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Mosquitoes and West Nile Virus

Communicable Disease, Environmental Health

Summer is almost here and outside activities beckon.  And the mosquitoes are just waiting for us!  Should we be concerned?

West Nile infection is caused by the West Nile virus and is spread to people by the bite of a mosquito infected with the virus.  The mosquito becomes infected by feeding on an infected bird.  The West Nile virus was first detected in the U.S. in 1999 and has since spread across the country.  The first human infections in Wisconsin were documented in 2002. 

About 80% of people infected by West Nile virus will not get sick.  Most of the remaining 20% will have a mild illness that can present with fever, headache, body aches, swollen lymph nodes, nausea and vomiting, or a rash on the chest, stomach, and back.  Less than 1% of infected people become seriously ill with symptoms that can include imflammation of the brain, paralysis, coma, and death.  People over the age of 50 are at greater risk of developing severe illness.  Symptoms typically occur 3-14 days after a bite by an infected mosquito.  There is no specific treatment for West Nile infection but treatment can be given to relieve symptoms.

While the risk of contracting severe illness from West Nile virus is low, the consequences for some people and their families are devastating.  Much can be done to prevent exposure and reduce risk of West Nile.

Personal protective measures include:

  • Limit time spent outside at dawn and dusk when mosquitoes are most active.
  • Wear protective clothing when outdoors.
  • Use insect repellents containing an Environmental Protection Agency registered ingredient, such as DEET, on your skin and clothes.
  • Do not use more than a 10 percent concentration of DEET on children.
  • Make sure home window and door screens are in good repair.

Reducing mosquito populations will also reduce the number of mosquito bites.  Mosquitoes lay their eggs in standing water and removing such sites from your property will help reduce the number of mosquitoes.  Steps to take are:

  • Landscape to prevent water from pooling in low-lying areas.
  • Drain water from pool covers and change water in birdbaths at least every three days.
  • Do not allow water to accumulate in ceramic pots, wheelbarrows, plastic containers.
  • Clean roof gutters and downspouts for proper drainage.
  • Trim tall grass, weeds, and vines since mosquitoes use these areas to rest during hot daylight hours. 

Birds also become sick from West Nile Virus and can die.  Oftentimes, this is the first clue that West Nile virus is present in an area and is an indication that people should take precautions to avoid mosquito bites.  State health officials have activated the statewide toll-free Dead Bird Reporting Hotline to track the virus.  Hotline staff can answer questions about dead birds and provide information on safe handling and disposal.  People should not use their bare hands to handle a dead bird.  The Hotline number is:  1-800-433-1610.

More information about West Nile virus is available at the following websites:           

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