The humoral immune response to recombinant nucleocapsid antigen of canine distemper virus in dogs vaccinated with attenuated distemper virus or DNA encoding the nucleocapsid of wild-type virus

This study compared the humoral immune response against the nucleocapsid-(N ) protein of canine distemper virus (CDV) of dogs vaccinated with a multiva lent vaccine against parvo-, adeno-, and parainfluenza virus and leptospira combined with either the attenuated CDV Onderstepoort strain (n = 15) or a n expression plasmid containing the N-gene of CDV (n = 30). The vaccination s were applied intramuscularly three times at 2-week intervals beginning at the age of 6 weeks. None of the pre-immune sera recognized the recombinant N-protein, confirming the lack of maternal antibodies at this age. Immuniz ation with DNA vaccine for CDV resulted in positive serum N-specific IgG re sponse. However, their IgG (and IgA) titres were lower than those of CDV-va ccinated dogs. Likewise, DNA-vaccinated dogs did not show an IgM peak. Ther e was no increase in N-specific serum IgE titres in either group. Serum tit res to the other multivalent vaccine components were similar in both groups .