This prospective study sought to determine the antibody response of dogs to commercially available quadrivalent Leptospira vaccines containing the serovars canicola, grippotyphosa, icterohemorragiae, and pomona. Healthy client-owned dogs (n = 32) with known vaccination history and no Leptospira spp vaccination in the previous year were randomly assigned to receive 1 of the 4 commercially available quadrivalent vaccines at weeks 0 and 3. Booster vaccines were given to 25/32 dogs at week 52. Antibody titers to serovars bratislava, canicola, grippotyphosa, hardjo, icterohemorrhagiae, and pomona were determined by microscopic agglutination test (MAT) on weeks 0, 3, 4, 7, 15, 29, 52, and 56. MAT titers ≥1:100 were considered positive.
Highly variable antibody responses were detected between and within vaccine groups. Highest MAT titers (≥1:800) were detected at weeks 4 and 56. However, most dogs were seronegative for many serovars by week 15, and most were seronegative for all serovars at week 52. At week 56, only canicola was associated with MAT titers >1:100 in >50% of dogs, regardless of vaccine. Some dogs developed positive MAT titers to bratislava or hardjo, which were not contained in the vaccines. Previous challenge studies have demonstrated duration of immunity for commercial Leptospira vaccines to be ≥1 year, with vaccinated dogs protected from clinical disease and renal carrier state for 12 or 14 months, suggesting that MAT titers are not well-correlated with duration of immunity of vaccines against natural infection. Furthermore, MAT titers have poor specificity for distinguishing vaccinal titers from natural infection. Study funded by IDEXX Laboratories.
