Arboviruses

Arboviruses (arthropod-borne) belong to various families but share common features: (a) they are major causes of epidemics in particular geographic areas; (b) the diseases are acquired by mosquito and tick bites, commonly in late summer or early fall; and (c) from the site of inoculation, the viruses reach the nervous tissue through the bloodstream, evoking an aseptic meningitis or meningoencephalitis. The prognosis varies; it is less favorable among children and elderly individuals.

St. Louis encephalitis, the most common viral encephalitis, occurs throughout the United States.

It has a relatively low mortality (5%-10%) and good recovery.

Eastern encephalitis has a high mortality (35%), and residual disabilities are severe, particularly in children.

Western encephalitis has low mortality, but sequelae are common in children.

Venezuelan and California encephalitides occur frequently in children. Mortality is high in cases of Venezuelan encephalitis and low in cases of California encephalitis.

Japanese encephalitis, the most common epidemic encephalitis, primarily affects children. The mortality is high (20%-35%) and, in survivors, the sequelae are serious.

West Nile virus infection occurs in several regions of the United States. The infection produces a meningoencephalitis or a myelitis with flaccid paraparesis mimicking poliomyelitis. Immunosuppressed and elderly individuals are at particular risk for the infection.

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