An unprecedented wintertime outbreak of West Nile virus has killed more than two dozen bald eagles in Utah and thousands of water 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, whose symptoms included leg paralysis and tremors, are believed to have contracted the disease by preying on sick or dead water birds called eared grebes that were infected by the West Nile virus, said Leslie McFarlane, Utah wildlife disease coordinator.

 

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.

 

McFarlane said Utah had an unusually warm fall that extended the breeding season for mosquitoes to late October. But scientists may ultimately be unable to determine if grebes infected by West Nile virus migrated to Utah or if they contracted it there, she said.

 

But the epidemic in Utah may be unprecedented in North America for the masses of birds killed over a broad geographic area and for the number of bald eagles affected, said McFarlane.

 

Additional testing of grebes and eagles is underway to shed more light on the mix of factors that converged to trigger the extensive die-off and to determine how much of a risk it might pose to other types of birds.