Two white-tailed deer previously identified as CWD positive during Arkansas modern gun deer season opener have tested negative for chronic wasting disease during confirmation tests.
One of Marion County’s two CWD-positive samples and the lone positive sample in Yell County from those taken during opening weekend of the 2016-17 deer season have been reversed, following immunohistochemistry (IHC) tests sent to verify the initial findings.
“We submit samples to a laboratory that conducts the ELISA (enzyme-linked immunosorbent assay) method as a screening test. This ELISA test has the ability to process a large number of samples at a quick rate, and can produce a specificity exceeding 99 percent,” said Cory Gray, deer program coordinator for the AGFC.
“But, in some cases, the confidence level in a sample result can be low. In those situations, we follow up the ELISA test with the IHC test to ensure an accurate test result. In addition, anytime we receive a CWD-positive suspect in a new county, we send an additional sample collected from that animal to run the IHC test. The IHC is extremely accurate and reliable – the gold standard in regard to CWD testing – but the downside is that it may take weeks before sample results are received versus a few days with ELISA.”
In two of the resubmitted samples, the IHC test came back clean. During the AGFC’s first detection of the disease in February, additional samples also were sent for confirmation testing to ensure accurate results before the AGFC’s first announcement to the public.
The identification of these false positives will help the AGFC’s future detection of the disease, and any samples that indicate CWD at a low threshold in ELISA testing will be resubmitted for further analysis.
Currently, the AGFC has one additional sample from Searcy County waiting for IHC testing as a follow-up from the initial ELISA results.
The reversal of the Yell County sample results offers some relief from biologists’ fears that the disease had crossed the Arkansas River.
“The river really doesn’t pose a huge barrier because deer can swim pretty well,” Gray said. “But anything that can slow the spread of the disease a little more is always welcome. Research in other states suggests that rivers, roads and ridges may serve as barriers, hindering the spread of the disease.”
The AGFC has collected samples from 1,592 road-killed deer, 298 deer reported as sick by the public and 1,136 samples from hunter-harvested animals. To date, 150 white-tailed deer and six elk have been confirmed with CWD in Arkansas.
“We do have 394 samples taken by cooperating taxidermists that we are still waiting on results from,” Gray said. “And the Missouri Department of Conservation has taken 47 samples from Arkansas deer that were transported across the state line by Missouri hunters.”