SALT LAKE CITY -- Officials from Utah's Division of Wildlife Resources say laboratory results have confirmed the illness that has been killing some of Utah's bald eagles recently is West Nile virus.
"Testing at the Utah Veterinary Diagnostic Laboratory in Logan, Utah, and the National Wildlife Health Center in Madison, Wisconsin, has definitively ruled out many other possible causes of death, including toxic chemicals or poisons, lead poisoning, bacterial infections and several other viruses, including avian influenza and avian vacuolar myelinopathy," according to a press release.
Officials aren't certain how the bald eagles contracted the virus, since mosquitoes that carry the disease are active in warmer months, but suspect it may have come from eating infected eared grebes, another species of bird that stops at the Great Salt Lake during winter migration.
Almost every year, about one percent of eared grebes that stop at the lake dies from avian cholera.
This year, however, the initial laboratory results were not as conclusive. Further testing on the grebes has led to findings consistent with what has been found in the bald eagles, the press release said.
Utah Department of Health epidemiologist JoDee Baker said the dead grebes and dead eagles do not pose a risk to humans.
“People become infected with West Nile virus after being bitten by a mosquito that carries the virus,” Baker said. “Although there are other very rare ways you can get the virus, such as receiving contaminated blood or organs from an infected person, mosquitoes are, by far, the most common method of transmission. Since the mosquitoes that transmit West Nile virus aren’t active in the winter, there’s no risk to the public’s health.”
Officials from the Division of Wildlife Resources and the Utah Department of Health urge people not to touch or handle sick birds, including eagles, and instead call the local DWR office, who will dispatch an officer or biologist to pick up the bird.
The migration of eared grebes is expected to finish soon.
“By the second week of January, almost all of the grebes will be gone,” said DWR wildlife disease coordinator Leslie McFarlane. “Even though it’s difficult to watch eagles die,” she says, “the deaths that have and still might occur won’t affect the overall health of the bald eagle population that winters in Utah or the overall population in the United States.”
As of December 31, 27 eagles had died in Utah. Of those, 21 were found dead in the wild and six died while being treated at rehabilitation centers. Five sick eagles remain at rehabilitation centers and appear to be responding well to treatments.