HSV Encephalitis in Adults

• In adults, herpes simplex virus type 1 (HSV-1) accounts for 95% of all fatal cases of sporadic encephalitis and usually results from reactivation of the latent virus.
• An isolated case report of an immunocompromised adult patient developing HSV-2 infection has been described.
• Adult HSV-1 encephalitis often results from reactivation of latent HSV in the trigeminal ganglion. The virus spreads along the orbitofrontal and temporal meningeal branches of this cranial nerve and then to the anterior and middle cranial fossa. Atypical spread can occur when cranial nerves IX and X are involved. 
• The virus has a predilection for the limbic system, involving one or both temporal lobes, and often involving the hippocampus, parahippocampus, and amygdala. Frontal and parietal spread also can occur.