Scouting cornfields now might net you a different problem than the insects you might have anticipated encountering. An Iowa State University researcher says there are “very high levels” of West Nile virus (WNV) trending in Iowa and other Midwestern states currently.
“This week had the highest observed WNV activity at this point in the summer observed in over 20 years. This trend is of serious concern for the next eight weeks when WNV transmission risks are the highest,” writes Erin Hodgson, ISU Extension entomologist specialist.
To date in 2025, there have been 219 cases of WNV reported in 29 states. In 2024, there was a total of 1,466 cases of WNV reported in the U.S., according to Vector Disease Control International.
In Iowa, data is generated from ongoing mosquito surveillance efforts coordinated by Ryan Smith, ISU associate professor and entomologist. Smith has implemented an interdisciplinary approach to examine mosquito immunity and mosquito-borne disease transmission.
Leading Cause Of Mosquito-Borne Disease
West Nile virus is transmitted through the bite of a Culex mosquito, commonly called a house mosquito. It typically picks up the virus by feeding on an infected bird. West Nile virus is the leading cause of mosquito-borne disease in the continental United States.
In general, people do not spread the infection.
There are no vaccines to prevent or medicines to treat West Nile in people. Fortunately, most people infected with the virus do not feel sick, according to the Centers for Disease Control and Prevention (CDC). About 20% of people who contract the disease will experience mild symptoms like fever, headache, and body aches.
In a small percentage of cases, the virus can cause serious neuroinvasive disease issues, such as encephalitis or meningitis, which can be severe and even fatal, the CDC reports.
People older than 60 and those with weakened immune systems are at highest risk for severe illness.
The CDC offers an interactive site where you can view and track the total number of human infections of WNV reported on a county-by-county basis. See current results in your county here.
Implement The Three Rs
To prevent mosquito bites, the CDC encourages people to practice the ‘Three Rs’:
REDUCE - make sure doors and windows have tight-fitting screens. Repair or replace screens that have tears or other openings. Try to keep doors and windows shut. Eliminate, or refresh each week, all sources of standing water where mosquitoes can breed, including water in bird baths, ponds, flowerpots, wading pools, old tires, and any other containers.
REPEL - when outdoors, wear shoes and socks, long pants and a light-colored, long-sleeved shirt, and apply an EPA-registered insect repellent that contains DEET, picaridin, oil of lemon eucalyptus, IR 3535, para-menthane-diol (PMD), or 2-undecanone according to label instructions. Consult a physician before using repellents on infants.
REPORT – report locations where you see water sitting stagnant for more than a week such as roadside ditches, flooded yards, and similar locations that may produce mosquitoes. Your local health department or city government may be able to add larvicide to the water, which will kill any mosquito larvae.
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