Evaluation of changes in the epidemiology of leptospirosis in dogs after introduction of a quadrivalent antileptospiral vaccine in a highly endemic area

Background - Since 2003, a marked increase in leptospirosis serogroup Australis has been observed in dogs in Switzerland. In 2013, a new quadrivalent antileptospiral vaccine (L4) was introduced, adding serogroups Australis and Grippotyphosa to Canicola and Icterohaemorrhagiae of the previous bivalent vaccines (L2). Objective - To examine whether introduction of L4 was associated with decreased incidence of leptospirosis and decreased odds for dogs with acute kidney injury (AKI) to be diagnosed with leptospirosis. Animals - Four hundred and sixty‐nine dogs with AKI presented to a referral hospital, including 269 dogs with leptospirosis and 200 controls with other causes. Methods - Descriptive section: disease incidence was evaluated for 3 consecutive periods: before (PRE, 2011‐2012), transition (TRANS, 2013‐2014), and after introduction of L4 (POST, 2015‐2017). Analytical section: variables associated with a diagnosis of leptospirosis were investigated in a case‐control study using multivariable logistic regression, and focusing on vaccination. Results - The number of dogs diagnosed with leptospirosis (AKI‐L) decreased from 56.5 (PRE) to 15.7 (POST) cases/year while controls increased from 16.5 to 38.0 cases/year. Control dogs (AKI‐nL) showed a decrease in L2 vaccination (100% to 26%) and an increase in L4 vaccination (0% to 70%). The odds ratio for vaccinated dogs to be diagnosed with leptospirosis was 0.11 (95% confidence interval [CI], 0.06‐0.22; P < .001) for L4 and 2.08 (0.58‐7.42; P = .26) for L2. Conclusions and Clinical Importance - The introduction of L4 was associated with a marked decrease in dogs with leptospirosis and AKI in Switzerland. Use of the L4 vaccine was associated with significantly decreased odds of disease