Risk of infection in dogs in contact with clinical canine leptospirosis cases

Canine leptospirosis cases have been increasing since the disease emerged in urban Sydney in 2017. Clinical infection is associated with a high case fatality rate and might pose public health risks. This study was conducted to determine whether Leptospira spp. exposure of healthy dogs in contact with clinical cases is a risk for leptospirosis infection.

In-contact (exposed) dogs were identified from clinical leptospirosis cases and prospectively enrolled. In-contact dogs underwent leptospirosis testing by polymerase chain reaction (PCR) and microscopic agglutination test (MAT). An historical comparison population of dogs unexposed to clinical leptospirosis cases was selected from a previous seroprevalence study, from which exposure status and MAT titres were available. Dogs were excluded from analysis if they had a prior history of leptospirosis vaccination or did not have MAT performed. An ordinary logistic regression model was used to estimate the prevalence odds ratio of infection given exposure. Potential confounding by age, sex and neuter status was assessed.

Exposure to a dog with clinical leptospirosis was significantly associated with an increased risk of infection (P < 0.05). The odds of becoming infected with canine leptospirosis were five times greater for dogs exposed to clinical cases than for dogs not known to have been exposed (OR 5.0, 95% CI: 1.3-20.0). This association was not confounded by age, sex or neuter status.

These findings support the prophylactic use of antimicrobials in dogs that have been in contact with dogs with clinical leptospirosis.