US Geological Survey
Center for Integration of Natural Disaster Information

West Nile Virus Maps - 2001

a mosquito

Year 2000 Cumulative Reports
2001 Surveillance Activity

National and State Maps

Note: 2001 National and State Maps

These maps reflect the final reported and verified information from the 2001 West Nile Virus Surveillance Database. The database includes events through December 28, 2001.



Since the 1930s, West Nile virus (WNV) has been commonly reported to cause asymptomatic infection and fevers in humans in Africa, West Asia, and the Middle East. But, human and animals infection had never been documented in the Western Hemisphere until 1999. In 1999 and 2000, outbreaks of WNV encephalitis (inflammation of the brain) and other febrile illnesses were reported in persons living in the New York City metropolitan area. In these two years, 83 human cases of West Nile illness were reported; 9 died. In 2001, the first cases of WNV encephalitis outside of the New York City metro area occurred when 2 cases were reported from a rural Florida county in July and August.

WNV is transmitted to humans through mosquito bites. Mosquitoes become infected when they feed on infected birds that have high levels of WNV in their blood. Infected mosquitoes can then transmit WNV when they feed on humans or other animals.

WNV is not transmitted from person to person and there is no evidence that a person can get infected by handling live or dead infected birds. But, to add a further level of safety, if birds or other potentially infected animals must be handled, a protective barrier (e.g., gloves, inverted plastic bags) should be used.

Most WNV infected humans have no symptoms. A small proportion develops mild symptoms that include fever, headache, body aches, skin rash and swollen lymph glands. Less than 1% of infected people develop more severe illness that includes meningitis (inflammation of the spinal cord) or encephalitis. The symptoms of these illnesses can include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. Of the few people that develop encephalitis, a small proportion die but, overall, this is estimated to occur in less than 1 out of 1000 infections.

There is no specific treatment for WNV infection or vaccine to prevent it. Treatment of severe illnesses includes hospitalization, use of intravenous fluids and nutrition, respiratory support, prevention of secondary infections, and good nursing care. Medical care should be sought as soon as possible for persons who have symptoms suggesting severe illness.

Individuals can reduce their contacts with mosquitoes by taking these actions:

When outdoors, wear clothing that covers the skin such as long sleeve shirts and pants, apply effective insect repellent to clothing and exposed skin, and curb outside activity during the hours that mosquitoes are feeding which often includes dawn and dusk. In addition, screens should be applied to doors and windows and regularly maintained to keep mosquitoes from entering the home.

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The following links provide other information on the West Nile Virus:

USGS West Nile Virus Page
USGS National Wildlife Health Center, Madison, Wisconsin
USGS National Biological Information Infrastructure West Nile Virus Page
Centers for Disease Control and Prevention questions and answers
Centers for Disease Control and Prevention West Nile Virus Background Page


West Nile Virus Maps from the National Atlas, 2000
Cumulative Report Maps for the year 2000 from the National Atlas
Cumulative Bird Cumulative Human Cumulative Veterinary Cumulative Mosquito Cumulative Sentinel Flock

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2001 Surveillance Activity

The Centers for Disease Control and Prevention is working with the U.S. Geological Survey, U.S. Department of Agriculture Animal and Plant Health Inspection Service, state wildlife agencies, and state and local health and vector control agencies to track the occurrence of West Nile virus (WNV). Organizations in the lower 48 States and localities are actively participating in this program. 

The West Nile Virus Surveillance System is intended to monitor the geographic and temporal spread of WNV over the contiguous United States, to further develop national public health strategies for WNV surveillance, prevention, and control, to develop a more complete regional picture of the geographic distribution and incidence of similar viruses, and to provide national and regional information to public health officials, elected government officials, and the public. There are five surveillance activities: