West Nile cases see significant drop in South Dakota

Published: Sep. 23, 2020 at 6:50 PM CDT
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ABERDEEN, S.D. (Dakota News Now) - Cases of West Nile are usually a major health focus for the state of South Dakota in the Summer and Fall months. But cases the past couple of years have decreased significantly, and city and county officials are still trying to figure out why.

According to the South Dakota Department of Health, so far there have been five confirmed cases of the virus in 2020. That’s half of last year’s total of 10. But both pale in comparison to 2018, which saw 169 confirmed cases in the state, including four deaths.

Even with the ongoing drought in much of the state, mosquito populations remain at average sizes. It’s a questions that Aberdeen Parks Superintendent Tyler Bierman and his staff are wondering as well, trying to figure out why cases are dropping even with consistent mosquito populations.

“The last couple of years, and this year included, the numbers and trap counts have been pretty much the same, as average as they always are. You know, even the Culex numbers, last year and this year, Culex numbers have been as high as they were in 2017, 2018.” Bierman said.

Snow melt and rain fall in the Spring and early Summer months allowed mosquito populations to establish, and survive in the drier months. Chris Hemen, the Brown County Weed and Pest Control Supervisor, said that even with the lack of rain this Summer, mosquitoes can still find welcoming places to live and breed.

“Rain gutters, tires, you know garbage lying around like that where you can get a little bit of rain, and it takes a long time for that water to evaporate. That’s really all they need.” Hemen said.

Both Bierman and Hemen say they don’t know why case numbers have been dropping the past couple of years, but say they will continue to spray and check mosquito number regularly.

However that doesn’t mean the risk of getting the virus is gone. The Department of Health says mosquitoes that carry the virus can be active into the Fall season, even in drier years.

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