West Nile Virus home
CONTENTS: Disease description | Risk | Treatment |
West Nile Virus (WNV) is an RNA Flavivirus related to the viral complex that causes St. Louis encephalitis and Japanese encephalitis. In 1937 an Ugandan woman was the first person diagnosed with West Nile viral fever. Since then numerous WNV outbreaks have occurred in Africa, Europe, and the Middle East. WNV was first detected in North America in the summer of 1999 in New York City.
Dr. Deborah Asnis at Flushing Hospital Medical Center worked with the first WNV encephalitis patients in 1999 in New York City. Asnis and collogues describe human WNV disease: "The incubation period of West Nile fever is five to fifteen days. If infected, approximately 1 in 140-300 people will become clinically ill. The clinical presentation is characterized by a flu-like illness with fever, headache, backache, and myalgia lasting three to six days. Pharyngitis, conjunctivitis, nausea, vomiting, diarrhea, and abdominal pain are also reported. About one-half develop a nonpruritic, roseolar, or maculopapular rash on the chest, back, and arms that lasts seven days. Diffuse lymphadenopathy is also common. Rarely, neurological infection ranging from aseptic meningitis, meningoencephalitis, myelitis, optic neuritis, or polyradiculitis can occur. The most severe neurologic disease is seen in the elderly and, less commonly, in children. Extraneurologic inflammation can include myocarditis, pancreatitis, and hepatitis. Common laboratory findings include leukocytosis, leukopenia, and, in neurological infections, CSF pleocytosis with elevated protein. Virus can be recovered from the blood in an immunocompetent febrile patient for up to ten days. In the immunocompromised patient, viral isolation can be prolonged up to 22 to 28 days after infection. Viremia peaks between four to eight days, but the concentration is usually low at 103/mL. Standard precautions should be followed with handling specimens. Virus is not found in feces, urine, or throat washings. The diagnosis is made by serology, PCR, or viral isolation. Serum IgM detection by antibody-capture enzyme immunosorbent assay (EIA) is one of the best methods for identification. The presence of IgM in CSF reflects intrathecal production." (Annals of the New York Academy of Sciences 951: 161-171.)
The South Dakota Department of Health and the CDC recommend that individuals with severe or unusual headaches seek medical care as soon as possible. We encourage a high index of suspicion for arboviral encephalitis. Suspect clinical serum or CSF should be submitted to the State Public Health Laboratory (1-800-592-1861). There is no specific WNV treatment, but supportive therapy is essential. No human vaccine is available to prevent WNV disease. (Return to contents)
Anyone in the areas where WNV has been detected and there are human biting mosquitoes is at risk of becoming ill. Individuals older than 50 years are the greatest risk of becoming ill and dying. The WNV risk season ends when mosquitoes are no longer active, i.e. after the hard freeze. (Return to contents)
There is no specific treatment for West Nile Virus. In more severe cases, intensive supportive therapy is indicated, i.e., hospitalization, intravenous (IV) fluids, respiratory support (ventilator) if needed, prevention of secondary infections (pneumonia, urinary tract, etc.), and good nursing care. Currently there is no vaccine for WNV. (Return to contents)
