Diagnosis of West Nile Virus

Clinical Features:
Most people who are infected with the West Nile virus will not show any signs of illness. An estimated 20% of the people who become infected will develop West Nile Fever: usually mild symptoms, including fever, headache, and body aches, occasionally with a skin rash on the trunk of the body and swollen lymph glands. Some WN Fever cases will become severe and can leave lasting neurologic effects. It is estimated that 1 in 150 persons infected with the West Nile virus will develop a more severe form of disease called West Nile Encephalitis and/or Meningitis. The symptoms of severe infection include headache, high fever, stiff neck, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. Symptoms of mild disease will generally last a few days. Symptoms of severe disease may last several weeks, although neurological effects may be permanent, and in rare cases is fatal.

More information on the clinical presentation of WNV can be found at: www.cdc.gov/ncidod/dvbid/westnile/resources/fact_sheet_clinician.htm

Clinical Information Needed to Aid in WNV Diagnosis

• Date of symptom onset
• Date sample collected
• Patient Symptoms
• Past vaccination for Yellow Fever
• Exposure to mosquitoes
• Recent blood transfusion or organ transplantation
• Travel history
• History of pregnancy, birth, & breastfeeding

Indications for Testing

• Encephalitis cases of unknown etiology.
• Patients with flaccid paralysis, myelitis or neurological symptoms following a febrile illness.
• Patients with onset of compatible illness within 2 weeks of receiving blood products.
• Pregnant or breast-feeding women with a compatible febrile illness and exposure history.
• Aseptic meningitis cases, although at this time of year, many such cases are caused by enteroviruses; CSF testing by PCR for enterovirus is recommended.
• Clinically compatible illness during transmission season. Providers should consider if there is any clinical value in testing patients with mild fevers of unknown origin in the absence of neurological signs.

UHL does NOT recommend testing of asymptomatic persons concerned about exposure, mild uncomplicated febrile illness, or screening of asymptomatic pregnant or breast-feeding women.