Pathogenic characterization and genome-wide evolutionary analysis of Bacillus anthracis from a cutaneous anthrax case in Inner Mongolia, China

BACKGROUND: Anthrax remains an important zoonosis in pastoral areas of China, yet genomic evidence directly linking human cases, contaminated animal products, and environmental sources is still limited for Hinggan League in Inner Mongolia. We investigated a cutaneous anthrax event reported in 2023 and characterized the associated Bacillus anthracis isolates using epidemiological and genome-based approaches. METHODS: A field investigation was initiated after a suspected case was reported on 2 November 2023. Eighteen samples were collected from the patient, residual products from the slaughtered sheep, and the local environment. Bacillus anthracis was detected by real-time PCR and isolated by culture with phenotypic confirmation. Four isolates underwent canSNP typing, short-read whole-genome sequencing, average nucleotide identity (ANI) analysis, and core-genome multilocus sequence typing (cgMLST) against a contextual public genome dataset. RESULTS: One confirmed case of cutaneous anthrax was identified after the patient slaughtered and skinned a moribund sheep. Four of 18 samples were PCR-positive, and four Bacillus anthracis isolates were recovered from the patient, mutton, sheepskin, and a transport vehicle. All four isolates belonged to the A.Br.001/002 lineage and showed very high genome-wide similarity. Combined epidemiological and cgMLST evidence supported a single-source event linking the infected sheep, contaminated animal products, the transport environment, and the human case. CONCLUSIONS: This study documents a localized zoonotic anthrax outbreak associated with the slaughter of an infected sheep and demonstrates the value of integrating routine microbiological investigation with genome-based typing for source tracing in pastoral settings.