Viral meningitis and encephalitis

Viruses are a major cause of central nervous system (CNS) infection worldwide. Meningitis and encephalitis commonly present with headache and fever. Encephalitis also causes neurological deficits, reflecting the involvement of the brain parenchyma. Meningitis affects the meninges alone. Enteroviruses are the most common cause of meningitis in the UK, and herpes simplex virus 1 (HSV)-1 is the most common cause of encephalitis. However, the epidemiology of viral meningitis and encephalitis varies widely across the world, with many arboviruses responsible for CNS infection. Cerebrospinal fluid (CSF) sampling is the key investigation if viral CNS infection is suspected, and the most common viral pathogens can be detected in CSF by polymerase chain reaction (PCR). Additional supporting diagnostic tests may include PCR of faeces, whole blood or throat swabs, alongside magnetic resonance imaging of the brain. Next-generation sequencing may become a future diagnostic option and has helped identify emerging CNS pathogens. Viral meningitis is managed supportively. HSV encephalitis is treated with intravenous aciclovir, but despite therapy, many are left with severe neurological sequelae and mortality is high.