Aims: To evaluate the serological response in dogs to a commercial vaccine for use in cattle containing cultured strains of Leptospira interrogans serovars Copenhageni and Pomona, and L. borgpetersenii serovar Hardjo.
Methods: Blood samples were obtained from 67 working farm dogs on 12 farms, and the microscopic agglutination test (MAT) was used to measure titres to the Leptospira spp. serovars Pomona, Hardjo, and Copenhageni. Samples with a titre of <1:25 were defined as seronegative. Dogs that were seronegative to both Pomona and Hardjo (n=33) were randomised to either the vaccination (n=20) or control (n=13) groups. Seven of these dogs were seropositive to Copenhageni. Vaccinated dogs were given the three-component vaccine subcutaneously on two occasions, 4 weeks apart. MAT titres were measured again in both groups 2 weeks after the second vaccination.
Results: Of the vaccinated dogs, 20/20 (100%) developed titres to serovar Pomona, and 16/20 (80%) had titres >100; for serovar Hardjo, 19/20 (95%) dogs had titres, with 18/20 (90%) being >100; and for serovar Copenhageni, 15/17 (88%) dogs that were initially seronegative had titres, with 6/17 (35%) being >100. The median titres for Pomona and Hardjo (200 (95% CI=179-359) and 200 (95% CI=176-379), respectively) were lower than for Copenhageni (50 (95% CI=26-124)) in dogs originally seronegative (p<0.001). There was no association between titres to the different serovars. Of the 13 unvaccinated dogs, two developed titres to serovar Pomona, and three to Hardjo. All titres were <100.
Conclusions: The tested vaccine was effective in raising antibodies to the three serovars, although the titres do not guarantee protection.
Clinical relevance: There has been a recent increase in cases of leptospirosis attributed to the serovar Pomona in dogs in New Zealand, but the vaccines licensed for use in dogs in New Zealand for the prevention of leptospirosis only protect against Copenhageni/Icterohaemorrhagiae. The vaccine tested in this study produced titres to Pomona and Hardjo that suggest the vaccine could be useful for reducing disease caused by these serovars in working dogs in New Zealand.