Canine leptospirosis and environmental risk factors in coastal New South Wales, Australia (2021 – 2023)

Canine leptospirosis is a re-emerging zoonotic disease that has been long neglected in New South Wales (NSW), Australia. Clinical canine leptospirosis cases in Shoalhaven, southeastern NSW from October 2021 to May 2023 were analysed to examine associations between environmental factors and the local occurrence of canine leptospirosis. Poisson models (log-transformed canine population offset and adjusted for the Index of Economic Resources) of spatial (landscape factors adjusted for economic status) and temporal environmental factors (lagged weekly climate variables) were fit to the data. During the 2022 Australian winter, a significant spatio-temporal cluster of canine leptospirosis was detected near lakes, overlapping with the areas heavily flooded in March 2022. In areas surrounding case residential addresses, the rate of canine leptospirosis was increased by the presence of nature conservation areas [Risk Ratio (RR) = 2.47, 95 % confidence interval (CI) 1.0 - 6.06, p = 0.047] and reduced by the presence of recreational areas within the relevant neighbourhood (RR = 0.13, 95 % CI 0.04 - 0.34, p < 0.001). The preceding extreme climate events (extreme heat and extreme precipitation) influenced the rate of canine leptospirosis in opposite ways, with extreme rainfall at lag -13, -10 and -9 weeks significantly increased rate. The re-emergence of canine leptospirosis in southern NSW was multifactorial, with hydrological events likely the main driving factor. Increased pet owner awareness during and following such events is advocated.