Aseptic Meningitis

SELECT ARTHROPOD-BORNE VIRUS INFECTIONS

Various mosquito-borne viruses may cause an infectious encephalitis. Treatment is primarily symptomatic, making preventive strategies important, especially for arthropod-borne viruses (arboviruses), such as eastern equine encephalitis virus and West Nile virus (WNV). The related St. Louis encephalitis virus is transmitted mainly in North America during late summer or early autumn and typically causes mild nonspecific symptoms but occasionally an encephalitic illness.

Eastern equine encephalitis virus, found in the Caribbean and eastern United States, infects humans, horses, and some bird species. Other variants of the virus occur in Central and South America, where they cause equine disease. Most infected persons are asymptomatic. When symptoms do occur, they may consists solely of a mild nonspecific flulike systemic illness, with headache, fever, malaise, aching pains, and vomiting, from which complete recovery occurs with 7 to 10 days in the absence of cerebral involvement. In uncommon instances, however, a fulminating encephalitic illness occurs after an incubation period of 3 to 10 days and is characterized by confusion, delirium, irritability, restlessness, seizures, and, eventually, loss of consciousness. The encephalitic illness is associated with a 33% mortality rate, and about Half of the survivors have residual cognitive or other neurologic deficits. There is a pleocytosis in the CSF, with an increased neutrophil count and an elevated protein concentration; glucose level is normal. Serologic diagnosis depends on IgM testing of serum and CSF, and antibody testing of acute- and convalescent-phase serum. MRI most often shows unilateral or bilateral abnormalities (increased T2 signal intensity) of the basal ganglia; the internal capsule, thalamus, brainstem, periventricular white matter, and cerebral cortex may also be involved. There is no specific therapy, and treatment is purely supportive. No vaccine is available, and prevention therefore depends on reducing exposure to mosquitoes.

The West Nile virus, a flavivirus usually found in Africa, West Asia, and the Middle East, was not documented in the Western Hemisphere until 1999. Reservoirs for the virus include humans, horses, certain other mammals, birds, and mosquitoes. In humans, infection may be asymptomatic or lead to mild disease (West Nile fever) with flulike symptoms (sometimes accompanied by a skin rash) that develop within 2 weeks after the bite of an infected mosquito and usually last for only a few days. However, an encephalitis, meningitis, or meningoencephalitis sometimes develops, as may a poliomyelitic illness, and sometimes leads to a fatal outcome. The CSF shows a lymphocytic pleocytosis with elevated protein and normal glucose concentrations. Polymerase chain reaction may be diagnostic, but false-negative results are common. Thus the diagnosis is usually established by serologic assays of blood and CSF. Treatment is supportive; no specific drug treatment is available. Prevention depends on avoidance of infected mosquitoes because no vaccine is available. Residual deficits, such as cognitive changes or muscle weakness, may occur in survivors.

Only gold members can continue reading. Log In or Register to continue