Experts say West Nile virus cases could increase this year, but state has a ‘scattered’ mosquito response

As of Thursday, there had been just one positive detection of West Nile virus in a human in Iowa, but Ryan Smith, an associate professor in the Entomology Department at Iowa State University, said more cases of the virus are likely on the horizon.

“This is undoubtedly the first of what has the potential for a lot of cases this year,” Smith said.

West Nile is a virus that causes West Nile fever and is most commonly transmitted through the bite of mosquitoes.

Smith — who oversees the Iowa Mosquito Surveillance Program at ISU, which has been running since the 1960s — said that historically the majority of West Nile cases are detected and reported to the State of Iowa in late August and early September.

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“We're seeing a fair amount of activity of mosquitoes at this point, probably the highest that we've ever seen up to this point,” Smith said. “So, it does ring some alarm bells for what could happen here in the next coming weeks.”

Smith said that he and his research team aren’t exactly sure why mosquito numbers have increased, but said it has to do with mosquitoes being more concentrated in certain areas of the state that become infected with the virus.

Cases of the virus so far, however, have been down slightly compared to past years, he said. In 2024, 21 Iowans were diagnosed with West Nile virus.

“West Nile viruses are endemic to the State of Iowa (and) we will see them year in and year out, so the expectation is we are always going to see some levels of activity,” Smith said. “What we don't fully understand is why some years have resulted in more cases and more infected mosquitoes than others. We're still learning.”

While there has been just one human case this year — in an adult age 41-60 in northern Iowa — the state has said “mosquitoes across Iowa are testing positive” for the virus. Some of those positive detections have been in Johnson and Black Hawk counties.

Smith said he believes one contributing factor to the mosquito activity this year could be that Iowa had a warmer winter season last year.

“Some of these mosquitoes actually hibernate and are trying to survive the wintertime, and some of these might actually even be carrying viruses with them,” Smith said. “I think there was probably a higher likelihood of their survival … they were able to hit the ground running a little bit more in the spring and cause some of the increased activity that we're seeing now.”

County-level tracking programs

Johnson County is one of the few counties in Iowa that has its own surveillance program.

Rob Thul is the environmental health manager at Johnson County Public Health, where he, along with a handful of environmental inspectors for the county, operate the program. He said his staff are the “boots on the ground” for the surveillance program.

Public health officials set mosquito traps throughout the county, and check each site three times per week to collect specimens caught in the traps.

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After each visit, the traps are reset and the specimens are sent to a lab in Ankeny, where the mosquitoes are tested for diseases.

Thul said there are a few different types of mosquito traps that the county uses, including “sticky traps” where mosquitoes are attracted to a strip of tape and stuck after flying into it.

Johnson County also uses live traps, which catch the mosquitoes in a mesh-like bag and hold them until inspectors collect them. Thul said the third type of trap the county uses is a trap that has some water inside to simulate the way mosquitoes naturally lay their eggs. A fan inside the trap draws the insects up when they enter, and traps them inside for inspectors to collect.

Thul said the program runs from May through early fall each year. This year’s program will end Oct. 3.

He said that each year, ahead of the surveillance season, the county receives a participation contract from Iowa HHS asking if Johnson County would like to participate for the upcoming year. The program is funded through HHS.

ISU partners with several other counties for its mosquito surveillance work. They include Black Hawk, Polk and Story counties.

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Dustin Hinrichs, environmental quality branch supervisor for Linn County Public Health, said the county used to have a mosquito monitoring program that ran from 1983 through 2010.

However, Hinrichs — who started his career with the county as an intern in the summers of 2000 and 2001, working on mosquito monitoring — said there was some mosquito monitoring in Linn County in the summer of 2017.

“The monitoring that year was related to targeted trapping and identification of specific types of mosquitoes related to concern for the potential spread of the Zika virus at that time,” he said, adding that the species of concern was the Aedes species that originated from Africa.

He said the formal annual program ended in 2010 because “much of the funding supporting the statewide program was cut.” That led many counties across the state — including Linn — to end their mosquito monitoring.

Stretched for funding

Smith said funding and resources is a major reason why most of Iowa’s 99 counties don’t adopt their own version of a mosquito surveillance program.

“The majority of our program is supported through the State Department of Health and Human Services, and they actually receive their money from the Center for Disease Control,” Smith said. “It ultimately comes down to government spending and funding that is influencing how much we can do.”

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Smith also said Iowa doesn’t have as many resources in place for these programs as other states do.

For example, he said Illinois has a taxpayer-funded program that combines counties into “mosquito control districts” for surveillance.

“We don't have that here in Iowa, and so it's very scattered in the response,” Smith said.

But, Hinrichs said Linn County is interested in rebooting its surveillance program in the future, “should funding be identified for this purpose and staff time permit such efforts.”

Olivia Cohen covers energy and environment for The Gazette and is a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues. She is also a contributing writer for the Ag and Water Desk, an independent journalism collaborative focusing on the Mississippi River Basin.

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Comments: olivia.cohen@thegazette.com