As severe as the consequences of an infection may be, most people who get West Nile virus will never know it.
About 80 percent of them get an asymptomatic infection, meaning they don't get sick. There's a risk, though, especially for older people or people with weakened immune systems.
"In Minnesota, we have 51 species of mosquitoes," said Dave Neitzel, a Minnesota Department of Health epidemiologist specializing in tick- and mosquito-borne diseases. Of those, he said, roughly two dozen feed primarily on people. But many are simply pesky irritants, anddon't transmit West Nile, a virus that can cause deadly encephalitis or meningitis.
Rochester sits at the eastern edge of the Culex tarsalis mosquito range. Culex tarsalis is the species that is most likely to carry and transmit West Nile to humans in Minnesota. By contrast, many of the mosquitoes in northern Minnesota — around Ely, for example — are just pests and don't carry West Nile.
Mosquito-free environment
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So where, close to home, can you get outside without becoming mosquito bait? Try Whitewater State Park.
The park has a reputation as a largely mosquito-free zone, said park intern Neil Skoog.
"It's one of the things that the park is well-known for," Skoog said.
Why is that? The park has fast-moving, fairly chilly water. Mosquitoes don't reproduce well in that kind of environment. They prefer warmer, standing pools.
Farm country tends to be a better breeding ground for mosquitoes carrying West Nile. So it's pretty easy for us to move quickly from a low-risk to a high-risk area.
Bugs carrying bugs
West Nile isn't the only mosquito concern for southeastern Minnesotans, according to Neitzel.
Another local bug, the "tree-hole mosquito," carries a virus that's similar to West Nile, except it's a greater concern for young children than older adults.
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So named because it reproduces well in and near tree stumps where water collects — to say nothing of buckets, old paint cans and other containers left outside — tree-hole mosquitoes feed during the day, as opposed to the mosquitoes carrying West Nile, which tend to feed at dawn and dusk.
A recent study showed that 1 in 12 North Dakotans had been exposed to West Nile virus. And about 1 in 150 West Nile illnesses results in severe encephalitis or meningitis.
"Those cases can be devastating to the families," Neitzel said.
About 1 in 300 to 500 mosquitoes carries the virus. So getting bitten by a mosquito doesn't necessarily mean you will get West Nile.
But the potential risks are worth considering, Neitzel said. People who are severely affected and survive often require lengthy hospital stays, and some end up with permanent cognitive or physical limitations.
