Acute viral infection of the meninges is the most common cause of meningitis. It often occurs as combined meningo-encephalitis and in many cases it is a diagnosis of exclusion after investigating for bacterial or tuberculous meningitis.
A variety of viruses may infect the meninges including enteroviruses, mumps, herpes simplex, HIV and Epstein–Barr virus.
In viral meningitis there is a predominantly lymphoid immune reaction without the formation of pus or adhesions, there is no cerebral oedema unless encephalitis occurs.
Patients present with headache usually over 1–2 days, fever, nausea, photophobia, malaise and neck stiffness. Rash, upper respiratory symptoms and occasionally diarrhoea may be present. There may be evidence of genital ulcers in those with primary HSV-2 infection, but these are absent in recurrent infections.
A lumbar puncture should be performed if meningitis is suspected. The cerebrospinal fluid (CSF) is usually clear, with predominant lymphocytes, but early in the illness, polymorphs may predominate.
Culture is possible, but rarely useful clinically as it takes up to 2 weeks. PCR has been used in some cases to speed diagnosis and hence stopping antibiotics.
CT brain is normal.
If bacterial meningitis is suspected, broad-spectrum antibiotics must be given without delay. Analgesia is given for headache but no specific treatment is indicated in most forms of viral meningitis. Generally, it is a benign self limiting condition lasting 4–10 days.