RARE DISEASE
Herpes simplex virus encephalitis
Herpes simplex virus encephalitis
Herpes simplex virus encephalitis
Synonyms: HSE, HSV encephalitis, HSVE, Herpes simplex meningo-encephalitis, Herpes simplex neuroinvasion, Herpetic encephalitis
Synonyms: HSE, HSV encephalitis, HSVE, Herpes simplex meningo-encephalitis, Herpes simplex neuroinvasion, Herpetic encephalitis
Synonyms: HSE, HSV encephalitis, HSVE, Herpes simplex meningo-encephalitis, Herpes simplex neuroinvasion, Herpetic encephalitis
Drug discovery
2
drugs
With orphan designations
Overview
Herpes simplex virus encephalitis (HSE), primarily caused by HSV-1, is a life-threatening neurologic infection characterized by fever, altered consciousness, seizures, and focal deficits. Prompt IV acyclovir (10 mg/kg every 8 hours for 14–21 days) reduces mortality from 70–80% to 10–20% [2][9]. Adjunct corticosteroids may mitigate inflammation in severe cases [3][13]. Delays in treatment beyond 48 hours increase mortality and neurocognitive sequelae (30–40% survivors) [1][9]. Autoimmune anti-NMDA receptor encephalitis can occur post-HSE [2].
Burden
Mortality: 7.7% in adults, 6.9% in neonates; survivors face epilepsy (38%), cognitive impairment, or behavioral disorders [4][9][12].
Economic burden: Prolonged ICU stays (median 3–14 days) and high rehabilitation needs [1][14].
Global disparities: LMICs face higher morbidity due to delayed diagnostics and treatment barriers [14].
Therapies
First-line: High-dose IV acyclovir (14–21 days), with CSF-PCR monitoring to guide duration [2][11].
Adjunctive therapies: Corticosteroids (e.g., dexamethasone) for fulminant cases to reduce cerebral edema [3][13].
Supportive care: Seizure management, ICP control, and rehabilitation for residual deficits [6][13].
Categories: rare genetic diseases, rare immunological diseases, rare infectious diseases, rare neurological diseases
Research Papers
1,229 drug discovery papers related to Herpes simplex virus encephalitis, with 5 first-in-class and 0 next-in-class early-stage therapies forecasted to outperform the average preclinical success rate. Recent publications:
1,229 drug discovery papers related to Herpes simplex virus encephalitis, with 5 first-in-class and 0 next-in-class early-stage therapies forecasted to outperform the average preclinical success rate. Recent publications:
2026-07-10 | The cell-mediated adaptive immune response to herpes simplex virus type 1 encephalitis: mechanisms and clinical implications
Herpes simplex virus (HSV) encephalitis is the most frequent cause of sporadic encephalitis globally. Despite the emergence of the antiviral drug aciclovir curtailing mortality, this disease remains a clinical challenge due to its rapid progression and associated neurological sequelae; indicating the urgent requirement for adjunctive neuroprotective treatment options. Recent studies using both human samples and murine models have highlighted how cell mediated immune cells including CD8+, CD4+ and brain tissue-resident memory T cells have the capacity to act as a ‘double-edged sword’; both serving to protect the host against HSV encephalitis, but also increasing neuroglial injury by inflammation. Factors which impair cell-mediated immunity may predispose individuals to herpes simplex encephalitis, including defects in viral immune evasion strategies (infected cell protein 47, UL13 kinase), host genetic pre-disposition (toll-like receptor 3 deficiency, lymphotoxin-α deficiency, Rel mutations) and external factors such as stress. Additionally, there is a particular need for clinical vigilance for patients on immunosuppressive treatments which impair cell-mediated immunity, including azathioprine, hydroxychloroquine and methotrexate. Conversely, understanding these molecular mechanisms may provide new insights into the use of immunomodulatory strategies including anakinra, tocilizumab, and the implementation of targeted vaccination. This review summarises the current state of knowledge of how an impaired cell-mediated immune response could promote herpes simplex virus encephalitis, followed by an exploration of the clinical applications and therapeutic interventions which could viably be implemented to ameliorate immune-mediated tissue injury.
2026-07-10 | Structure and mechanism of the HSV-1 origin-binding protein UL9.
The herpesvirus DNA replication machinery comprises a battery of viral enzymes that orchestrate viral genome synthesis. In herpes simplex virus type 1 (HSV-1), the machinery consists of seven essential components, including the origin-binding protein UL9, the single-stranded DNA (ssDNA)-binding protein ICP8, the heterodimeric DNA polymerase complex UL30-UL42, and the heterotrimeric helicase-primase complex UL5-UL8-UL52. UL9, a superfamily 2 (SF2) helicase, functions as a dimer that specifically recognizes replication origins and unwinds duplex DNA to initiate replication. Furthermore, UL9 recruits the replication machinery through interactions with viral components and engages cellular proteins that regulate its function. However, the molecular mechanisms underlying the multifunctionality of UL9 remain incompletely understood due to the lack of structural information. Here, we present cryo-electron microscopy structures of UL9 in both apo and DNA-bound states. Together with biochemical and enzymatic assays, we elucidate the molecular basis of UL9 dimerization, origin recognition and allosteric regulation by ICP8.IMPORTANCEHerpes simplex virus 1 (HSV-1) is a widespread virus that causes lifelong infections, leading to periodic outbreaks ranging from common cold sores to life-threatening encephalitis, and no current treatment can eradicate the dormant virus. To multiply, HSV-1 relies on a protein-based molecular machine to replicate its genome, where the unwinding of double-stranded DNA at specific replication origins is coordinated by the viral origin-binding protein UL9. Here, we present the high-resolution structures of UL9, both alone and bound to DNA, revealing how it forms a stable homodimer to grab onto the origin. Combined with precise biochemical experiments, we further show how UL9 collaborates with another viral helper protein, ICP8, to unwind DNA efficiently. These discoveries solve a long-standing puzzle in herpesvirus biology and offer a vital structural blueprint for designing new antiviral drugs that can block viral replication at its very earliest stage.
2026-07-09 | Glycoprotein G enables HSV-2 neuroinvasion and provides protection as a glycosylated vaccine antigen.
The role of glycoprotein G (gG-2) of herpes simplex virus type 2 (HSV-2) in viral pathogenesis remains poorly understood. gG-2 is cleaved into a secreted form (sgG-2) and a membrane-associated form (mgG-2), but the in vivo function of mgG-2 and the contribution of its glycosylation to immune responses have not been defined. Here, we provide a comprehensive characterization of the N- and O-linked glycosylation profile of mgG-2 and investigate its functional relevance for viral spread and vaccine-induced immunity. Using a mouse genital infection model, we show that an mgG-2-deficient HSV-2 mutant replicates in vaginal epithelial cells but is severely impaired in dissemination to dorsal root ganglia and the central nervous system, identifying mgG-2 as a key determinant of neuronal spread in vivo. In parallel, immunization with recombinant mgG-2 elicited strong humoral and Th1-polarized CD4 + T-cell responses and conferred protection against genital HSV-2 challenge. Importantly, glycosylation of mgG-2 was required for optimal immunogenicity and protection, as deglycosylated variants induced reduced CD4 + T-cell responses and allowed increased viral spread to neuronal tissues. Mechanistically, our findings suggest that glycosylation of mgG-2 modulates antigen recognition and shapes adaptive immune responses that limit viral dissemination after vaccination. Together, these results demonstrate that mgG-2 plays a critical role in HSV-2 pathogenesis and provide a strong rationale for targeting glycosylated mgG-2 in the development of both prophylactic and therapeutic vaccines against HSV-2.
2026-07-10 | The cell-mediated adaptive immune response to herpes simplex virus type 1 encephalitis: mechanisms and clinical implications
Herpes simplex virus (HSV) encephalitis is the most frequent cause of sporadic encephalitis globally. Despite the emergence of the antiviral drug aciclovir curtailing mortality, this disease remains a clinical challenge due to its rapid progression and associated neurological sequelae; indicating the urgent requirement for adjunctive neuroprotective treatment options. Recent studies using both human samples and murine models have highlighted how cell mediated immune cells including CD8+, CD4+ and brain tissue-resident memory T cells have the capacity to act as a ‘double-edged sword’; both serving to protect the host against HSV encephalitis, but also increasing neuroglial injury by inflammation. Factors which impair cell-mediated immunity may predispose individuals to herpes simplex encephalitis, including defects in viral immune evasion strategies (infected cell protein 47, UL13 kinase), host genetic pre-disposition (toll-like receptor 3 deficiency, lymphotoxin-α deficiency, Rel mutations) and external factors such as stress. Additionally, there is a particular need for clinical vigilance for patients on immunosuppressive treatments which impair cell-mediated immunity, including azathioprine, hydroxychloroquine and methotrexate. Conversely, understanding these molecular mechanisms may provide new insights into the use of immunomodulatory strategies including anakinra, tocilizumab, and the implementation of targeted vaccination. This review summarises the current state of knowledge of how an impaired cell-mediated immune response could promote herpes simplex virus encephalitis, followed by an exploration of the clinical applications and therapeutic interventions which could viably be implemented to ameliorate immune-mediated tissue injury.
2026-07-10 | Structure and mechanism of the HSV-1 origin-binding protein UL9.
The herpesvirus DNA replication machinery comprises a battery of viral enzymes that orchestrate viral genome synthesis. In herpes simplex virus type 1 (HSV-1), the machinery consists of seven essential components, including the origin-binding protein UL9, the single-stranded DNA (ssDNA)-binding protein ICP8, the heterodimeric DNA polymerase complex UL30-UL42, and the heterotrimeric helicase-primase complex UL5-UL8-UL52. UL9, a superfamily 2 (SF2) helicase, functions as a dimer that specifically recognizes replication origins and unwinds duplex DNA to initiate replication. Furthermore, UL9 recruits the replication machinery through interactions with viral components and engages cellular proteins that regulate its function. However, the molecular mechanisms underlying the multifunctionality of UL9 remain incompletely understood due to the lack of structural information. Here, we present cryo-electron microscopy structures of UL9 in both apo and DNA-bound states. Together with biochemical and enzymatic assays, we elucidate the molecular basis of UL9 dimerization, origin recognition and allosteric regulation by ICP8.IMPORTANCEHerpes simplex virus 1 (HSV-1) is a widespread virus that causes lifelong infections, leading to periodic outbreaks ranging from common cold sores to life-threatening encephalitis, and no current treatment can eradicate the dormant virus. To multiply, HSV-1 relies on a protein-based molecular machine to replicate its genome, where the unwinding of double-stranded DNA at specific replication origins is coordinated by the viral origin-binding protein UL9. Here, we present the high-resolution structures of UL9, both alone and bound to DNA, revealing how it forms a stable homodimer to grab onto the origin. Combined with precise biochemical experiments, we further show how UL9 collaborates with another viral helper protein, ICP8, to unwind DNA efficiently. These discoveries solve a long-standing puzzle in herpesvirus biology and offer a vital structural blueprint for designing new antiviral drugs that can block viral replication at its very earliest stage.
2026-07-09 | Glycoprotein G enables HSV-2 neuroinvasion and provides protection as a glycosylated vaccine antigen.
The role of glycoprotein G (gG-2) of herpes simplex virus type 2 (HSV-2) in viral pathogenesis remains poorly understood. gG-2 is cleaved into a secreted form (sgG-2) and a membrane-associated form (mgG-2), but the in vivo function of mgG-2 and the contribution of its glycosylation to immune responses have not been defined. Here, we provide a comprehensive characterization of the N- and O-linked glycosylation profile of mgG-2 and investigate its functional relevance for viral spread and vaccine-induced immunity. Using a mouse genital infection model, we show that an mgG-2-deficient HSV-2 mutant replicates in vaginal epithelial cells but is severely impaired in dissemination to dorsal root ganglia and the central nervous system, identifying mgG-2 as a key determinant of neuronal spread in vivo. In parallel, immunization with recombinant mgG-2 elicited strong humoral and Th1-polarized CD4 + T-cell responses and conferred protection against genital HSV-2 challenge. Importantly, glycosylation of mgG-2 was required for optimal immunogenicity and protection, as deglycosylated variants induced reduced CD4 + T-cell responses and allowed increased viral spread to neuronal tissues. Mechanistically, our findings suggest that glycosylation of mgG-2 modulates antigen recognition and shapes adaptive immune responses that limit viral dissemination after vaccination. Together, these results demonstrate that mgG-2 plays a critical role in HSV-2 pathogenesis and provide a strong rationale for targeting glycosylated mgG-2 in the development of both prophylactic and therapeutic vaccines against HSV-2.
Access all drug discovery articles and probability of success in trials forecasts:
Access all drug discovery articles and probability of success in trials forecasts:
Drug Discovery Landscape
2 orphan drug designations for Herpes simplex virus encephalitis.
2 orphan drug designations for Herpes simplex virus encephalitis.
Drug | Therapy type | Regulator | Orphan designation | Approval | Sponsor |
|---|---|---|---|---|---|
granzyme B associated peptide | peptides | FDA | 2025-06-25 | — | BioJENC, LLC. |
PR-225 (redox-acyclovir) | small molecules | FDA | 1990-05-29 | — | Pharmos |
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