West Nile virus

West Nile virus (WNV) causes West Nile fever and West Nile meningitis, encephalitis and West Nile poliomyelitis. It can infect people, birds, mosquitoes, horses and other animals. In Washington State the virus was first found in horses and birds in 2002. The first human infection by WNV in Washington State occurred in 2006.

Most people who are infected with the West Nile virus will not get sick. In those who do become ill, symptoms usually begin between 3 and 14 days after being bitten by an infected mosquito.

About 1 in 5 infected persons will develop West Nile fever, a flu-like illness lasting a few days to several weeks. In addition to fever, symptoms include:

• Fatigue
• Headache
• Loss of appetite
• Muscle aches
• Nausea
• Rash
• Vomiting
• Swollen glands

About 1 in 150 infected people will have one of the more severe and potentially fatal forms of disease (West Nile meningitis, encephalitis or West Nile poliomyelitis) that can include symptoms of West Nile fever and:

• Severe headache
• Neck stiffness
• Decreased level of alertness
• Muscle weakness, tremors, or paralysis
• Sensitivity to light
• Convulsions or coma

West Nile virus is spread to people mainly by the bite of an infected mosquito. Mosquitoes become infected after feeding on birds that carry the virus. WNV is not spread by direct contact with infected animals or people, but care should always be used when handling sick or dead animals. WNV may be spread via blood transfusion and organ transplantation. Blood and organ donations are routinely tested and infected donations are not used.

The risk of getting West Nile virus is very low, but anyone who is bitten by infected mosquitoes can be infected. Older people over 50 years of age have a higher risk of having more serious symptoms.

• West Nile virus in humans is diagnosed by testing blood and/or CSF (cerebrospinal fluid from a spinal tap).
• Contact your healthcare professional if you have symptoms of a possible WNV infection, especially if you recently had mosquito bites.
• There is no vaccine for humans or specific treatment other than supportive care.

• Empty anything outdoors that holds standing water -- any standing water can serve as a mosquito breeding site.
• Change water in birdbaths, fountains, wading pools and animal troughs weekly.
• Make sure that roof gutters drain properly.
• Fix leaky outdoor faucets and sprinklers.
• Make sure that windows and door screens are "bug tight" -- if not, repair or replace them.
• Stay indoors at dawn and dusk when mosquitoes are the most active.
• Wear protective clothing (long sleeves, long pants and a hat) when going into mosquito-infested areas.
• Use mosquito repellent when necessary, and carefully follow the directions on the label. Effective repellents contain DEET, picaridin, oil of lemon eucalyptus, or IR3535.
• Assist elderly neighbors and relatives in these tasks to help keep them safe from mosquito bites.

West Nile virus infects many wild birds including crows, jays and ravens. Increasing numbers of dead birds can be a sign that WNV is present in a community. As with any dead animal, avoid any direct contact. Wear gloves or use a shovel to move the bird. Dead birds can be disposed of by putting them in a plastic bag and then into the garbage.

Public Health tracks and sometimes tests dead birds. For more information about West Nile virus and to report dead birds call 206-205-4394 or visit www.kingcounty.gov/health/westnile.