What is West Nile Virus?

West Nile virus is a flavivirus (a genus of Japanese Encephalitis and closely related to Louis Encephalitis) commonly found in Africa, West Asia and the Middle East (it was first discovered in Uganda, Africa in 1937). It was discovered in the United States in 1999 in the New York City area and has been moving across the U.S. since.

WNv is primarily a mosquito/bird disease, but incidental infections can occur with humans and many other animals. Mosquitoes become infected when they feed on infected birds, such as ravens and crows. After an incubation period of 5 to 15 days, the mosquito can then transmit the virus to humans and animals by biting them. Following this transmission, the virus multiplies in the bloodstream. In severe cases the virus crosses the blood-brain barrier, reaching the brain and causing inflammation of the brain tissue. This inflammation interferes with the central nervous system.

Questions & Answers

Q. What is the basic transmission cycle?

A. Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. Infected mosquitoes can then transmit WNv to humans and animals while biting to take blood. The virus is located in the mosquito's salivary glands. During blood feeding, the virus may be injected into the animal or human, where it may multiply, possibly causing illness.

Q. What Are the Symptoms of WNv?

Serious Symptoms in a Few People. About one in 150 people infected with WNv will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, paralysis and even death. These symptoms may last several weeks, and neurological effects may be permanent.

Milder Symptoms in Some People. Up to 20% of the people who become infected have symptoms such as fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back. Symptoms can last for a few days or many weeks or months.

No Symptoms in Most People. Approximately 80% of people (about 4 out of 5) who are infected with WNv will not show any symptoms at all.

Q. What Is the Risk of Getting Sick from WNv?

A. Anyone at any age can be infected with WNv and become sick. Though people over 50 are at higher risk to get severe illness, serious illness has occurred if every age group and being young is not a defense against this disease. Being outside means you're at risk. The more time you're outdoors, the more time you could be bitten by an infected mosquito. Pay attention to avoiding mosquito bites if you spend a lot of time outside, either working or playing. Risk through medical procedures is very low. All donated blood is checked for WNv before being used. The risk of getting WNv through blood transfusions and organ transplants is very small, and should not prevent people who need surgery from having it. If you have concerns, talk to your doctor.

Q. What Should I Do if I Think I Have WNv?

A. People typically develop symptoms between 3 and 14 days after the infected mosquito bites them. Milder WNv illness usually improves by itself and people do not necessarily need to seek medical attention for this infection (though they may choose to do so). If you develop symptoms of severe WNv illness, such as unusually severe headaches or confusion, seek medical attention immediately. Severe WNv illness usually requires hospitalization. Pregnant women and nursing mothers are encouraged to talk to their doctor if they develop symptoms that could indicate WNv infection.

Q. What do I do if I see a dead bird?

A. If you find a dead bird: Don't handle the body with your bare hands. Contact your local health department for instructions on disposing of the body.  Report Sick, Injured or Dead Animals to WDFW  (Washington State Department of Fish and Wildlife) at this link:  Bird Reporting