Powassan Virus Infects Mouse Testes and Reveals a Protective Role for Phagocytic Cells

Powassan virus (POWV) is an emerging tick-borne orthoflavivirus with consistently increasing annual prevalence. Though understood as a vector-transmitted virus associated with neurological disease, a 2016 fatal case of an immunocompromised 63-year-old man reported testicular pain with postmortem detection of viral antigen in the testes, suggesting an altered tropism. The extent to which POWV can infect testes remains unclear. We used a BALB/c mouse model of POWV to elucidate the potential of POWV to establish infection in testes and model a potential mechanism of testicular tropism. Here, we report that POWV productively infects the male reproductive tract of mice. We find that POWV consistently infects mouse testes and epididymides at 3 and 5 days post-infection (dpi) with peak titers measuring 6.1 log₁₀ PFU/gram of tissue in testes. Furthermore, we find that at 5 dpi, POWV-infected mice testes are significantly higher in mass than uninfected controls. Due to macrophages being implicated in driving testicular pathogenesis in Zika virus, a related orthoflavivirus, we depleted phagocytic cells using clodronate liposomes prior to POWV infection and compared them to control liposome-treated mice. Depletion of phagocytic cells was associated with higher and sustained viremia and significantly higher viral organ burden in the male reproductive tract of mice. Gene expression analysis revealed a robust antiviral, inflammatory, and chemokine response in the testes that was further amplified following phagocytic-cell depletion. These findings implicate the male reproductive tract as a previously underrecognized target of POWV disease and identify phagocytic cells as key in limiting viral infection of testes in mice.