Simplexviruses

Simplexviruses are a genus of enveloped, double-stranded DNA viruses in the family Herpesviridae, subfamily Alphaherpesvirinae. The genus includes two well-known human pathogens, herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2). These viruses establish lifelong latent infections in sensory ganglia and can reactivate periodically, causing recurrent disease.

The virions are icosahedral, enveloped particles with a linear double-stranded DNA genome of about 150 kilobases. The genome encodes numerous genes organized into immediate-early, early, and late classes that control replication and immune evasion. Replication occurs in the nucleus and follows the characteristic herpesvirus replication strategy, including genome concatemer processing and cytopathic effects in infected cells.

Clinically, HSV-1 is commonly associated with orolabial herpes and can cause keratitis and, rarely, encephalitis. HSV-2 is primarily linked to genital herpes but can also involve extragenital sites and meningitis. Both viruses can be transmitted through direct contact with mucocutaneous lesions or via asymptomatic shedding, and neonatal herpes can occur if infection arises during birth.

Latency and reactivation are central features: after a primary infection, the virus becomes latent in sensory ganglia (trigeminal ganglia for HSV-1; sacral ganglia for HSV-2) and can reactivate, producing recurrent lesions and intermittent viral shedding.

Diagnosis relies on PCR testing of lesion swabs, viral culture, and, in selected cases, serology. Treatment uses nucleoside analogs such as acyclovir, valacyclovir, or famciclovir to reduce severity, duration, and recurrence, but there is no cure. No licensed vaccine exists, though development and testing of candidates continue.