Michigan State University uses weather forecast model to predict increase in West Nile Virus

DSC03907-C Researchers at Michigan State University say warm, dry weather is ideal for spreading West Nile.

The wetter the summer, the more mosquitoes you’re likely to find outside. In hot, dry summers like this there are fewer mosquitoes, but the ones there are are a greater threat. That’s because West Nile virus spreads more easily in warm weather. This summer Michigan State University has predicted an outbreak of West Nile in Michigan.

Ken Wuerfel and his pest control team at Mosquito Squad spray an insecticide on a yard on the east side of Kalamazoo. He says despite some drought this summer – business has been good because of all the rain this spring.

“When we’re wet, we’re successful. And we’ve had a great wet spring and that’s all we need. If there’s ponding rains in May -April and May – then we’re going to have a great year. If there isn’t, if it’s dry April, May, even June then our business suffers.”

Wuerfel says he doesn’t get as many calls when it’s a hot, dry summer like this one. There aren’t as many mosquitoes out there. But while some species of mosquitoes suffer in the heat, the one that carries West Nile virus thrives. It’s a hardy little mosquito called Culex pipiens and it likes urban areas with standing water. Wuerfel says they breed in everything from large retention ponds to the smallest pooling water you can find.

“If you have a water bottle and you take the cap and give it a toss and it happens to land cup side up, that little bottle cap a mosquito could – if it filled with water – lay a raft of 300 eggs.”

However, it’s not just the army of Culex mosquitoes that makes summers like this bad for West Nile. Ned Walker researches mosquito-borne diseases at Michigan State University. He says the hot weather also helps the virus spread.

“Mosquitoes are animals, they’re cold blooded. And so the warmer it is, the faster things happen. And mosquitoes get the virus infection by feeding on infected birds and then once a mosquito has gotten a blood meal from an infected bird, the virus has to grow inside the body of the mosquito. And it grows faster when it’s warmer.”

Every year Walker’s team at MSU tries to predict West Nile outbreaks based on weather patterns. He says this season closely resembles the summer of 2012. That year we saw the most deaths from West Nile in U.S. history. Out of more than five thousand cases, roughly two hundred and eighty people died.

Because the Culex mosquito likes urban areas, you’re safer in the woods than you are in the city. In fact, Walker says most people probably get West Nile in their own homes. He nicknames Culex pipiens the “Northern house mosquito” because it sneaks into houses through open doors and windows.

“Or perhaps the screens aren’t repaired properly and there’s holes in screens. Things like that that allow those mosquitoes to come in doors.”

Walker says they also bite very late at night.

“And so it’s not the typical time people put on repellant. For example, I don’t know anyone who puts on mosquito repellant right before they go to bed.”

So how do you fight such a stealthy, tough mosquito? Walker says the best way is through community-wide control.

“You can’t dump out an abandoned swimming pool and you can’t empty out thousands of street catch basins, but you can treat them. And there are communities that have adopted programs like this.”

According to the Michigan Mosquito Control Association, only four counties and about ten townships have treatment programs. Tom Putt of the association says there used to be a lot more ten years ago. But cities and towns don’t have the money for that anymore.

Ned Walker says the few municipalities that have mosquito programs are often the only ones that send MSU mosquitoes for testing. Walker says even high risk areas like Grand Rapids and Detroit don’t report.

“Unfortunately without good surveillance, we can’t make strong statements about the risk, but we do have this forecast model and that’s been reliable so far.”

Back in Kalamazoo, Ken Wuerfel of the Mosquito Squad says there are some things you can do to keep Culex mosquitoes from breeding.

“Tip standing water containers. Toss out any unwanted leaves or clippings or mulch piles or trash in the yard – because anything that can be a container for water can be a container for mosquito eggs.”

Fortunately, according to the Centers for Disease Control, 70 to 80 percent of people who contract the virus don’t have any symptoms. For more information on West Nile virus, follow the links on our website.