Meningitis and meningoencephalitis are relatively common and fatal if untreated. The clinical onset is rarely acute. During the weeks of illness before diagnosis, asymptomatic intervals are not uncommon. The usual presenting feature is a persistent headache, alone or with fever. Nausea, dizziness, ataxia, impaired mentation, and irritability are also common.
Seizures are rare initially but occasionally develop as the disease progresses.
Decreased visual acuity, diplopia, and facial numbness and weakness also occasionally develop. Papilledema is present in about one third of cases and cranial nerve palsies in about one fifth of cases. Endophthalmitis and catastrophic vision loss caused by invasion of the optic nerve may occur. Although patients sometimes complain of a stiff neck, fully developed meningismus is frequently absent. Focal neurologic lesions, except those resulting from the effects of the basilar meningitis on the cranial nerves, are quite rare.