By Laura Zuckerman
(Reuters) - An unusual wintertime outbreak of West Nile virus has killed more than two dozen bald eagles in Utah and thousands of shore birds around the Great Salt Lake, state wildlife officials said on Tuesday.
At least 27 bald eagles have died this month in the northern and central parts of Utah from the blood-borne virus, and state biologists reported that five more ailing eagles were responding to treatment at rehabilitation centers.
The eagles are believed to have contracted the disease by preying on sick or dead shore birds called eared grebes that were infected by West Nile virus, said Leslie McFarlane, Utah wildlife disease coordinator.
The water birds have died by the thousands in and around the Great Salt Lake since November. Initial testing suggested an infectious bacterial disease such as avian cholera caused the deaths, but findings released on Tuesday showed West Nile virus was the culprit, McFarlane said.
The dead birds do not pose a risk to people, Utah Health Department epidemiologist JoDee Baker said in a statement. Yet Baker urged those who find sick or dead birds to avoid handling them.
Utah wildlife specialists said bird deaths tied to West Nile virus were unusual in wintertime in Utah since mosquitoes - the primary vector - are not usually active during colder months.
West Nile virus can live for a few days in carcasses of infected birds and can be transmitted to birds of prey and scavengers that feed on them, according to the federal Centers for Disease Control and Prevention.
More than 2 million eared grebes stage at the Great Salt Lake amid a yearly winter migration from Canada and U.S. states west of the Mississippi River, according to the Cornell Lab of Ornithology in Ithaca, New York.
The water birds are expected to end their stopover in Utah and fly to the Southwestern United States and Mexico the second week of January, reducing the disease risk to bald eagles, McFarlane said.
From 750 to 1,200 bald eagles migrate to wintering grounds in Utah each year, she said.
Bald eagles, the national symbol of the United States, were removed from the federal threatened and endangered species list in 2007 after they soared back from near extinction.
(Reporting by Laura Zuckerman; editing by Steve Gorman and Matthew Lewis)