Prevention of severe clinical signs and pathological lesions of leptospirosis in experimentally challenged dogs

ABSTRACT

Objective: To prevent severe clinical and pathological findings of leptospirosis in dogs vaccinated against L. interrogans serovar Copenhageni. Design and Methodology: Two vaccination-challenge experiments involving 22 dogs were performed using a vaccine prepared from formalin-killed cultures of L. interrogans serovar Copenhageni. The dogs were challenged by administering a suspension of 1 x 109 of a virulent strain of serovar Copenhageni (8 mL) at 2 weeks (Study 1 Onset of immunity) and 14 months (Study 2 Duration of immunity) after primary and secondary vaccinations. Each dog was observed for clinical signs of leptospirosis for five weeks post-challenge (PC). Any dog which showed irreversible clinical signs of leptospirosis was humanely euthanized, and a necropsy performed. Results: One (20.0 %) vaccinated puppy in Study 1 showed mild clinical signs (PC) which lasted for one day. Five (100.0 %) non-vaccinated (controls) puppies exhibited irreversible signs of acute severe leptospirosis PC, as well as significant postmortem lesions consistent with leptospiral infection. In Study 2, no clinical signs were exhibited by the vaccinated group of dogs PC, while two (40.0 %) non-vaccinated dogs exhibited mild clinical signs for 2 to 3 days, after which they recovered. Conclusions: The vaccine was successful in protecting vaccinated dogs against acute leptospirosis 2 weeks and 14 months after a vaccination schedule of two doses of the bacterin (primary and booster doses), since all vaccinated dogs were clinically normal after challenge with a virulent inoculum of serovar Copenhageni.