West Nile season in full swing

Rain brings more mosquitos, city crews are fogging

BROOKINGS – If you think there are more mosquitoes this year, you’re right. Blame the heavy rains the area had this summer, says the Brookings Street Department crew who does battle with the pests every year.

It’s also the time of the year to take precautions against West Nile Virus, because it’s a serious disease that can kill, says a state official.

South Dakota has already reported two deaths from the virus, and the virus has been detected in mosquitoes in nine South Dakota counties, including Brookings County, according to South Dakota Department of Health data released Aug. 15. Human cases have now been reported in 26 counties, including one in Brookings, and in blood donations in 11 counties.

Precautions should always be taken to prevent being bitten by a mosquito carrying the West Nile Virus.

What is WNV?

Not all mosquitoes carry West Nile Virus, said Dr. Joshua Clayton, state epidemiologist. Only the culex tarsalis mosquito carries WNV.

“The mosquito that is typically biting and bothering you during the daytime is called an Aedes mosquito – that is not a mosquito that transmits the West Nile Virus,” Clayton said. “(The culex is) most active in the evening hours – so around dusk – and can remain active for several hours, so we typically say being cautious between dusk and dawn is appropriate.”

West Nile Virus can be transmitted from mosquitoes to humans.

“Humans go on to develop either severe headache, fatigue, muscleache, fever,” Clayton said. 

“They can also progress to a more severe form called West Nile Virus neuroinvasive disease. That is where the virus had been in the person’s system, in their blood, invades the brain and into the spinal cord and can cause more severe infection in a person, leading to confusion, potentially coma and death,” Clayton said.

“Most infections tend to start off as kind of that West Nile fever: the fever, headache, body ache; and if an individual goes on to develop confusion or dizziness, a stiff neck, that’s really when you want to make sure you follow up with your physician and get appropriate testing and potentially supportive care if you’re diagnosed with West Nile Virus neuroinvasive disease,” Clayton said.

Now’s the time to be cautious because we are in WNV season, he warned.

Early August is the peak time for humans to be infected, but reports are still coming in, Clayton said.

“Individuals who have been exposed, it takes time for them to develop symptoms – anywhere from two days to 14 days … and then for that individual to seek care from their physician and be tested and that test to be reported to us,” Clayton said.

“We won’t know the exact peak of this West Nile season until the end of August or first part of September,” he added.

Last year, South Dakota recorded 73 West Nile Virus cases that included 26 of the most severe infections of WNV neuroinvasive disease.

“We ended up with 33 hospitalizations and four deaths last year,” Clayton said.

Why so many mosquitoes?

There are more mosquitoes this year, and that’s due to all the rain we’ve been getting, especially the record-setting rainfall last month, confirmed Matt Bartley, superintendent of the Brookings Street Department, and Josh McClain, head of mosquito control for the city.

The bad news is all mosquitoes bite.

The good news is most of those mosquitoes do not carry West Nile Virus and the ones that do carry WNV are at average numbers for this time of year, the two say.

McClain is one of two guys on daily mosquito patrol, checking mosquito traps around the city and standing water for the larvae the mosquitoes lay. McClain has several videos he’s shot of small bodies of water, such as what collects in ditches or low areas, and how thick the larvae are. It can take as little as a capful of water to breed hundreds of mosquitos.

On July 31, one trap contained 1,887 mosquitoes.

“Only 22 of those were culex tarsalis, the other 1,800 (plus) were floodwater mosquitoes, nuisance mosquitoes,” McClain said.

The 22 culex mosquitoes is about average, but the overall count is very high.

Bartley and McClain have been hearing from folks who have had run-ins with the larger numbers of mosquitoes we’re getting this summer, and they sympathize because they’re getting more mosquitos at their own homes, but the nuisance mosquitoes aren’t what’s worrying them.

“Our main goal is (controlling) West Nile. … We want to try to keep people healthy and try and take care of the West Nile mosquitoes and protect people from that as much as possible,” McClain said.


To help control the mosquitoes, the street department acquired a third fogger. With an extra man running another fogger, it cuts an hour off the time they spend fogging and helps them get more fog out from 9 p.m.-1 a.m. or so.

“We feel like … we’re out there at the more productive times when the mosquitos are at their peak,” McClain said.

The fog is not a magic solution, they stressed. 

“When we go out to fog, it’s not a cure-all,” Bartley said.

They don’t want to waste the fogging chemical. It costs $4,000 for a 55-gallon barrel. They use about 40 gallons in one night. Bartley does comparison shopping to stretch his budget as far as he can.

They also wait to fog until the number of culex mosquitoes reaches 10 per trap. Unfortunately, this year they were finding culex mosquitoes about a month earlier than normal, Bartley said.

“So we’re using our resources up this year a lot sooner,” Bartley said.

They conserve the fogging chemical in other ways. They make sure weather conditions are right before they even go out to fog. If there’s too much wind, it’s not worth it to go out, they said.

The fog has to contact the mosquito to kill it, so if they are under a leaf or anything else and the fog doesn’t hit it, the mosquito lives.

Some people have wondered if their area got sprayed and the guys tell them, yes, it was, but “you’re just dealing with residual mosquitoes that were maybe in your yard or in grass areas that the fog didn’t get to or maybe you’re upwind … and you don’t get the benefit of the fog blowing into your half of the block,” Bartley said.

The other thing the guys wanted to point out is they can’t spray everywhere, including private property, so if you live near an area they can’t spray, the mosquitoes hatching out of an unsprayed slough or privately-owned hayfield can come visit you.

Fogging is the best defense they’ve got, and the fight isn’t over by a long shot. McClain said they’ll be running the foggers until the weather freezes.

“Long story short, we’ve still got a rough few weeks,” Bartley said.

Protecting yourself

There are things people can do to cut down on the mosquito population; the easiest is to make sure they dump out standing water every few days. That includes pet dishes, kids’ toys, tires, bird baths, everything. Homeowners might also want to invest in some insecticide.

“Using a common chemical called Tempo to mix with water and apply that to your yard and shrubs … to help eliminate what you can back there,” Bartley said.

Watering your yard or getting rain will wash it away and eliminate its effectiveness, they warned, so it’s best to use it during a dry spell.

Using a repellant can help, too, Clayton said.

People should use one with DEET, Picaridin, oil of lemon eucalyptus, para-menthane-diol, undeanone or IR3535, he said.

“Those are repellants shown to be truly repellant to mosquitoes to help avoid getting bitten,” Clayton said, adding that those who use a home remedy do so at their own risk, as “they’ve not been fully tested like these have.”

Making sure you don’t get bit is your only protection and it’s important, he added, because some people run a higher risk of greater impact from WNV, including those 50 and older, pregnant women, organ transplant recipients, individuals with cancer, diabetes, high blood pressure and kidney disease and “those with a history of alcohol abuse,” Clayton said.

Everything helps, he said.

“It’s a big challenge, definitely, but even just helping decrease the total population of the mosquito goes a long ways to decreasing the risk for other folks,” Clayton said.

“This is an important time of the year when people need to be taking precautions and (reminded) of what some of the negative effects can be if they don’t take those precautions,” he said.

Contact Jodelle Greiner at [email protected].

SDSU photos: 

Above, Josh McClain, head of mosquito control for the city of Brookings, replaces the net on a mosquito trap in Pioneer Park on Friday. The two-man mosquito crew traps mosquitoes from mid-May to early September as part of the South Dakota Department of Health’s West Nile virus surveillance program.

Below, after the containers from Brookings mosquito traps are gathered, the mosquitoes are placed in a freezer. City employees do a rough count of the mosquitoes from each trap and then take the containers to South Dakota State University, where two undergraduate research associates sort the mosquitoes by species. The mosquitoes are then sent to the South Dakota Department of Health to determine whether they are positive for West Nile virus.


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