West Nile Virus

West Nile virus is a disease spread by infected mosquitoes that mostly affects birds. It can also be transmitted to other animals and people.

Most people do not become very sick. But in some cases, West Nile virus can cause encephalitis, or swelling of the brain.

How West Nile virus is spread

In most cases, the virus is spread by the bite of an infected mosquito. Mosquitoes become infected with the virus when they bite an infected bird. They can then spread it to other animals or people.

You can get West Nile virus from:

• The bite of an infected mosquito
• Blood transfusions or organ donations from an infected donor. (You cannot get West Nile virus by donating your blood.)
• Pregnant mothers to unborn children
• Breast milk (but mothers are still encouraged to breastfeed their babies).

You can't get West Nile virus by handling live or dead infected birds. But it's still important to wear gloves when handling any dead animal. Wash your hands thoroughly with hot soapy water after you've removed your gloves.

There is a very low infection rate of West Nile virus in dogs and cats. It also causes illness and death in horses, but a vaccine for horses is available. If you are concerned, contact your veterinarian.

Illness and symptoms

Most people who are infected with West Nile virus do not have any symptoms or get sick at all. Less than one percent of people who get bitten and become infected get severely ill.

Some people who are infected may develop a mild illness, with fever and body aches. The elderly are at greatest risk for serious illness. See your doctor or clinic if you experience symptoms:

• Fever
• Headache
• Nausea
• Body aches
• Other symptoms

In rare occasions, the disease may progress to encephalitis that may cause severe headache, confusion, weakness, or dizziness. The time between a mosquito bite and onset of illness ranges from 3 to 14 days in humans.

Prevention and Personal Protection

You can help prevent the spread of West Nile Virus by reducing the number of mosquitoes around your home and neighborhood and protecting yourself from mosquito bites.

Report Dead Birds

Some birds, especially corvids such as crows and jays, are known to get sick and die from West Nile virus. Wild bird die-offs can indicate the presence of West Nile virus in our community. Multnomah County Vector Control checks dead birds for West Nile seasonally between May 15 and September 30.

To report a dead bird outside of these dates:

• Wildlife Care Center | 503-292-0304
• Oregon Department of Fish and Wildlife, Sauvie Island Wildlife Area | 503-621-3488

More Information

• Oregon Public Health - West Nile Virus Activity 
• National Pesticide Information Center – Choosing Repellants

Centers for Disease Control & Prevention:

• West Nile Virus
• Dead Birds
• For Travelers: Protection Against Mosquitoes

Documents

• West Nile Virus FAQs - English (42.72 KB)
• West Nile Virus FAQs - Chinese (424.1 KB)
• West Nile Virus FAQs - Korean (247.23 KB)
• West Nile Virus FAQs - Russian (189.91 KB)

• DEET Brochure (for seniors) (151.62 KB)
• Proper insect repellent use for children (31.82 KB)
• "Fight the Bite" poster (multiple languages) (3.16 MB)