Illustration by Darren Gygi
Mosquitoes are as much a part of Minnesota summers as a trip to the cabin or a dip in one of our more than 10,000 lakes. Typically they’re just an annoyance, but as the mosquito-borne Zika virus spreads north from tropical climates—potentially causing severe brain damage to unborn children—should we be alarmed?
The key to answering the question is understanding that there are many kinds of mosquitoes, and that different types transmit different diseases. Minnesota is home to a staggering 51 mosquito species.
“The real focus [for Zika prevention] is the Aedes aegypti,” explains Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. “In many ways, this one is the most troubling. It’s the Norway rat of mosquitoes.”
Osterholm’s reference to the brown rat that has spread to every continent except Antarctica is chilling—the fuzzy creature brings diseases including fevers and hantavirus, and its proximity to people facilitates contagion.
The mosquitoes buzzing in your ear are typically a harmless species, but Aedes aegypti not only lives near people and can reproduce in receptacles of water as tiny as bottle caps, it prefers to feast on human blood (probably because it’s attracted to our scent). It seems to be particularly efficient at transmitting the Zika virus, as well. It does not, however, survive this far north, Osterholm says.
The next kind of mosquito that threatens to transmit Zika is called Aedes albopictus. While one map from the Centers for Disease Control and Prevention shows its presence edging over Minnesota’s southern border, it’s been found only in small numbers and has never gained significant traction here.
“I found the first one here at a recycling facility in town,” says Dave Neitzel, who supervises vector-borne diseases at the Minnesota Department of Health. “That’s the way these mosquitoes get here; from eggs in tires that get moved here.”
Since Neitzel’s 1991 sighting, 16 more appearances have been monitored and controlled by the Metropolitan Mosquito Control District. Any future A. albopictus hitchhiking in from elsewhere is likely to be spotted and contained, he says. And, thankfully, this mosquito hasn’t been proven to be highly effective at transmitting Zika.
That doesn’t mean Minnesotans are free from danger from mosquitoes. As many as nearly 150 cases of West Nile Virus have been reported here since 2002 (with a yearly average of more than 50), causing symptoms ranging from fatigue to neurological illness. West Nile is found in a type of mosquito that prefers farm country and feeding on birds, but sometimes feeds on people as well.
The mosquito that transmits La Crosse encephalitis, a disease with symptoms often most severe in children, is found in the southern two-thirds of Minnesota, and is most prevalent in southeast Minnesota. All told, both represent a tiny risk to Minnesotans—there’s a far less than 1 percent chance per year of an individual contracting either disease.
Yet the future risks from Zika are unknown. Early this spring, Brazilian scientists announced they had infected mosquitoes from a genus prevalent across the continental U.S. with Zika.
“But just because you infect them in the lab doesn’t mean in nature you can actually transmit a virus,” says Dr. Peter Hotez, dean of the National School of Tropical Medicine, Baylor College of Medicine. “But we haven’t closed the door on it.”
Bottom line: Don’t ease up on the mosquito repellent, especially while traveling out of state. But don’t fear the mosquito buzzing in your ear on a Minnesota night, however annoying.