SALT LAKE CITY -- The mystery illness that has killed 27 bald eagles in Utah this month appears to be West Nile Virus, state officials said Tuesday.
The Utah Division of Wildlife Resources said in a statement that laboratory tests done on some of the first birds found indicate they died from West Nile Virus.
Since Dec. 1, officials have found the birds in northern and central Utah. All were either dead or were ill and later died during treatment.
The eagles displayed similar symptoms, including head tremors, signs of seizures, weakness in legs and feet and a paralysis of the bird's wings.
Beyond the 27 that have died, officials said five eagles were being treated at a wildlife rehabilitation centre Tuesday. They appeared to be responding well to treatment, officials said.
Utah wildlife officials aren't sure how the eagles caught the virus, but they suspect the birds contracted it by eating Eared Grebes that were infected with the virus and died recently.
West Nile Virus, which is spread by mosquitoes, usually infects eagles and other birds during warmer months.
Mark Hadley, a Utah Division of Wildlife Resources spokesman, said the grebes, a duck-like aquatic bird, start arriving in Utah in October, when mosquitoes are still active.
"It's possible that those grebes got bit by mosquitoes after they got here when they arrived in the fall, and it just took a while for them to die."
The bald eagles began arriving in November and appeared to have died relatively quickly once they contracted the virus, Hadley said.
About 750 to 1,200 bald eagles begin migrating to Utah each November and stay until March, officials said.
During those winter months, the eagles get most of their food by eating dead animals, such as grebes.
Leslie McFarlane, a wildlife disease co-ordinator with DWR, said in a statement that there's still a chance a few more eagles could die, but because the migration period for grebes is almost over, it's likely that the risk to eagles will soon drop.
The birds do not pose a risk to human health but people should not handle eagles if they find them, wildlife officials said.
Hadley said that in the 17 years he's been with DWR, he has never seen this many eagles die off, particularly in such a short period of time.