West Nile Virus Spreads Across Eastern U.S.
Abstract & Commentary
Source: West Nile virus activity—Eastern United States, 2001. MMWR 2001;50:617-619.
Meningoencephalitis from the West Nile Virus (WNV) first was reported in this country in 1999. The first cases were in Queens, NY, and all cases that year were localized to the New York City area. A national surveillance system since has been developed to monitor the spread of the virus and identify areas at risk for WNV infections.
This year, the first human case of WNV was identified in July in an elderly Florida man. Animal surveillance so far this year has detected disease in birds in nine states—Connecticut, Florida, Georgia, Maryland, Massachusetts, New Jersey, New York, Rhode Island, and Virginia—and the District of Columbia. Twice as many diseased birds have been detected this year compared to 2000. Because birds serve as reservoirs for this mosquito-borne virus, the geographically diverse distribution of infected birds indicates that residents of most of the densely populated areas of the Eastern United States are at risk for contracting WNV.
Comment by David J. Karras, MD, FAAEM, FACEP
WNV is a flavavirus closely related to the St. Louis encephalitis virus. Birds, particularly crows, are reservoirs of disease that is spread to humans by common culex-species mosquitoes. In WNV-endemic regions of Africa, Europe, and Asia, WNV infection is characterized by a mild febrile illness. The outbreaks of severe disease in the United States are characteristic of illnesses in populations with low levels of disease immunity.1
Detailed data recently have been published regarding the initial WNV outbreak in the United States during the summer and fall of 1999.1 Of 59 hospitalized patients with confirmed WNV infections, 63% had encephalitis and 29% had meningitis alone. The median age of the victims was 71 years. Almost all had fever; weakness, nausea, vomiting, headache, and altered mental status each were noted in about half of patients. Ten percent had diffuse flaccid paralysis. Cerebrospinal fluid showed evidence of viral infections, with modest elevations in white blood cell count (38 ± 12 cells/mm3) and protein (104 ± 117 mg/dL). Seven patients (12%) died.
The mosquito season, and thus the risk of WNV infection, continues until late fall. Physicians in the Eastern United States should suspect WNV infection in any patient who presents with signs of encephalitis or viral meningitis, particularly when the patient is older or has muscle weakness.
References
1. Nash D, et al. Outbreak of West Nile virus infection in the New York City area in 1999. N Engl J Med 2001; 344:1807-1814.
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