Buruli ulcer surveillance in south-eastern Australian possums: Infection status, lesion mapping and internal distribution of Mycobacterium ulcerans

Buruli ulcer (BU) is a neglected tropical disease of skin and subcutaneous tissues caused by Mycobacterium ulcerans. BU-endemic areas are highly focal, and M. ulcerans transmission dynamics vary by setting. In Victoria, Australia, BU is an endemic vector-borne zoonosis, with mosquitoes and native possums implicated in transmission, and humans incidental hosts. Despite the importance of possums as wildlife reservoirs of M. ulcerans, knowledge of BU in these animals is limited. Opportunistic necropsy-based and active trap-and-release surveillance studies were conducted across Melbourne and Geelong, Victoria, to investigate BU in possums. Demographic data and biological samples were collected, and cutaneous lesions suggestive of BU were mapped. Samples were tested for the presence of M. ulcerans DNA by IS2404 qPCR. The final dataset included 26 possums: 20 necropsied; 6 trapped and released. Most possums (77%) were common ringtails from inner Melbourne. Nine had ulcers, ranging from single and mild, to multiple and severe, exposing bones and tendons in three cases. M. ulcerans was confirmed in 73% (19/26) of examined possums: 8 with lesions and 11 without. Oral swabs were most frequently indicative of M. ulcerans infection status. Severely ulcerated possums had widespread systemic internal bacterial dissemination and were shedding M. ulcerans in faeces. The anatomical distribution of ulcers and PCR positivity of biological samples suggests possums may contract BU from bites of M. ulcerans-harbouring mosquitoes, traumatic skin wounds, ingestion of an unknown environmental source, and/or during early development in the pouch. Ringtail possums appear highly susceptible to infection with M. ulcerans and are important bacterial reservoirs in Victoria. Oral swabs should be considered for diagnosis or surveillance of infected possums. A One Health approach is needed to design and implement integrated interventions that reduce M. ulcerans transmission in Victoria, thereby protecting wildlife and humans from this emerging zoonotic disease.