Leptospirosis is an emerging infectious disease of pig-hunting dogs and humans in north Queensland

Background Leptospirosis is a zoonotic disease with a worldwide distribution, caused by pathogenic serovars in the genus Leptospira. Feral pigs are known carriers of Leptospira species and pig hunting using dogs is a common recreational activity in Queensland, Australia. Methodology and principal findings This study aimed to determine the seroprevalence of Leptospira spp. serovars in pig-hunting dogs above the Tropic of Capricorn in Queensland and by establishing the geographic distribution, serovars and incidence of human cases of leptospirosis in Queensland, identify potential overlap between human and canine exposure. We also explored the knowledge and risk-taking behaviours of pig-hunting dog owners towards zoonotic diseases. Ninety-eight pig-hunting dogs deemed healthy by physical examination and owned by 41 people from Queensland had serum submitted for Microscopic Agglutination Testing (MAT) to determine antibody titres against Leptospira serovars, while 40/41 dog owners completed a survey on their knowledge of diseases relating to pig hunting. Human leptospirosis cases (n = 330) notified to Queensland Health between 2015-2018 were analysed. Approximately one quarter (23/87; 26%) of unvaccinated pig-hunting dogs were seropositive to Leptospira spp. Although harder to interpret, 8/11 (73%) vaccinated dogs were seropositive to Leptospira spp. Pig hunters may be more likely to contract leptospirosis compared with the general Queensland population, based on responses from surveyed hunters. The highest concentration of human leptospirosis was in the wet tropics region of Far North Queensland. There was little overlap between the serovars dogs were exposed to and those infecting humans. The dominant serovar identified in unvaccinated dogs was Australis (13/23; 57%), with serovar Arborea (36/330; 10.9%) responsible for the highest number of human leptospirosis cases. Topaz was the second most common serovar in both humans and dogs and was previously unrecorded in Australian dogs. Most hunters surveyed used hand washing as a zoonotic disease risk reduction technique. Conclusions Leptospirosis is an emerging disease of growing significance. The infection requires a 'one health' approach to understand its epidemiology. With shifting climatic patterns influencing human-animal-environment interactions, ongoing monitoring of diseases like leptospirosis is critical to helping prevent infection of individuals and disease outbreaks. Author summary Leptospirosis is a disease caused by pathogenic Leptospira serovars. Leptospira can infect both humans and animals depending on the species and serovar, with disease resulting from direct or indirect exposure to infected urine. In Australia, the highest number of human cases recorded annually occur in the state of Queensland. Feral pig hunting is a popular recreational activity in this state and hunters often use dogs to 'flush out' pigs. This study investigated whether dogs used to hunt feral pigs were exposed to Leptospira serovars, the geographic distribution of human leptospirosis cases and canine exposure to Leptospira serovars in Queensland, and the knowledge of this disease amongst owners of pig-hunting dogs. We found that roughly one quarter of unvaccinated pig-hunting dogs had been exposed to Leptospira spp. The wet tropics region of Far North Queensland was found to be the location of highest risk for exposure to Leptospira for humans. There was little overlap between the serovars dogs had been exposed to and those reported to have caused disease in humans, except for the serovars Topaz, Australis, and Pomona. Finally, pig hunters were found to be at increased risk of being diagnosed with leptospirosis compared to the Queensland public and engaged in risky hunting practices such as not wearing personal protective equipment (PPE). Our findings reinforce the emerging significance of leptospirosis for physicians and veterinarians in Australia.