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Seattle woman has first human case of West Nile virus contracted in King County

SEATTLE -- A Seattle woman has tested positive for West Nile virus, marking the the first locally contracted human case of West Nile virus reported in King County, according to King County Public Health officials. 

The woman, who is in her 40s, reported symptoms including fever, headache, stiffness in the neck, and a rash.

She was hospitalized for one day in mid-September and has since recovered. She was most likely infected in late August in Seattle but possibly could have been infected on a day trip to Bainbridge Island, King County Public Health said in a news release.

Before this case, all reported cases of West Nile virus infection to King County residents had a history of travel either out of Washington state or to eastern Washington, where about six people are infected each year. 

West Nile virus is most commonly transmitted to people, horses, and some types of birds through mosquito bites. Most people who become infected don’t become ill.

About one in five people with West Nile virus experience symptoms including fever, body aches, fatigue, headache, rash, vomiting, diarrhea, or joint pain.

Less than 1 percent develop more serious disease, in which the brain or the membrane covering the brain and spinal cord swell and result in high fever, headache, neck stiffness, disorientation, tremors or convulsions, vision loss, muscle weakness or paralysis, and coma. Rarely, in severe cases, West Nile virus can be fatal or leave long-term symptoms or disabilities.

“West Nile virus has previously been found in birds and a horse in King County, and was detected in mosquitoes in neighboring Pierce County in August, so it’s not unexpected that we have a human case in King County,” said Dr. Jeff Duchin, Health Officer. “King County residents should assume local mosquitoes might carry West Nile virus.”

Preventing West Nile virus

The best way to prevent West Nile virus infection, according to King County Public Health, is to avoid mosquito bites. The species of mosquito that carries West Nile virus is most likely to bite between dusk and dawn, so be sure to wear long sleeves, long pants, and socks and use insect repellent when outside during these times.

Repellents that are registered with the EPA, such as one containing DEET or picaridin, are known to be very effective. The mosquitoes will also bite during sleep, so make sure to have screens in good repair on all windows, doors and sliders that are left open.

Mosquitoes like to lay their eggs in still or standing water. Once laid, mosquito eggs hatch into larvae and develop into adults in about two weeks in warm weather. Some species need only a few ounces of water to lay eggs. In King County, larvae tend to hatch starting in March and through October.

“Now is a good time to remove or turn over outdoor items where water could collect like buckets, wheelbarrows, , toys, and plant containers, so that mosquitoes won’t breed in them when spring comes,” said Dr. Beth Lipton, Public Health’s veterinarian. “While we will never get rid of all mosquitoes, it helps to reduce sources of mosquito breeding around your home as the mosquitoes don’t fly very far from where the larvae develop.”

Other ways to remove mosquito breeding habitat include:

  • Clean leaf-clogged gutters
  • Drain flat topped roofs
  • Dump water off of tarps and plastic sheeting
  • Cover rain barrels with mosquito screens and put lids on garbage cans
  • Dispose of old tires and junk

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