The Adaptation Of Canine Distemper Virus To Human SLAM Receptor And Immunogenicity Of Canine Distemper Inactivated Vaccine

Canine distemper?CD?is a high infectious disease caused by canine distemper virus?CDV?.CDV is highly valued because of the high morbidity and mortality of the infected animal which has broad host range.CD has various clinical symptoms such as fever,conjunctivitis,neurological symptoms.Secondary infections in the middle and late stages of the disease are caused by bacteria.CDV traditional hosts include Canidae,Mustelidae,Procyonidae and Viverridae.In recent years,however,CD has broken worldwide and the cross species spread of CD has attracted people's attention.CDV H protein as the viral receptor recognition protein is also the most frequently mutated protein.The antigen drift caused by H protein mutation is the reason of CDV outbreaks.Some studies have shown that the mutation of CDV H gene causes the virus adapted to the new host,macaque.Therefore,CDV may break through the host barrier to infect humans by SLAM receptors and CDV may pose a threat to human public health security.In this study,recombinant CDV 5804Pe strain expressing green fluorescent protein?eGFP?was serially passaged on Vero cells expressing human SLAM receptor?Vero-hSLAM,VHS?and obtained a strain which can rapidly adapt to human SLAM receptor.Sequencing of the viral H gene revealed that the use of the human SLAM receptor requires a change in amino acid position 540 of the H gene,mutation of aspartic acid?D?to glycine?G?.The eukaryotic expression vector of constructing mutants and cell fusion experiments show that CDV can be adapted to human SLAM by only one amino acid change.Through the Whole-genome sequencing of the CDV 5804Pe strain which adapted to hSLAM receptor?5804Pe-VHS?revealed that there are 3 amino acid mutations.CDV not only has the infectious risk for new hosts,but also poses new challenges to traditional hosts,especially threat to the immune prevent.CDV is an important pathogen in dogs,whose the natural mortality rates up to 80%.The young dogs are most susceptible to CDV.Currently,vaccination is considered to be the safest and most effective way to prevent CD.The traditional canine distemper vaccine was developed in the 1950s and1960s and has made great contributions to CDV prevention in worldwide.However,some canine distemper vaccines with low safety still have residual virulence to wild animals?Pandas,red pandas,ferrets,etc.?Secondly,the traditional live vaccine has been questioned about the immune protection effect of animals while the CDV shows frequent antigenic variation.Therefore,it is necessary to maintain good immune protection effects of canine distemper vaccine by developing new safe and efficient vaccines?including attenuated vaccines?.Immunological adjuvant is an important component of inactivated vaccine,which can improve the immunogenicity of inactivated vaccine,induce the host to produce long-term high-level immune response and enhance the immune effect.Therefore,canine distemper inactivated vaccine is one of the current research highlights.In this study,the CDV wild strain(10^6.0TCID₅₀/mL)was inactivated by?-propiolactone,and an inactivated vaccine was prepared by adding different vaccine adjuvant.The immunization was performed three times for the young Beagle dogs and then dogs were infected by CDV virulent strains.Evaluate of immune effect about three adjuvants?MONTANIDE GEL 02,ADJ-801 and Al?OH?₃?by neutralizing antibody assay,clinical symptom observation,collecting nasal and rectal swabs and detect viral load in tissues.The results confirmed that the inactivated vaccine made by MONTANIDE GEL 02and ADJ-801 adjuvant can significantly enhance the immune response of CDV vaccine in beagle dogs.The titer of neutralizing antibody after the third immunization was 10.6 and40.2,respectively.On the 14^thh day,the neutralizing antibody titers reached 512,the protection rates were 80%and 100%,respectively.Our results could provide research materials for CDV prevention and control.