Even though summer feels as if it's winding up, there's a full month of it ahead, and this is the time of year when West Nile virus can come on a bit stronger.

Lake states have an abundance of mosquitoes, but residents in many states need to keep their guard up. Nineteen cases of WNV-related illness, including two deaths, have already been reported to the Minnesota Department of Health. That's ahead of numbers reported at this time in previous years.

 “Warmer than normal weather this summer has sped up the development of WNV in mosquitoes,” says David Neitzel, an MDH epidemiologist specializing in diseases carried by mosquitoes and ticks.  “We’ve already seen WNV activity in mosquitoes and birds weeks earlier than expected.”  Recent rainfall also could lead to an August peak in numbers of Culex tarsalis mosquitoes-- the primary carrier of WNV in Minnesota and some other states.

This summer’s hot and dry weather has kept other pest mosquito numbers down. People are not being bitten as often, so they may believe their disease risk is non-existent.  However, Culex tarsalis mosquitoes and WNV thrive in this type of weather.  “You may not have noticed many mosquitoes when you’ve been out at dusk this year, but unfortunately the few that are out there may be carrying WNV,” says Neitzel.

“The Culex tarsalis mosquito prefers open, agricultural areas," he adds. Consequently, farmers and other outdoor workers are vulnerable. It is therefore important ag residents take simple precautions to prevent mosquito bites. 

To reduce your risk of being bitten by mosquitoes:

  • Use a mosquito repellent when outside. The most effective repellents contain the active ingredients DEET (up to 30 percent), picaridin or oil lemon of eucalyptus.
  • Minimize outdoor activities at dusk or dawn, when the mosquitoes that transmit WNV are most actively feeding.
  • Wear long-sleeve shirts and long pants if you have to spend time in an area where mosquitoes are biting.
  • Eliminate mosquito breeding sites on and around your property including items such as old tires, buckets, clogged rain gutters, cans and other containers that can hold small amounts of water. Change water in birdbaths and livestock troughs at least weekly. 

People are at risk for WNV until frost occurs.  Freezing conditions kill mosquitoes or force them to find protected locations to over-winter.  Thus, it is important to keep preventing mosquito bites into fall. 

Of those who become infected with WNV, most people will have no or display only mild symptoms.  Approximately one out of 150 people who become infected will develop encephalitis or other severe forms of the disease.  Symptoms usually show up 3 to 15 days after being bitten.  They can include headache, high fever, rash, muscle weakness, stiff neck, disorientation, convulsions, paralysis and coma.  Severe cases tend to occur most often in the elderly. 

People who have questions about West Nile virus can call MDH at (651) 201-5414 between 8 a.m. and 4:30 p.m. Monday through Friday.

Source: Minnesota Department of Health