Severe cases of Buruli ulcer (infection with Mycobacterium ulcerans) in common ringtail possums in Victoria adversely affect animal welfare

Abstract

Buruli ulcer is a chronic ulcerative disease of the skin and subcutaneous tissues caused by infection with Mycobacterium ulcerans. Although Australian possums are known to be susceptible to Buruli ulcer, many aspects of the disease in possums, including welfare impacts, remain largely unreported. Severe clinical Buruli ulcer was identified in four common ringtail possums (Pseudocheirus peregrinus) from Melbourne, Victoria. All four possums were euthanased due to the presence of deep ulcerative lesions on paws, with extensive tissue necrosis that exposed bones and tendons in three cases. Histologically, there was severe ulcerative necrotising pyogranulomatous dermatitis, panniculitis and myositis, with intralesional acid-fast bacteria. M. ulcerans was detected by real-time PCR in all swabs, tissues and faeces collected from all four cases. Buruli ulcer may be an important and under-recognised cause of poor possum welfare in endemic areas. The physical impacts of the severe cutaneous lesions, especially those extending to underlying bones and joints, would have directly impaired the mobility of these possums, affecting navigation of their natural environments and expression of natural behaviours including foraging and socialising. Systemic distribution of M. ulcerans throughout all major internal organs, as observed here, may further impact the health and fitness of infected possums. Faecal shedding of M. ulcerans in all four cases supports the role of possums as zoonotic reservoirs. Further research is needed to investigate the epidemiology, pathogenesis and welfare impacts of Buruli ulcer in possums and to inform the design of interventions that may protect their health and welfare.