Fifteen-month duration of immunity for the serovar Grippotyphosa fraction of a tetravalent canine leptospirosis vaccine.

Forty-four specific pathogen-free beagles, median age 65 days, received two subcutaneous doses of either a commercially available, five-way combination vaccine or the same vaccine in combination with a tetravalent bacterin (Canicola, Grippotyphosa, Icterohaemorrhagiae, Pomona). They were subsequently challenged with a pathogenic strain serovar Grippotyphosa 470 days following completion of the vaccination protocol. Titres of agglutinating serum antibodies were determined at various time points before and after both vaccination and challenge, along with postchallenge reisolation of the challenge organisms from blood and urine, and evaluation of renal histopathology. Clinical signs of generalised leptospirosis were not observed in any of the dogs after challenge. In order to demonstrate efficacy, leptospirosis was defined as having at least one positive urine sample and a positive renal histopathology score; or, in the absence of renal pathology, multiple positive urine samples. Leptospiremia was not demonstrated in any of the vaccinated dogs versus 27 per cent of the controls; leptospiruria was noted in 5 per cent of the vaccinates compared with 76 per cent of controls; and renal lesions were observed in 15 per cent of the vaccinates and 65 per cent controls. Using these criteria, the vaccine was able to significantly prevent leptospirosis (P=0.0001) in the vaccinated animals. This study establishes duration of immunity of at least 15 months for the prevention of disease and renal excretion of leptospires for the serovar Grippotyphosa fraction of a quadrivalent vaccine.