Antibody titres against canine distemper virus in vaccinated and unvaccinated dogs

In 248 urban dogs the serum antibody titre against canine distemper virus (CDV) was determined by the immunoperoxidase monolayer assay. Among them 72 animals had been routinely vaccinated at least once against distemper, 20 dogs had never been immunized and the vaccination history of 156 was unknown. The mean antibody titre in vaccinated dogs (114 +/- 8.2) indicated immunity (greater than or equal to100) and was significantly higher when compared with unvaccinated animals (29 +/- 8.8, P < 0.05) or with dogs with unknown vaccination history (29 ± 5.0. P < 0.001). Among 156 dogs with unknown vaccination history only 26 (19%) had antibody titres indicating immunity against CDV (greater than or equal to100). Vaccinated dogs were divided into five groups according to the time since the most recent distemper vaccination: group A: up to 1 month (n = 13) group B: 1-2 months (17 = 6); group C: 2-12 months (n = 20); group D: 12-24 months (it = 4); group E: 25-36 months (n = 9) and group F: 36 or more months (n = 18). The mean titre in group A was 490 +/- 4.5, in B 359 +/- 3.8, in C 204 +/- 4.6. in D 269 +/- 1.9 and the differences between these groups were not significant. However, dogs in groups E and F had significantly lower mean antibody titres (21 +/- 8.3 P < 0.01 and 39 ± 7.6. P < 0.001, respectively) when compared with group A. Nine dogs suffering from distemper confirmed by the immunofluorescence test or nested RT-PCR were also included in this study. In five of them high titres of anti-CDV antibody were detected (160-1280). All these animals recovered (in two localized muscle twitching persisted). On the contrary, the remaining four patients with low antibody titre to CDV (5-40) died.