November 15, 2019 at 5:13 p.m.
Natural Reaction
Study results show ruffed grouse able to fend off West Nile virus
Natural Reaction
By Jacob Friede-
As part of the ruffed grouse West Nile virus surveillance project, which in addition to the state DNRs includes participation from the Ruffed Grouse Society and the Wisconsin Conservation Congress, hunters sent in blood samples and hearts from harvested grouse to be analyzed, and the results of those tests are in.
In 2018, 720 samples were collected from the three states and 235 of them came from Wisconsin. Of those 235 grouse, 68, or 29%, had antibodies to WNV in their blood.
In grouse, as in humans, antibodies that are built up to fight a disease are left behind in the blood even after the bird beats the disease.
Therefore, according to Mark Witecha, upland wildlife ecologist for the Wisconsin DNR, the numbers show that ruffed grouse are fully capable of beating WNV.
"We can't really say how many birds may have died upon exposure, but one of the main takeaways from this first year is that 29% of the birds that were harvested by hunters and sampled had been exposed in the past and had fully recovered, so that's encouraging news certainly," Witecha said.
The antibodies to WNV were found in the blood samples. The grouse hearts, however, were tested for traces of actual WNV.
"Hunters also sent us a heart and that was what we did the tissue sampling with," Witecha said. "That's looking specifically for the presence of viral RNA (Ribonucleic Acid), meaning that the virus is still present in the system of the bird."
Two of the 235 grouse had evidence of WNV in their hearts, but those grouse also had the presence of WNV antibodies in their blood, which means they were still battling the disease when harvested.
"We only had two birds that were positive," Witecha said. "Given the presence of antibodies as well in those birds would indicate that they're having an appropriate immune response and their immune system was fighting the virus off."
Grouse in Michigan and Minnesota also proved capable of fighting WNV.
In Michigan, antibodies to WNV were detected in 28 of 213 ruffed grouse, or 13%, and evidence of WNV was found in four grouse hearts.
In Minnesota, WNV antibodies were found in 34 of 273 grouse sampled, or 12%, and no hearts from that state turned up with WNV evidence.
While it was determined that some grouse successfully battled WNV, what is not known is if the exposure rate was high. It is also unclear why Wisconsin had a bit higher exposure rate than its neighbors.
The 2018 numbers are the baseline data for the scheduled three year surveillance project and only when compared to the numbers of 2019 and 2020 will their significance become more clear.
"It's definitely going to take three years worth of data to take a more comprehensive look at things like exposure rates and how they vary year to year," Witecha said.
2019 grouse samples are still being collected from hunters and they will go through the same testing process as the 2018 samples, though results should arrive quicker in year two.
Because the study is cutting edge, the lab at the Southeastern Cooperative Wildlife Disease Study in Athens, Ga., where the samples were analyzed, had to basically develop the test as they went along because you can't test, for example, crows, the same way you do grouse. The test had to be built species specific for grouse.
"They kind of know where some of the chokepoints are in the process and have fine tuned it a little bit and it shouldn't take as long to get results of the second year," Witecha said.
As far as sample size, Witecha said Wisconsin and the other states were satisfied with the amount of hunters that participated.
"Everybody was fairly happy with participation," he said. "Of course it's always beneficial to have a larger sample size so we would certainly welcome more samples, but I think we're comfortable with the level of participation that we had in the first year.
West Nile virus, which is passed through a mosquito bite, was first found in the Wisconsin grouse population in 2018 when three birds tested positive.
Witecha explained that a grouse's reaction to WNV can include lethargy and the inability to fly.
Lesions are also known to grow on an infected grouse's heart.
However, as proved early on by the ruffed grouse West Nile virus surveillance project, grouse can also have an effective and successful immune reaction and fight off WNV, and that's the big news from the first year's results.
"That to me was the single biggest takeaway from this year that the birds are being exposed and surviving," Witecha said.
For more on the ruffed grouse West Nile virus surveillance project, including information on how to participate, visit the DNR website at dnr.wi.gov and keyword search "ruffed grouse management."
Jacob Friede may be reached at [email protected] or [email protected].
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