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WEST NILE VIRUS INFECTION
West Nile virus (WNV), a single-stranded RNA virus in the Flaviviridae family, is an enzootic agent most commonly found in Africa, Europe, and Asia. It is transmitted among wild birds (e.g. crows, ravens, jays) by Culex mosquitos. Since 1999 there has been geographic expansion of the virus within the US, with human cases in all of the contiguous states and ~2700 deaths to date. Although transmitted primarily by mosquito bites, transmission can also occur via blood transfusions, solid organ transplantation, and possibly breastfeeding.
WNV infection most commonly occurs between late spring and early fall, during periods of active mosquito feeding. Approximately 80% of infections are clinically asymptomatic. In symptomatic patients, manifestations include fever, headache, malaise, anorexia, nausea, vomiting, eye pain, lymphadenopathy, encephalitis, myalgias, and muscle weakness. Older patients have a higher risk of more severe neurologic disease.
An exanthem occurs in 25%โ50% of symptomatic patients with WNV infection. It has been described as a macular, papular, psoriasiform, or erythematous eruption. Both predominance on the extremities and small punctate lesions have been reported. Development of a rash may be associated with decreased risk of encephalitis and death from WNV. The diagnosis is confirmed by serum or cerebrospinal fluid IgM ELISA or RT-PCR. Treatment is supportive; preventive measures include reducing the number of vector mosquitoes and avoidance of mosquito bites.