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Section 3. Summaries of Infectious Diseases
West Nile Virus
Clinical ManifestationsEtiology
Epidemiology
Diagnostic Tests
Treatment
Isolation of the Hospitalized Patient
Control Measures
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CLINICAL MANIFESTATIONS
Most infections attributable to West Nile virus (WNV) are asymptomatic. Approximately 20% of infected people will develop a systemic febrile illness called West Nile fever (WNF), and less than 1% will develop neuroinvasive disease, such as aseptic meningitis, encephalitis, or flaccid paralysis. The risk of neuroinvasive disease increases with age and is highest among adults older than 60 years of age. Patients with WNF typically have an abrupt onset of fever, headache, myalgia, weakness, and often, abdominal pain, nausea, vomiting, or diarrhea. Some patients have a transient maculopapular rash. The acute phase of illness usually resolves within several days, but fatigue, malaise, and weakness can linger for weeks. Patients with neuroinvasive disease may present with neck stiffness and headache typical of aseptic meningitis, mental status changes indicating encephalitis, focal neurologic deficits, movement disorders, such as tremor or Parkinsonism, seizures, or acute flaccid paralysis with or without meningitis or encephalitis. Isolated limb paralysis can occur without fever or apparent viral prodrome. Flaccid paralysis caused by WNV infection is identical clinically and pathologically to poliomyelitis caused by poliovirus, with damage of anterior horn cells, and may progress to respiratory muscle paralysis requiring mechanical ventilation. Guillain-Barré syndrome also has been reported after WNV infection and can be distinguished from anterior horn cell damage by clinical manifestations and electrophysiologic testing. Cardiac dysrhythmias, myocarditis, rhabdomyolysis, optic neuritis, uveitis, chorioretinitis, orchitis, pancreatitis, and hepatitis have been described rarely after WNV infection.
Most patients who develop WNF or aseptic meningitis recover completely. Patients with encephalitis may have residual neurologic deficits, and patients with flaccid paralysis may not recover full neuromuscular function. The case-fatality rate after neuroinvasive WNV disease is approximately 9% among
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