Viral Meningitis and Encephalitis

Many viruses can invade the central nervous system (CNS). Viral CNS infections (often called aseptic meningitis) may be asymptomatic or associated with only mild symptoms, but they can occasionally cause severe meningitis or encephalitis. The diagnostic criteria for the acute aseptic meningitis syndrome are as follows: ▪. Signs and symptoms of acute meningeal irritation; ▪. Mononuclear cell predominance in cerebrospinal fluid (CSF); ▪. Absence of detectable bacteria in the CSF; ▪. Absence of parameningeal or systemic illness; ▪. Brief and benign illness. The diagnostic criterion for encephalitis is alteration of consciousness or focal neurologic findings with evidence of meningeal inflammation. Therefore, the term meningoencephalitis may be appropriate in many cases. An estimated 8000 to 12,000 cases of acute aseptic meningitis occur annually in the United States. Approximately 1000 to 2000 cases of encephalitis are reported annually to the Centers for Disease Control. Viral causes of meningoencephalitis are numerous, but clinical signs and symptoms alone usually cannot establish a specific diagnosis. However, new laboratory methods are becoming available that will aid in rapid and specific identification of viral agents and will lead to new knowledge of the epidemiology of these viral infections.