Treponema phagedenis in bovine digital dermatitis: biology, pathogenesis, immunity, and control strategies: a narrative review.

Treponema phagedenis is one of the major treponemal species associated with bovine digital dermatitis (BDD), a contagious infectious hoof disease that causes lameness, reduced productivity, impaired animal welfare, and substantial economic losses in dairy and beef cattle worldwide. Since BDD was first described in 1974, the disease has been reported in many cattle-producing countries, and molecular studies have consistently identified BDD-associated Treponema species, including T. phagedenis, T. medium, and T. pedis, in active lesions. However, BDD is a polymicrobial disease, and the precise role of T. phagedenis as a primary pathogen, opportunistic colonizer, or contributor to lesion persistence remains incompletely resolved. This review summarizes current knowledge of the biological characteristics, global epidemiology, host range, pathogenic mechanisms, immune responses, diagnostic approaches, and prevention and control strategies related to T. phagedenis. Particular attention is given to culture requirements, lesion-stage progression, immune modulation, antigenic variation, candidate vaccine antigens, and recurrence after treatment. Current evidence suggests that T. phagedenis may contribute to chronic inflammation and lesion recurrence through tissue-associated persistence, host immune modulation, and interactions with other lesion-associated microorganisms. In China, systematic epidemiological data and confirmed local isolates remain limited, which restricts strain-level characterization and evidence-based control. Future studies should integrate culture-based isolation, molecular surveillance, comparative genomics, transcriptomics, proteomics, antimicrobial susceptibility testing, and vaccine-oriented antigen validation to clarify the role of T. phagedenis in BDD and improve disease prevention.