Question
Herpes simplex virus 1 ( HSV1 )
Answer
Herpes Simplex Virus type 1 (HSV-1) is a large, enveloped, double-stranded DNA virus (family Herpesviridae), classically associated with oro-facial/orolabial infection (though genital infection with HSV-1 is increasingly recognized, particularly via oro-genital contact), and, like all herpesviruses, establishes lifelong latent infection after primary infection.
Transmission: direct contact with infected oral secretions/lesions (saliva, kissing, shared utensils), typically acquired in childhood.
Pathogenesis and latency: primary infection occurs at the oral/oropharyngeal mucosa; the virus then travels along sensory nerve fibres to establish lifelong latency in the trigeminal ganglion, from which periodic reactivation (triggered by stress, fever, UV exposure, immunosuppression, menstruation) causes recurrent lesions (“cold sores”/fever blisters) at or near the original site, along the distribution of the sensory nerve.
Clinical features:
- Primary infection — often asymptomatic or mild; can present as acute herpetic gingivostomatitis in young children (painful oral vesicles/ulcers, fever, lymphadenopathy).
- Recurrent infection — herpes labialis (cold sores), typically at the vermilion border of the lip, preceded by a prodrome of tingling/burning.
- Other manifestations: herpetic whitlow (finger infection, an occupational risk for healthcare workers); herpes gladiatorum (skin infection from close contact sports); HSV keratitis (a leading infectious cause of corneal blindness in some regions); HSV encephalitis — a serious, potentially fatal complication, classically causing haemorrhagic necrotizing encephalitis with a predilection for the temporal lobes.
Laboratory diagnosis: viral culture (cytopathic effect — multinucleated giant cells) from vesicle fluid; Tzanck smear — cytological examination of vesicle base scraping showing multinucleated giant cells with characteristic intranuclear inclusions (Cowdry type A bodies), a rapid but non-specific test (cannot distinguish HSV from VZV); direct fluorescent antibody test; PCR — the most sensitive method, particularly important for CSF testing in suspected HSV encephalitis, where it has become the diagnostic gold standard.
Treatment: acyclovir (or valacyclovir/famciclovir) — for symptomatic recurrent disease, and, critically, high-dose intravenous acyclovir started empirically without delay in suspected HSV encephalitis, given the high mortality/morbidity of untreated disease and the relative safety of early empirical treatment while awaiting confirmatory PCR.