Mosquito levels drop 50% in parts of the US, but West Nile cases hit a 22-year high

Mosquito numbers have dropped sharply in several Western and Midwestern states, with counts roughly 50% lower in places such as Minnesota and North Dakota and declines of up to 70% in Colorado.

But that apparent relief comes with a troubling catch: West Nile virus infections are at their highest point in more than two decades.

What's happening?

The main factor appears to be drought. As The Independent reports, exceptionally dry conditions across parts of the U.S. are shrinking mosquito habitat, reducing total numbers while heightening concern about mosquito-borne disease.

Minnesota resident Kahiti Stierley-Nunez, who moved from California, said the difference has been striking.

"Coming from out of state, the mosquitoes here are worse than I've ever seen them. But this year, I haven't had to put on bug spray at all this whole summer," she said.

Even with fewer mosquitoes overall, West Nile activity has intensified. The report said the U.S. has logged 143 cases, with Arizona alone reporting five deaths. Roughly half of all cases are in Arizona, and Colorado and Utah are also seeing elevated totals.

Matthew Aliota, a University of Minnesota professor who studies these viruses, explained the dynamic to The Independent: "Drought conditions can paradoxically increase West Nile virus transmission because it concentrates mosquitoes and birds (West Nile virus is a bird virus, first) around shrinking water sources, increasing transmission risk."

Why does it matter?

A quieter mosquito season may sound reassuring, but smaller insect populations do not necessarily mean a lower chance of illness. In drought-hit areas, disease risk can actually increase.

According to the Centers for Disease Control and Prevention, severe infections can cause high fever, coma, tremors, vision loss, paralysis, and inflammation in the brain and spinal cord. 

Kathleen Walker, an extension specialist and professor at the University of Arizona, told The Independent, "These are horrible, horrible symptoms, and they're the tip of the iceberg in terms of the virus activity."

Weather changes can also shift which mosquito species remain active. Some decline in dry conditions, while others continue breeding in small water sources or in environments reshaped by people, including areas affected by artificial flooding.

What's being done?

In states where West Nile cases are rising, scientists and local agencies are expanding mosquito monitoring. Communities are also trapping mosquitoes and treating standing water with insecticide to keep it from becoming a breeding site.

Researchers are also exploring tools, including ways to disrupt mosquito reproduction. The aim is to limit future swarms as warmer temperatures create more days each year that support mosquito breeding.

Utah is one place where careful monitoring remains important, because mosquito numbers can still surge under favorable conditions.

Neil Vickers, professor emeritus at the University of Utah, told The Independent, "Some surveillance traps have reported nearly 30,000 mosquitoes caught in a single night."

Robert Hancock, a Metropolitan State University Denver professor focused on mosquito behavior, summed up the challenge this way in remarks cited by The Independent: "I think that respect for mosquitoes is the most important thing that we can do because I don't think we can completely defeat them, but we can certainly continue to try."

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