Bell's palsy and lip HSV-1 infection: importance of subcutaneous access.

Although HSV-1 has been implicated in facial palsy for a long time, testing and treating for HSV is not routine. The lack of a meaningful demonstration of how HSV-1 would cause facial palsy has limited progress in this field. Herein we demonstrate that the depth of the lip HSV-1 infection defines the course of the disease, with deeper subcutaneous infection allowing virus access to the facial nerve and causing facial palsy. HSV-1 inoculated subcutaneously caused extensive facial paralysis in cotton rats , while virus inoculated in the same area of the lip by skin surface abrasion did not. Demyelination along the facial nerve (CN VII) accompanied subcutaneous HSV-1 infection and was identified as the possible underlying mechanism of the disease. This causality demonstration is particularly important in light of increased facial palsy outbreaks associated with SARS-CoV-2 infection and SARS-CoV-2 and influenza vaccinations.