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. It has been found sporadically in humans, birds and other vertebrate 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 is capable of causing fatal neurological disease such as encephalitis in humans and horses, and mortality in certain wild bird species.

2007 Map and Chart of WNV Activity

2006 map and Chart of WNV Activity

2005 map and Chart 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 will not show any symptoms.  However, mild symptoms may include slight fever and/or headache, possibly with skin rash and swollen lymph glands. A rapid onset of high fever with head and body aches, neck stiffness, disorientation, stupor and muscle weakness marks more severe infections.  Those who may be most at risk are persons over the age of 50 and those with compromised immune systems.

The principle route of human infection with West Nile virus is through the bite of an infected mosquito.  Mosquitoes become infected when they feed 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.  For example, you cannot get West Nile virus from touching or kissing a person who has the disease, nor from a health care worker who has treated someone with the disease.

Even areas where mosquitoes do carry the virus, very few mosquitoes (much less than 1%) are infected.  If an infected mosquito bites you, you have less than a 1% chance of severe illness.  The chances of being severely ill from any one mosquito bite are extremely small.

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, persons should avoid bare-handed contact when handling any dead animal and use gloves or double plastic bags to place the carcass in a garbage can.  In keeping with overall public health practice and due to the risk of known food-borne pathogens, people should always follow proper procedures for fully cooking meat.

• Stay indoors at dawn, dusk, and in the early evening.
• Wear light colored long-sleeved shirts and long pants whenever you are outdoors.
• Spray clothing with repellents containing permethrin or DEET since mosquitoes may bite through thin clothing.
• Apply insect repellent sparingly to exposed skin. An effective repellent will contain 30% DEET (N,N-diethyl-meta-toluamide) for adults and 10% 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 an insecticide or insect repellent, 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, or similar water-holding containers.
• Drill 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 holes in downspout extensions. Roof gutters can produce millions of mosquitoes each season.
• Turn over plastic wading pools and wheelbarrows when not in use.
• Change water in birdbaths.
• 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 for more than four days.