West Nile Virus

Division of Epidemiology
275 East Main Street
Frankfort, KY 40621
502-564-3418 or 3261

West Nile virus (WNV) was first isolated in the West Nile District of Uganda in 1937 and, since, has been found occasionally in humans, birds and other animals in Africa, Eastern Europe, West Asia and the Middle East. First reported in the United States in 1999 in New York City, WNV has since been isolated in 47 states and the District of Columbia. The West Nile virus can cause fatal neurological disease such as encephalitis in humans and horses, and can be fatal in certain wild bird species.

2008 Map of WNV Activity

2007 Map of WNV Activity

2006 Map of WNV Activity

2005 Map of WNV Activity

2004 Map and Chart of WNV Activity

2003 Map and Chart of WNV Activity

2002 Map and Chart of WNV Activity

Most people exposed to WNV will not show any symptoms. However, mild symptoms may include slight fever and/or headache, possibly with skin rash and swollen lymph glands. Rapid-onset high fever with head and body aches, neck stiffness, disorientation, stupor and muscle weakness mark more severe infections. Those who may be most at risk are people age 50 and older and those with weak immune systems.

The principle way people are infected with WNV is through the bite of an infected mosquito. Mosquitoes become infected by feeding on infected birds, which may circulate the virus in their blood for a few days. The virus eventually finds its way into the mosquito's salivary glands. During subsequent blood meals, the virus may be injected into humans and animals, where it can multiply and possibly cause illness.

No. West Nile virus infection is not transmitted from person-to-person.  You cannot get West Nile virus from touching or kissing a person who has the disease, or from a health care worker who has treated someone with the disease.

Even areas where mosquitoes do carry the virus, very few mosquitoes (fewer than 1 percent) are infected. If an infected mosquito bites your risk of severe illness is lower than 1 percent. The chances of being severely ill from any one mosquito bite are extremely low.

No, but several companies are working on developing a vaccine.

No. WNV is not transmitted from animal-to-animal or animal-to-person.  Only an infected mosquito can transmit the virus. However, people should avoid bare-handed contact and use gloves or double plastic bags when handling any dead animal. Good health practices also recommend proper handling and cooking of meat to avoid and lessen the risk of any food-borne illness.

• Stay indoors at dawn, dusk and early evening when mosquitoes are most active.
• Wear light colored long-sleeved shirts and long pants when outdoors.
• Spray clothing with repellents containing permethrin or DEET (N,N-diethyl-meta-toluamide) since mosquitoes may bite through thin clothing.
• Apply insect repellent sparingly to exposed skin. Effective repellents contain 30 percent DEET for adults and 10 percent DEET for children. Repellents may irritate the eyes and mouth, so avoid applying repellent to the hands of children. Do not use DEET on infants.
• Whenever you use insecticides or insect repellents, be sure to read and follow the manufacturer’s directions for use as printed on the product.
• Note: Vitamin B and ultrasonic devices are not effective in preventing mosquito bites.

Visit the American College of Physicians Web site: Mosquitoes and mosquito repellents: A clinician’s guide, (Mark S. Fradin, MD. Annals of Internal Medicine. June 1, 1998;128:931-940). You can also find information on insect repellents containing DEET at the Environmental Protection Agency (EPA) Web site or by contacting your local pharmacist.

To reduce the mosquito population around your home and property, reduce the amount of standing water available for mosquito breeding.

You can follow these simple steps:

• Remove all discarded tires on your property. Used tires are one of the primary breeding areas for mosquitoes.
• Dispose of tin cans, plastic containers, ceramic pots and similar water-holding containers.
• Drill drain holes in the bottom of recycling containers left outdoors.
• Make sure roof gutters drain properly and clean clogged gutters in the spring and fall. Put drain holes in downspout extensions. Roof gutters can produce millions of mosquitoes each season.
• Drain and turn plastic wading pools and wheelbarrows upside down when not in use.
• Change water in birdbaths regularly.
• Clean vegetation and debris from edges of ponds.
• Clean and chlorinate swimming pools, outdoor saunas and hot tubs. Aerate or add fish to ornamental ponds. 
• Drain water from pool covers and tarps.
• Use landscaping to eliminate standing water that collects on your property. Mosquitoes may breed in any puddle that lasts more than four days.