Using Digital Mapping to Combat the West Nile Virus
By Kathy Millar

Earthquakes, floods and animal movements are routine targets for digital mapping at the U.S. Geological Survey. But in the summer of 2000, few projects are as important as the work USGS is doing to track and help manage the spread of West Nile virus, a strain of encephalitis that in 1999 left 62 people in New York infected and 7 of them dead.

Using state-of-the-art, multi-layered mapping techniques, USGS is providing critical surveillance information to the Centers for Disease Control and Prevention, USDA’s Animal and Plant Health Inspection Service, State wildlife agencies, and State and local health and vector control agencies. Agencies in 19 states and localities along the Atlantic and Gulf coasts are engaged in the effort, linked electronically to the online interactive and multimedia maps updated regularly by USGS.

Mapping is a web-based Geographic Information System (GIS) that requires software, hardware, trained users, analysis, and any amount of raw data on any subject or a combination of subjects. The purpose is to create visual displays to highlight issues or problems — in this case, the spread of a life-threatening virus.

West Nile virus -- first isolated in Africa in 1937 -- had spread by the end of the century to Israel, Eurasia, Asia and Western Europe. But the virus had never been seen before in the U.S. until it surfaced in New York last August.

No one knows for sure how the West Nile virus made it across the Atlantic. A specialist in mosquito-borne diseases from the United States Army Medical Research Institute for Infectious Diseases (USAMRIID) speculates it may have entered the U.S. last year via an infected mosquito trapped on a transatlantic flight to New York. "When the plane landed," he says, "the mosquito — who hadn’t eaten for 7 or 8 hours — headed for the nearest meal, probably a crow."

West Nile Virus: Getting it and Getting Rid of It

West Nile virus is transmitted to humans, crows and other birds through the bite of an infected mosquito, and there are three separate species that carry the disease: one species feeds during the day, while the other two feed during the evening and at night. Many of the fatalities in New York were senior citizens who contracted the virus in the evening while working in their gardens.

Left unmonitored, the virus could pose a real health problem for the United States, especially for the population most vulnerable to the disease — Americans over 50 and people with weakened immune systems. Public officials point out that there is no vaccine for West Nile Virus and no specific treatment. Once West Nile virus has been identified as a threat in a specific area, the only way to eliminate the disease is to eliminate the mosquitoes that carry it -- spray.

Using Data Mapping to Eliminate the Threat

Effective mosquito control programs, however, are both difficult and expensive to implement. And there has never been a need before in the U.S. to mount a mosquito control program of any size or scope. To ensure the elimination of infected mosquitoes in a cost-effective way, communities need to spray the right species of mosquitoes at the right times and in the right places. Public health officials need to track the carriers of this virus, its victims, movement, intensity and potential to understand when and where to spray. And that’s where USGS and its digital mapping capabilities are making a difference.

Before the spread of the virus abated late last fall, areas affected by West Nile virus included New York, New Jersey, Connecticut and Baltimore County, Maryland. In the spring of 2000, public health officials confirmed that mosquitoes carrying the West Nile Virus had successfully survived winter, and that there was reason to believe that the virus might have spread southward from New York, carried down the eastern seaboard by migrating birds.

On July 8, 2000 health officials in New York confirmed that dead crows found in Long Island and Westchester had tested positive for the West Nile Virus. Infected birds have also been found this summer in New Jersey.

Nationalatlas.gov Lets Users Follow Progression of WNV

Health practitioners, veterinarians and citizens who are interested in tracking West Nile virus through the rest of the summer and fall — or who have information to share -- can visit the National Atlas virus page. USGS is advertising the WNV maps as a "new addition" and says "These maps and charts are designed to illustrate documented occurrences of WNV over time. Let your cursor roam over the map and images and enjoy the exploration. The file sizes of these Shockwave maps range from 100 Kb to 150 Kb."

Each week, the National Atlas will include a new series of maps generated by ongoing WNV surveillance activities led by the Centers for Disease Control and Prevention (CDC). Maps are available in three types of mapping services: online interactive maps (over 100 layers of information), dynamic multimedia maps, and high quality maps for printing and reproduction. Printable maps — which are updated weekly -- offer users six separate categories of information: Human cases, veterinary cases, wild bird cases, sentinel flock surveillance, mosquito surveillance and surveillance area.

Precautionary Measures You Can Use

The interactive and online maps provided by USGS are an excellent resource for health practitioners and citizens who want to learn more about the disease and ways to prevent its spread. Until the threat is eliminated, however, there are precautionary measures every American can and should consider:

• WNV is most dangerous to people over 50, and individuals with weakened immune systems — adults should use mosquito repellent with a high percentage of the ingredient known as DEET (up to 30%). Do NOT use repellents containing DEET or potentially dangerous chemicals on children or infants without consulting a physician -- parents should consult a pediatrician regarding appropriate types of mosquito repellent for children of different ages. Always use mosquito repellent when working or playing outdoors, at the beach and near any body of water.

• Remember that the mosquitoes that carry WNV feed during the day, at dusk and at night. Wear cool, dark, protective clothing that covers legs, feet, ankles, etc. Do not wear perfume or other substances that may attract mosquitoes. Be careful when working in gardens or around water.

• Eliminate standing or stagnant water. Check old tires and gutters for standing water and keep animal/pet dishes inside if possible. If it is impossible to eliminate all sources of water outdoors, there are chemicals (Mosquito Dunk, for example) available for use in swimming pools, bird baths and fish ponds that are often toxic for mosquitoes but harmless to people, birds and fish.

• Do not handle dead birds, crows or any other variety, if the cause of death is not readily apparent. Advise children not to handle dead birds. Health officials at the Centers for Disease Control and Prevention say it is unlikely human beings can contract the West Nile virus by handling infected birds but the obvious rule of thumb should be better safe than sorry. If you find a dead crow or other bird whose cause of death is not apparent, call your public heath department. Dogs and cats are not carriers of WNV and are not at high risk, even if they do come in contact with an infected bird.

• Support county and community mosquito control programs. Be responsible for public health education in your community. Initiate dialogue at the local level, share information with at-risk populations and learn all you can about West Nile virus -- how it is spread and what your community can do to combat it.

• Symptoms of West Nile virus include flu-like symptoms, an abrupt onset of moderate to high fever and sometimes chills, headache (often frontal), sore throat, backache, myalgia, fatigue, conjunctivitis, rash spreading from trunk to extremities and head, nausea, abdominal pain, diarrhea and respiratory symptoms.

• If you are bitten by a mosquito, don’t panic. The majority of mosquitoes will not be WNV carriers.

• If you think you might have contracted West Nile virus, don’t panic. Ninety percent or more infected with the disease recover completely. Call your physician or public health department and arrange for the appropriate testing.

• If you have information or data that might be valuable as surveillance mapping material, contact the U.S. Geological Survey or the Centers for Disease Control and Prevention and ask that your information be added to their weekly updates. Once WNV has been identified in a certain area, scientists note that the disease is likely to reemerge over the course of many years - be aware and make mosquito control a part of your regular routine every year during the summer and fall.

For More Information

For more information about USGS surveillance contact Linda Glaser at 608-270-2446. For information on West Nile virus and other wildlife diseases, contact or Dr. Robert McLean at the USGS National Wildlife Health Center; 608-270-2401 or visit the website.

To learn more about USGS research programs and activities, visit the main web site for USGS.

About the Author

Kathy Millar, a writer at the National Partnership for Reinventing Government, can be reached at 304-728-3051 x255 or by email at k.millar@jctc.org.