Herpes simplex virus and central nervous system infections: encephalitis, meningitis, myelitis

Central nervous system (CNS) infections caused by herpes simplex viruses 1 (HSV-1) and 2 (HSV-2) greatly vary in frequency and severity. HSV-1 causes mostly herpes simplex encephalitis (HSE) which represents 5% to 15% of infectious encephalitis in children and adults. Despite available molecular diagnosis tools and antiviral drugs, the prognosis of HSE remains unacceptably low. In addition to mortality and immediate sequelae, auto-immune encephalitis (AIE) may occur, associated with the development of anti-neuronal antibodies in 1/4 of cases. Replicative relapses have been associated in few cases with genetic defects altering the innate immune response of neuronal cells. Herpetic meningitis is frequent, mostly associated with HSV-2 and genital herpes, sometimes recurrent and, mostly benign, except in immunocompromised individuals. Finally, exceptional cases of myelitis have been reported, due to ascending propagation of HSV-2 in the CNS. This review does not include neonatal infections.