HSV
One-Sentence Definition
Herpes simplex viruses (HSV-1 and HSV-2) are enveloped double-stranded DNA herpesviruses that cause oral/genital lesions and severe disease (encephalitis, neonatal herpes), establishing lifelong latency in sensory ganglia with periodic reactivation.
Taxonomy & Structure
- Family Herpesviridae, subfamily Alphaherpesvirinae
- Linear dsDNA; icosahedral capsid; tegument; lipid envelope with glycoproteins (gB, gD…)
- HSV-1 traditionally oral/encephalitis; HSV-2 traditionally genital — substantial overlap epidemiologically
Replication & Pathogenesis Highlights
- Lytic replication in epithelium → retrograde transport to ganglia → latency (episomal DNA, latency-associated transcripts)
- Reactivation → anterograde return to mucosa/skin (triggers: stress, UV, immunosuppression)
- Immune evasion and neuronal sanctuary sites prevent sterilizing clearance
- Contrast with VZV/CMV/EBV — same family, different niches (expand later)
Clinical Syndromes
- Orolabial herpes; genital herpes; herpetic whitlow; eczema herpeticum
- HSV encephalitis (often temporal lobe; HSV-1) — neurologic emergency
- Keratitis → vision threat
- Neonatal herpes (SEM, CNS, disseminated) — perinatal transmission
- Severe disease in immunocompromised hosts
Diagnosis
- PCR / qPCR of lesion swab, CSF (encephalitis), blood (neonatal/disseminated) — method of choice
- Tzanck smear / culture historically; serology for past exposure (type-specific IgG) not for acute CNS decisions
- DNA Extraction from CSF/swabs; multiplex meningitis/encephalitis panels (Syndromic Molecular Panels)
Treatment Notes (conceptual)
- Acyclovir / valacyclovir / famciclovir — thymidine kinase–dependent activation
- IV acyclovir for encephalitis and neonatal disease
- Resistance (TK or polymerase mutations) in immunocompromised — foscarnet/cidofovir territory
- Suppression therapy for frequent genital recurrences; no cure for latency
Genomics & Computational Notes
- Resistance genotyping of UL23 (TK) / UL30 (pol)
- CSF PCR quantification sometimes used; presence matters more than titer for encephalitis diagnosis
- Not typically WGS’d for routine care; outbreak typing rare vs respiratory viruses
Related Notes
- Vaccination (no routine HSV vaccine yet) · Infection Prevention and Control · PCR
- MOCs: MOC - Virology · MOC - Diseases by System · MOC - Immunology · CNS Infections
Active Recall
- Where does HSV establish latency?
- First-line drug class and activation requirement?
- Preferred test for suspected HSV encephalitis?