Clinical

There are several viruses that can cause meningitis and/or encephalitis. Listed below are the viruses most commonly associated with these symptoms. However, it must be remembered that any virus (e.g. rubella virus and rotavirus) can cause encephalitis rarely. For more details on individual viruses, refer to virus-specific pages.

Viral encephalitis

• Herpes simplex virus encephalitis is caused by HSV type 1 or rarely type 2. Symptoms include fever, severe headache, drowsiness, fits and/or unconsciousness. Prompt antiviral treatment with intravenous aciclovir is essential, since herpes encephalitis can have a mortality rate of 70% when untreated. Patients very rarely have HSV-type vesicles on the skin. Even when prompt treatment is given, about 10–30% of patients will be left with some sort of neurological deficit.

• Varicella-zoster virus can cause meningitis or meningo-encephalitis as a result of reactivation of the virus in the brain. As with HSV, few patients have VZV lesions on the skin. Patients are usually experiencing zoster with no external manifestations. One of the most feared but rare complications of chickenpox is encephalitis, which can be fatal, especially in pregnant women, and should be treated promptly with high dose intravenous aciclovir.

• Other viruses, such as arboviruses (e.g. Japanese encephalitis virus) or rabies virus cause potentially fatal encephalitis, almost always acquired abroad. Any virus can cause encephalitis and the clue to the causal virus often lies in the other symptoms (e.g. rubella rash or rotavirus diarrhoea and vomiting) or their travel history.

Neonates can be born with encephalitis as a result of congenital infection.