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2012 state incidence map. Courtesy CDC.

Clinical Manifestations of WNV

Most people infected with WNV are asymptomatic; however, about 20-30% will have fever, head and body aches, swollen lymph nodes, and/or a rash. The incubation period is 2-14 days after the mosquito bite.
Less than 1% develop neuroinvasive disease. WNV meningitis is typical of other viral meningitis cases and symptoms are mild, to include fever, headache, and neck stiffness. WNV encephalitis has symptoms of fever with altered mental status, focal neurological deficits, or tremors similar to Parkinson's disease. WNV can also cause flaccid paralysis, reminiscent of polio, with damage to the anterior horn cells leading to limb paresis. It can progress to respiratory paralysis and patients may require ventilator support. Guillain-Barre, cardiac arrhythmias, hepatitis, pancreatitis, orchitis, rhabdomylysis, and eye diseases have been reported rarely.
In 2012 there was a large outbreak in the United States (see map on the right) of 5,674 cases, in which 51% of the cases presented with neuroinvasive disease: 56% encephalitis, 36% meningitis, and 8% flaccid paralysis. The highest incidence of neuroinvasive disease was seen in people aged 70 years and older and 9% died.
There is no antiviral treatment and no vaccine for WNV.