Environment & Science
9:00 am
Thu August 9, 2012

Hot, dry summer favors mosquitoes that carry West Nile virus

You can listen to the Environment Report broadcast for Thursday August 9th. An expanded version of the West Nile story appears below.

Maybe you’ve noticed you haven’t been swatting a lot of mosquitoes this summer. 

“It’s been a strangely quiet year for nuisance mosquitoes in particular.”

Michael Kaufman is a mosquito expert and an associate professor at Michigan State University. 

“Most people think all mosquitoes are a nuisance and I guess I’d have to agree with that. But the ones most people complain about come out in large numbers after rain events or spring snow melts and things like that.”

Think of nuisance mosquitoes as the kind that attack you in swarms.

Kaufman says it’s been so dry that we haven’t had the usual bursts of mosquitoes that you get after a big rain. 

But he says ironically, our hot, dry summer has been ideal for the species of mosquitoes that carry West Nile virus.  The species Culex pipiens is the one experts are most concerned about... and those guys like it when it’s hot.

“The Culex breed in areas that don’t necessarily need that much water. A really good source of them for their larval development is what we call catch basins or parts of storm sewer drainage systems.”

Kaufman says they also like standing water in bird baths and kiddie pools.

He says because it’s been so hot for so long... we’re seeing cases of West Nile virus pop up in humans and animals a few weeks earlier than normal. 

Erik Foster is a medical entomologist with the Michigan Department of Community Health. He says so far this year in Michigan, there have been four confirmed cases of West Nile virus in humans.  But he says it’s really difficult to predict what will happen with the virus each year.

“You know, if things continue the way they are right now, we may have a bad year for West Nile virus.”

Foster says you can get infected with West Nile virus without having any symptoms.  You might also get just a mild flu-like illness.  But he says some people can become seriously ill.

“You start having neurologic involvement, you can start getting weakness in the limbs, you can start having changes in behavior, extreme headache and neck pain, and that’s definitely when you want to go see your doctor and get treated.”

Foster says people over age 50 are more likely to develop serious illness from West Nile virus.

People have been getting sick with West Nile virus since 2002 in Michigan, but Foster says no one knows how much of the population might have immunity by now.

“We’re not sure there is long-standing immunity after you are bitten by an infected mosquito. But you can’t really count on being immune unless you know for sure you were infected with West Nile virus previously.”

So he says... the best thing to do is to avoid getting bitten. There are easy things you can do, like drain any standing water around your house and make sure your window screens are in good shape. He also recommends using bug repellant when you’re outside.

Here are some additional guidelines from Michigan.gov's Emerging Disease Issues site:

  • Reduce time outdoors, especially at dusk, during mosquito seasons
  • Wear light weight long sleeves and long pants if you are outdoors
  • If outdoors, apply insect repellent exposed skin or clothing that contains the active ingredient, DEET. Repellents containing Picaridin or Oil of Lemon Eucalyptus have recently become EPA approved and recommended for use by CDC.  (Be sure to follow the manufacturer's instructions).  For more information on mosquito repellents, click here.
  • Maintain window and door screens to keep mosquitoes out of buildings
  • Empty standing water from flower pot bases, pet bowls, clogged rain gutters, swimming pool covers, discarded tires, buckets, barrels, cans, etc.