Zoonotic transmission of diphtheria toxin‐producing Corynebacterium ulcerans

Background Diphtheria caused by toxin‐producing Corynebacterium ulcerans is a re‐emerging human disease that can cause local and systemic sequelae. In Australia, toxigenic diphtheria is a rare notifiable communicable disease, due to high‐vaccination coverage. The public health management of cutaneous cases of toxigenic C. ulcerans varies between jurisdictions, as opposed to the more uniform public health response to toxigenic Corynebacterium diphtheriae presenting as respiratory or laryngeal diphtheria. Aim To report a case of zoonotically acquired C. ulcerans, review evidence on the zoonotic reservoir and reported transmission events, and examine public health guidelines for the management of human and animal contacts. Methods and Results In this case report, we detail our case investigation, treatment and public health management, including contact tracing and an approach to animal testing. We successfully identified companion canines as probable sources for the human case, with WGS confirming the link. The zoonotic disease link of C. ulcerans to domestic and agricultural animals is established in the literature; however, the management of animal contacts in human cases is inconsistent with jurisdictional or national guidelines. Conclusions While a rare disease, a consistent approach to public health management is warranted to systematically elucidate the disease source and improve understanding of transmission.