Facial nerve paralysis induced by herpes simplex virus in mice: an animal model of acute and transient facial paralysis.

We have been the first to succeed in producing an acute and transient facial paralysis simulating Bell's palsy, by inoculating herpes simplex virus into the auricles or tongues of mice. The KOS strain of the virus was injected into the auricle of 104 mice and the anterior two thirds of the tongue in 30 mice. Facial paralysis developed between 6 and 9 days after virus inoculation, continued for 3 to 7 days, and then recovered spontaneously. The animals were painlessly sacrificed between 6 and 20 days after inoculation for histopathologic and immunocytochemical study. Histopathologically, severe nerve swelling, inflammatory cell infiltration, and vacuolar degeneration were manifested in the affected facial nerve and nuclei. Herpes simplex virus antigens were also detected in the facial nerve, geniculate ganglion, and facial nerve nucleus. The pathophysiologic mechanisms of the facial paralysis are discussed in light of the histopathologic findings, in association with the causation of Bell's palsy.