Herpes simplex virus encephalitis

Herpes simplex virus encephalitis (HSE), also known as herpes simplex encephalitis or herpetic encephalitis, is a severe and life-threatening infection of the brain caused by herpes simplex virus (HSV), most commonly HSV type 1 (HSV-1) in older children and adults, and HSV type 2 (HSV-2) in neonates. It is the most common cause of sporadic fatal viral encephalitis worldwide. The virus primarily affects the central nervous system, with a particular predilection for the temporal and frontal lobes of the brain, leading to necrotizing and hemorrhagic inflammation. Key symptoms typically develop acutely or subacutely over days and include high fever, headache, altered consciousness, confusion, behavioral changes, seizures, focal neurological deficits (such as hemiparesis or aphasia), and memory impairment. Without treatment, the disease progresses rapidly to coma and death in the majority of cases. Neonatal HSE may present as part of disseminated herpes infection or as isolated central nervous system disease, often with lethargy, seizures, and poor feeding. Susceptibility to HSE in some individuals has been linked to inborn errors of immunity, particularly defects in the Toll-like receptor 3 (TLR3) signaling pathway and interferon production, including mutations in genes such as TLR3, UNC93B1, TRAF3, TBK1, IRF3, and STAT1. These genetic predispositions follow various inheritance patterns (autosomal dominant or autosomal recessive depending on the gene involved) and are particularly relevant in childhood-onset HSE. Early diagnosis through PCR detection of HSV DNA in cerebrospinal fluid and brain MRI is critical. The standard treatment is intravenous acyclovir, which has dramatically reduced mortality from approximately 70% to around 20%, though significant neurological sequelae remain common among survivors, including memory deficits, cognitive impairment, and behavioral changes. Prompt initiation of antiviral therapy is essential for improved outcomes.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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