Emerging human and canine leptospirosis in New South Wales: insights from a One Health geospatial study

After an apparent absence of disease, 79 cases of canine leptospirosis were reported in New South Wales (NSW), Australia between 2017 and 2023. Between 2016 and 2023, 281 human leptospirosis cases were reported in NSW. Our aim was to compare the geospatial distribution and causative serovars of canine and human cases to investigate if cases are possibly associated.

Human data (n = 190) included Statistical Area Level 3 (SA3)-location, place of acquisition, and serovar; cases acquired outside NSW were excluded. Canine data comprised postcodes (allocated to corresponding SA3) and serovar. Spatial patterns for human and canine cases were mapped, and correlations between human and canine cases were examined.

In dogs, serovar Australis (n = 23, 29 %) and Copenhageni (n = 14, 18 %) were most common, whereas in humans it was serovar Arborea (n = 111, 58 %) and Hardjo (n = 13, 7 %). Serovars causing disease in both humans and dogs were Australis, Copenhageni, Hardjo, Pomona, and Robinsoni. In southeastern NSW, serovar Australis infections increased in both dogs and humans. Canine cases were significantly clustered in Greater Sydney and the South Coast whereas human cases were mainly centered around the North Coast with no significant clustering. Overall, there were nine SA3s where both canine (n = 38) and human (n = 51) cases were reported. There was no evidence of correlation between numbers of human and canine cases at the SA3 level (Spearman's rank correlation coefficient [r] = -0.053, P = 0.641) and no overlap between specific serovars at the spatial level.

Our results do not support dog-human transmission or common sources of infection.