West Nile Virus activity low in Wisconsin
West Nile Virus activity has been low so far this year in Wisconsin, according to data from the Wisconsin Department of Health Services.
Through the start of August, the agency reported no WNV in humans, horses or birds.
The absence of a WNV case in a bird at this time of year is “unprecedented” since the state began tracking the disease in 2002, said Rebecca Osborn, WDHS vectorborne disease epidemiologist.
In an average year, 21 dead birds with WNV have been submitted to the agency by Aug. 1, according to WDHS data. Also, the state typically has one human case of the disease in June and two in July.
The lack of findings this year comes at a time of heightened interest and concern about WNV among the wildlife community.
The disease, spread by mosquitoes and first identified in the U.S. in 1999 and in Wisconsin in 2001, is known to affect more than 300 species of wildlife , as well as humans and horses, according to the Centers for Disease Control and Prevention. Among the species most affected are crows and jays.
At least two deaths of common loons in July in Minnesota were linked to WNV.
The disease has also been shown to cause fatalities in ruffed grouse and some wildlife officials have cited WNV as a potential cause for an unexpected downturn in grouse numbers and low percentage of juvenile birds during fall 2017 in the Upper Midwest.
“WNV clearly kills ruffed grouse and as many as 80% of grouse exposed to the virus are killed outright or might have reduced survival,” wrote Lisa Williams, PGC game birds biologist, in a September 2016 article in “Game News.”
In 2017, Wisconsin health officials documented 51 cases of WNV in humans, third-highest since 2002 and well above the average of 20.
So it's likely the virus that year was more active than average among wildlife species, too, according to researchers. However, it's unknown whether the disease could have a populationlevel effect on grouse in Wisconsin.
As a cautionary measure, the Wisconsin Natural Resources Board shortened the 2018 ruffed grouse hunting season by one month (about 20%).
Also last year, concern over the potential impact of WNV on grouse prompted state wildlife managers in Wisconsin, Michigan and Minnesota to launch a collaborative testing effort. Hunters were issued test kits and asked to submit blood, heart and feather samples from birds they killed.
The results of the testing are expected soon, according to Mark Witecha, upland bird ecologist with the Wisconsin Department of Natural Resources.
Because 2019 has been above normal for precipitation at most Wisconsin weather reporting stations, many people might expect mosquito activity and WNV activity to be up, too.
However, it's possible the Culex species of mosquitoes (the primary WNV vectors) are not higher in number this year, said Osborn.
Despite the low WNV activity noted to date, health officials cautioned it was too early to know how the year will turn out. August and September typically account for the highest number of human cases of the disease.
DNR to repeat testing
The DNR has 500 self-sampling kits for ruffed grouse hunters to use in 2019. The WNV sampling kits contain instructions and all the supplies needed to collect and ship one sample.
A leftover, unused kit from 2018 can be sent in this year for processing.
Hunters interested in participating in the study should contact their local DNR wildlife biologist. The WNV sampling kits will be available for pickup in early September.