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 immune-compromised 63-year-old man reported testicular pain with postmortem detection of viral antigen in the testes suggested 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 log ₁₀ PFU/gram tissue in testes. Furthermore, we find that at 5dpi 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 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.