Serovar Australis replaces serovar Copenhageni as the most common cause of canine leptospirosis in New South Wales, Australia.

Highly fatal canine leptospirosis emerged in urban Sydney dogs in 2017, and serovar Copenhageni, against which a registered monovalent vaccine is available, was predominant until 2020. This study was conducted to (1) determine serological characteristics of canine leptospirosis in New South Wales (NSW) between 2021 and 2023; (2) describe the geospatial distribution of leptospirosis; and (3) evaluate if clinicopathological abnormalities and outcome differ between the dominant infecting serovars, Copenhageni versus Australis. Cases were identified through referral or direct veterinarian contact and included if clinical and clinicopathological findings confirmed leptospirosis. Between 2021 and 2023 leptospirosis was confirmed in 61 dogs in NSW. In 2022 two major outbreaks occurred in the local government areas of Shoalhaven (n = 23) and Lake Macquarie (n = 7). The most common serovar identified by microscopic agglutination test (MAT) was Australis (n = 23) followed by Copenhageni (n = 8), Pomona (n = 2), Robinsoni (n = 2) and Bratislava (n = 1). In 16/18 cases from Shoalhaven in which serological results were available, serovar Australis was identified. Dogs infected with serovar Copenhageni were significantly (P < 0.05) more likely to have hepatic involvement with significantly higher liver enzyme activities, bilirubin concentration and icterus, whereas dogs with serovar Australis were significantly (P < 0.01) more likely to have glucosuria. Overall case fatality rate was 40% and was not different between infecting serovars. There are regional differences of infecting serovars with distinct leptospirosis hotspots, and differences in clinicopathological findings. The apparent emergence of serovar Australis highlights the need for bi- or multivalent vaccines and ongoing case surveillance of causal serovars is needed. Glucosuria should prompt leptospirosis testing in endemic areas.