A.hydrophila.The detection results for CyHV2 infection showed that thirty-four samples were proved of being CyHV2-positive,including twenty-six from diseased fish and eight from healthy fish.It is noteworthy that seven samples were positive for both CyHV2 and A.hydrophila,while only one sample was negative for both pathogens.It suggests that CyHV2 and A.hydrophila were the main pathogens causing hemorrhagic disease of crucian carp in Nanjing.On the basis of pathogen identification,CyHV2-positive samples were used for purifying this virus by applying differential centrifugation and sucrose gradient centrifugation and then electron microscope was applied to observe the morphology of virions.The results demonstrated that virions could be observed in different concentrations of sucrose solutions,while the concentration and purification of virions were highest in the interface between 25%and 35%sucrose solution and in 35%sucrose solution.To identify the antigenicity of envelope protein of CyHV2,the recombinant plasmid pET32a-ORF30 was constructed and then it was transformed into the competent cell.After this,pET32a-ORF30 fusion protein with the molecular weight of 65kD was purified via HisTrapTMHP.The pET32a-ORF30 fusion protein and the purified virus were respectively injected into ICR mice and New Zealand rabbits.The indirect ELISA method demonstrated that the titres of sera were above 1:12800.Western blot analysis showed good reactinogenicity with the serum against purified virus.This study indicated that this fusion protein have good antigenicity,which provides an establishment of detection methods of CyHV2 and development of subunit vaccines. |
