Induction of virus neutralizing antibodies against canine distemper virus: towards an effective vaccination strategy for tigers

Critically endangered tiger populations are at risk from infection with canine distemper virus (CDV). As field studies in the Russian Far East have indicated that CDV circulates in wild carnivores as well as domestic dogs, it... [ view full abstract ]

Critically endangered tiger populations are at risk from infection with canine distemper virus (CDV). As field studies in the Russian Far East have indicated that CDV circulates in wild carnivores as well as domestic dogs, it is unlikely that vaccination of domestic dogs alone would be sufficient to prevent cross-species infection of Amur tigers. Hence, the most effective strategy to prevent the infection of tigers would be to vaccinate the tigers themselves. In order to assess the likely efficacy of such a strategy, we developed a vesicular stomatitis virus (VSV)-based virus neutralising antibody (VNA) test based on field strains of CDV in the Russian Far East. Sera collected from vaccinated UK dogs were compared with sera from unvaccinated dogs from the Russian Far East. While the Russian dog convalescent sera displayed potent neutralisation of the field strains of CDV, UK vaccinated dog sera displayed a degree of strain specificity. However, as both serum sets displayed good neutralising activity, we could be confident that existing CDV vaccines would elicit protective immunity against field strains of virus. We then extended our analyses to include sera from captive tigers vaccinated with either of two commercial CDV vaccines. Vaccination of the tigers with a modified live virus vaccine induced potent VNA titres after a single vaccination, the antibody titres being comparable initially to those of either vaccinated or naturally exposed dogs and then decreasing significantly six months later. In comparison, VNA were not detected in animals vaccinated with a canarypox vectored vaccine until after a booster vaccination one month later. While it is not possible from these data to predict protective titres for CDV in the field, the data confirm that both vaccines are capable of inducing cross-neutralising antibodies against vaccine and field strains of CDV and might be suitable for future vaccination campaigns.