West Nile virus linked to deaths of 27 bald eagles in Utah

After ruling out a number of possible culprits– avian cholera, erysipelas, lead poisoning and a number of other toxins and chemicals, officials with the Utah Division of Wildlife Resources (DWR) report that laboratory analysis confirms that West Nile virus (WNV) killed the bald eagles that have died in Utah over the past few weeks, according to a DWR news release Tuesday.

Bald Eagle
Public domain image/Ken Thomas

Testing was performed at the Utah Veterinary Diagnostic Laboratory in Logan, Utah, and the National Wildlife Health Center in Madison, Wisconsin, which ruled out other causes and confirmed WNV.

However, another question remains. It’s not clear how the eagles contracted the virus as the disease typically affects birds (including eagles) during warmer months, when mosquitoes that carry the disease are active.

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They think the birds might have contracted the virus after eating infected eared grebes that died recently on Great Salt Lake.

Leslie McFarlane, wildlife disease coordinator for the Utah Division of Wildlife Resources (DWR), says more than 2 million eared grebes stop at Great Salt Lake during their winter migration. Almost every year, about one percent of the population that visits the lake dies from a bacterial disease called avian cholera.

“Every time grebes die,” she says, “we send some of the dead birds to a laboratory for testing. Usually, avian cholera jumps out as the cause of death. This year, though, the initial laboratory results were not as conclusive. That led us to believe that something else might have killed the grebes this year.”

In the winter, bald eagles obtain most of their food by eating dead animals. Since all of the eagles that have died have been within flying distance of the lake, McFarlane thinks the eagles might have contracted West Nile virus after eating grebes that died at the lake from the disease.

Health officials in Utah say there is no human public health concern associated with the eagle die off, “People become infected with West Nile virus after being bitten by a mosquito that carries the virus,” JoDee Baker, epidemiologist with the Utah Department of Health says. “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.”

While the eagles don’t pose a risk to public health, both Baker and McFarlane encourage you to not touch or handle sick or dead birds, including eagles.

On the morning of Dec. 31, the number of eagles that had died in Utah stood at 27 birds. Twenty-one of those birds were found dead in the wild. Six additional birds died while being treated at rehabilitation centers.

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