An atypical case of infection with the Mpox virus clade IIb lineage C.1 - clinical and virological findings.

We describe an atypical case of mpox virus (MPXV) infection in a Polish patient, with a focus on clinical presentation, virological characterisation, and the phylogenetic placement of the viral isolate within the emerging C.1 lineage of Clade IIb. The report aims to contribute to a better understanding of MPXV lineage-specific disease features and viral evolution in non-endemic settings. The patient presented with numerous localised lesions and minimal systemic symptoms. Genomic analysis confirmed infection with an MPXV C.1 lineage of Clade IIb responsible for the 2022-2025 global outbreaks. Infection with C.1 lineage may lead to atypical presentations, particularly in immunocompetent individuals. Continued genomic surveillance and clade-specific clinical correlation are essential for accurate diagnosis, risk stratification, and public health response.