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Summertime West Nile virus threat difficult to predict

North Dakota case numbers rise and fall over time

West Nile Virus case numbers in North Dakota vary from year to year. Source: North Dakota Department of Health

FARGO — The return of summer means the return of mosquitoes and with them the potential spread of West Nile virus, a threat that first appeared in the state nearly two decades ago.

West Nile became reportable in the state in 2002 and since then 24 people have died from the illness caused by the virus, with the last North Dakota West Nile death reported in 2018, according to Michelle Dethloff, infectious diseases and epidemiology director for the North Dakota Department of Health, which has a page on its website devoted to West Nile virus .

The disease is spread by mosquitoes and mostly affects birds.

People infected with the virus usually don't display symptoms, but those who do typically suffer headaches, fever and body aches. A small number who show symptoms become seriously ill, with swelling of the brain or even death occurring.


North Dakota saw six West Nile Cases in 2020. Source: North Dakota Department of Health

Since 2002, West Nile case numbers in the state have varied from year to year, with the high occurring in 2007, when 369 cases were reported, 49 of those in Cass County.

From 2009 through 2011, the state reported less than 10 cases each year, but the numbers jumped to 89 in 2012 and then to 127 cases in 2013, with 17 of those in Cass County.

In 2018, statewide cases numbered 204, with 16 of those in Cass County.

2019 saw the statewide number of West Nile cases drop to nine. In 2020 the number fell to six.

"We've had years where we had very few cases and then others where it's been kind of moderate. Then, like in 2018, where we had a larger number of cases," said Dethloff, who noted that predicting how bad West Nile virus numbers will be in a given summer is difficult to do.

She said a dry summer doesn't necessarily translate to fewer mosquitoes and less West Nile transmission and she cited 2007, a dry year with 369 West Nile cases.

"It doesn't always correlate with wet weather. We don't know what's going to happen," Dethloff said.


When it comes to preventing infection by West Nile, Dethloff said what individuals do to protect themselves is the most important line of defense.

"You can have the most fantastic mosquito control program, but you know you're not going to get every mosquito," she said.
"The personal protection is the most important," Dethloff added, noting that putting repellent on your skin, staying indoors during peak mosquito hours and keeping grass and shrubbery trimmed all help to thwart disease transmission.

And while steps like mosquito spraying may not be a cure-all for West Nile transmission, such programs do have a place in the overall effort, according to Dethloff.

"It might be beneficial to do some control," she said, noting that can mean spraying for adult mosquitos or treating standing water where insects breed.

But not everyone is convinced aerial spraying is the way to go in combating West Nile virus.

Ron Miller, a retired pediatrician from Fargo who practiced medicine in local hospitals for 40 years, opposes aerial spraying for mosquitos, at least in the Fargo-Moorhead area where he said the human population is too low for aerial spraying to be effective at controlling the spread of West Nile virus.

Miller said in addition to a densely populated area, the other criteria necessary for aerial spraying to be effective against the West Nile virus is that an actual epidemic of the virus must exist, adding that he believes the low case numbers in North Dakota in recent years do not meet the threshold.

According to Miller, the best defense against mosquitos and therefore the West Nile virus are the personal steps people can take to protect themselves.


He said he has a cabin in Minnesota where he likes to go fishing at night, but he doesn't wet a line unless he has applied DEET to his skin and he is wearing clothing impregnated with mosquito repellent.

"I'll continue to do that into the summer, when mosquitoes are rampant," Miller said.

The subject of aerial spraying for mosquitoes came under intense public debate last August, when large numbers of dead monarch butterflies appeared around the area following an aerial spraying.

In the wake of that debate, Moorhead officials recently decided aerial spraying may remain an option this summer, but a committee of city residents and experts from around the nation are working to develop a plan for when to do aerial as well as truck spraying.

The panel has plans to meet weekly, with a detailed report expected by late June that will help Moorhead officials decide whether to keep aerial spraying as an option this year.

Aerial spraying is usually done in late July and August.

Ben Prather, the director of Cass County Vector Control, said that in addition to limiting disease, controlling mosquitoes is about reducing the nuisance factor when it comes to the public's ability to enjoy the outdoors during the summer.

"It is demanded. It's part of our charge as a mosquito control district," Prather said.

I'm a reporter and a photographer and sometimes I create videos to go with my stories.

I graduated from Minnesota State University Moorhead and in my time with The Forum I have covered a number of beats, from cops and courts to business and education.

I've also written about UFOs, ghosts, dinosaur bones and the planet Pluto.

You may reach me by phone at 701-241-5555, or by email at dolson@forumcomm.com
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