West Nile virus is spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. After 10-14 days, the infected mosquito can transmit West Nile virus to people and animals through its bite. The virus is not spread from person-to-person or animal-to-person contact. Routine screening of blood donations since 2003 has greatly reduced the risk of West Nile virus infection through transfused blood.
West Nile Virus
Health care providers, hospitals, laboratories and veterinarians
- Report West Nile Virus in humans or animals at 360.397.8408.
- Reporting requirements (WAC 246101) and West Nile Virus guidelines
How is it spread?
What are the symptoms?
Most people infected with West Nile virus have no symptoms. About 20 percent develop symptoms that include fever, fatigue, headache and muscle or joint pains. These symptoms can last a few days to several weeks. Less than 1 percent of infected people will develop a more serious illness with symptoms that include headache, high fever, stiff neck, disorientation, convulsions, tremors and muscle weakness. Severe cases of the virus may lead to paralysis, coma or death.
Symptoms typically appear three to 15 days after the mosquito bite. People age 50 and older are more likely to develop severe symptoms from West Nile virus.
How is it treated?
There is no specific treatment for West Nile virus infection. In more serious cases, treatment may involve hospitalization where patients can receive intravenous fluids, respiratory support, prevention of secondary infections and nursing care.
What can be done to prevent infection?
Currently there is no vaccine to protect humans from West Nile virus. The best defense against the disease is to control mosquito populations, monitor for the presence of the virus, and prevent mosquito bites.
Don't give mosquitoes a place to breed
Mosquitoes lay eggs in slow-moving or standing water. A small puddle of water can breed thousands of mosquitoes each week. From April to October, when mosquitoes are most active, take steps to prevent mosquitoes from breeding:
- Remove sources of standing water, such as old tires, empty containers, pots, plastic ground covers, and anything else that holds water.
- Change water in bird baths, ponds, pet dishes and animal troughs twice a week.
- Repair leaking faucets and sprinklers.
- Clean clogged gutters.
- Cover trash containers so they don't accumulate water.
- Properly maintain and treat your pool and pond. Be sure pool covers do not hold pockets of water. Ornamental, self-contained ponds may be treated with larvicide to reduce mosquitoes. Follow label instructions and make sure it is for home use.
- Organize neighborhood cleanup activities to remove sources of standing water.
- Report areas of standing water by calling Clark County Mosquito Control’s 24-hour reporting line at 360.397.8430.
Prevent mosquito bites
To reduce the risk of West Nile virus, take the following safety measures to prevent mosquito bites:
- Use mosquito repellent when you are outdoors, especially at dawn, dusk and early evening, when mosquitoes are most active. The most effective repellents contain the active ingredients DEET, Picaridin or oil of lemon eucalyptus. Permethrin also is an effective repellent, but should be applied to clothing only, not directly to the skin.
- Follow directions when using repellents, especially when applying on children. Don't allow children to apply repellents themselves. Visit the Centers for Disease Control for more information on mosquito repellents.
- Install or repair screens on windows and doors so mosquitoes can't get inside.
- If possible, stay indoors during peak mosquito hours. But if being outside is irresistible on a warm summer evening, wear loose-fitting protective clothing such as long-sleeved shirts, long pants, shoes and socks and hats, especially when going into woods or wetland. If heat makes extra clothing uncomfortable, be sure to use repellent.
- Place mosquito netting over infant carriers when outdoors.
Reporting dead birds
The Online Dead Bird Reporting System for West Nile Virus (WNV) surveillance has been discontinued. Research has shown that testing local mosquito populations is the best way to detect the presence of WNV. The Clark County Mosquito Control District will continue to actively monitor and test local mosquito populations.
We wish to thank community members who have diligently reported dead birds over the past years. Your partnership and dedication are much appreciated.
Other state agencies monitor dead birds for avian influenza throughout the year. For questions or reporting, please contact:
- Wild bird die-offs (multiple birds) - Washington State Department of Fish & Wildlife at 1.800.606.8768. Die-offs of five or more wild birds can be reported using the DOH online dead bird reporting form. These online reports will be routed to Washington State Department of Fish & Wildlife.
- Domestic poultry - Washington State Department of Agriculture at 1.800.606.3056.
- Handling dead birds
- Do not handle dead birds with your bare hands. Use, gloves, a shovel or a plastic bag over your hand to pick up a dead bird.
- Double-wrap the bird in two plastic bags and dispose of in your household garbage.
- Do not bring dead birds to Public Health.