First report of a parapoxvirus red deer infection in reindeer (Rangifer tarandus tarandus): clinical presentation and full-genome characterization

In September 2023, five semi-domesticated reindeer calves (Rangifer tarandus tarandus) from Norrbotten County, Sweden, displayed clinical signs resembling contagious ecthyma. Samples were collected from the lesion sites, including the skin of the muzzle, eyelids, and oral mucosa. The samples were analysed via real-time PCR (qPCR) for parapoxviruses (PPV) and cervidpoxviruses (CvPV). Both viruses were detected in samples from several calves. Full genome sequencing of the PPV strain 23-MIK191411 revealed close similarity to the parapoxvirus red deer (RDPV) strain HL953 from a red deer (Cervus elaphus) in Germany but with a novel 2,187 bp insert in the right terminal third of the genome. This insert carried two open reading frames (ORFs) that, while divergent, presented sequence homology with several other PPVs. Analysis of amino acid differences relative to the sequence of the RDPV HL953 strain revealed that proteins implicated in host interactions and virulence presented the greatest differences. Thus, comparative sequence analysis indicates that an RDPV has recombined with an ancestor of 23-MIK191411 and adapted to the reindeer host. This study represents the first detection of RDPV, with a unique insert likely originating from an unknown PPV in reindeer, indicating its emergence beyond the red deer host range. Clinical signs are consistent with those caused by other poxviruses, including CvPV also detected in the investigated animal group, making it difficult to diagnose the causative agent solely via clinical observation. In the sequenced sample, RDPV was confirmed as the predominant variant. These findings underscore the importance of molecular diagnostics for accurate pathogen identification and highlight the need for continued health surveillance of reindeer. Further investigations are needed to determine the clinical impact of RDPV in reindeer.