This research was done in order to elucidating whether the simultaneous injections of rabies and DHP (Distemper, Hepatitis, and Parvovirus) vaccines in dogs is accompanied with the antigenic competition and suppression of the rabies antibody titer or not.

This study was carried out on 54 owned dogs which were not given any vaccine before. The mentioned dogs were randomly assigned to three groups. The first group received rabies vaccine¹ only, the second group received rabies and DHP² vaccines simultaneously, and the third group received rabies and then DHP vaccines with two-weeks interval. Blood samples were taken and the neutralizing rabies antibody titers were measured by RFFIT (Rapid fluorcent focus inhibition test) method on the fourteenth and sixtieth days after the injection of rabies vaccine in the all animals of the three groups. Analysis of data was done by one-way ANOVA method.

On the day 0 (before rabies vaccination) the rabies antibody titers in all dogs of the three groups were 0. On the day 14^th the mean and standard deviation of rabies antibody titers were 9.0857±6.1641, 13.1389±6.5828, and 9.4722±6.0042 in the groups 1,2, and 3 respectively, and on the day 60^th the mean and standard deviation of rabies antibody titers were 5.2533±4.8147, 5.9615 ±2.97, and 7.3941 ±5.2680 in the groups 1,2, and 3 respectively. No significant differences were found between the rabies neutralizing antibody titers of 3 groups in both sampling times and all the measured titers were more than the least protective antirabies antibody titer, defined by WHO (0.5 iu/ml).

Reduction of immunogenicity mediated by the interaction of various fractions in a vaccine is described as antigenic competition. Antigenic competition is defined as the reduction of the immune response to one antigen as a result of an immune response to a second unrelated or related antigen; therefore, as a general rule, for multivalent vaccines or in the case of simultaneous administration of different vaccines, the absence of interference with the efficacy of each vaccine must be established. Since in this study no significant differences of rabies antibody titer were observed between three groups, in order to facilitate vaccination protocol and save both time and money, we may recommend simultaneous using of rabies and DHP vaccines without concerning about the probability of suppression of rabies antibody response caused by antigenic competition mechanism.

References

1.  Taussig, M.J., 1973.Curr.Top.Microbiol.Immunol. 60: 125-174.

2.  Jolivet, M., et al, 1990, Vaccine, 8: 35-40.