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

backgroundSince 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).

objectiveTo 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.

methodsDescriptive 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.

resultsThe 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.