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The number of known dead bald eagles in northern Utah is now at 40 and five remain in wildlife rehabilitation centers with what biologists have identified as West Nile virus.

Leslie McFarlane, wildlife disease specialist with the Utah Division of Wildlife Resources (DWR), said reports of sick eagles have diminished and that could be a good thing.

"I think we may be done seeing sick birds," she said. "It seems that everything coming in now is dead so I believe that we are not actively transmitting any more."

Utah officials with the agencies overseeing wildlife, health and agriculture announced last week that the National Wildlife Health Center in Madison, Wis., had confirmed West Nile virus as the cause of the eagle deaths.

The virus had been suspected when sick and dead eagles started to show up in northern Utah in early December. But wildlife officials were reluctant to identify the mosquito-borne virus as the culprit because it has never been reported so late in the year.

It is believed that the afflicted bald eagles had consumed dead eared grebes on the Great Salt Lake. It is not known whether the grebes died from West Nile virus or served as a carrier for the disease.

Health officials say people and domestic livestock should not be at risk from this West Nile virus outbreak because the disease is almost always transmitted by a mosquito bite.

DaLyn Erickson with the Wildlife Rehabilitation Center of Northern Utah in Ogden said all four bald eagles currently at her facility continue to show signs of improvement.

A juvenile female taken to the center on Dec. 28, the 10th to arrive at the Ogden center, died late last week.

"She was just too far gone," Erickson said. "We are working to move three of the eagles into a larger area, but we are being careful to quarantine them and prevent it from spreading to other birds here."

The fourth live eagle is regaining his vision, but it is a slow process.

Erickson said only time will tell if the eagles can be released back into the wild.

"The eagles that died showed signs of heart damage," she said. "We need to watch and see how they do and see if they have the stamina and can handle physical exertion before we make that decision." Twitter: @BrettPrettyman