The silent spread: uncovering the diversity and evolution of poxviruses in ticks across Western China’s host landscapes

Poxviruses are a diverse group of pathogens with significant implications for both human and animal health. Ticks, as hematophagous arthropods, are capable of switching hosts during their life cycle. Although previous research has suggested the potential for parapoxviral transmission via ticks, the poxviral transmission dynamics remain poorly understood, particularly regarding the role of ticks as vectors. Tick samples were collected from western China, followed by metagenomic sequencing. The diversity of potential blood-feeding hosts and the prevalence of poxviruses were assessed using BWA. Poxviral sequences were assembled using MetaSPAdes and TGICL, and phylogenetic analysis was conducted to examine the origin of prevalent poxviruses and the unblasted poxviral fragments in ticks. A total of 61 poxvirus species across 22 genera were identified, with 387 distinct poxviral sequences assembled. Of these, viral and host abundance were relatively higher in Tibet than in samples from Shaanxi and Gansu. Notably, unblasted gene fragments were identified within the assembled poxviral genomes, originating from a broad range of hosts, including mammals (e.g., rodents), fish, and arthropods. Phylogenetic analysis of the parapoxviruses revealed ongoing mutations, particularly in the Parapoxvirus orf, suggesting an increase in adaptability and potential pathogenicity. The results indicate that environmental factors such as altitude, host availability and host sensitivity may significantly shape viral diversity and transmission dynamics. Ticks may contribute to the ecological circulation of poxviruses by switching hosts during their life cycle, potentially influencing viral genetic diversity. It underscores the risks of zoonotic spillover, particularly in regions with frequent human-animal interactions.