Officials with the Utah Division of Wildlife Resources were concerned by the deaths in recent weeks. Many eagles were found dead in the wild, and six died while being treated in rehabilitation centers, officials said.

The department tested the birds and ruled out several other possible causes of death, including toxic chemicals, poisons, bacterial infections and viruses. Officials believe that the birds contracted the virus by eating infected waterfowl, called eared grebes, that died in the Great Salt Lake.

The virus is rare in the winter because it usually spreads through mosquitoes, which are more active during the warmer months, officials said.

People who live near the lake should not be concerned about getting the virus, said JoDee Baker, an epidemiologist with the Utah Department of Health.

“Since the mosquitoes that transmit West Nile virus aren’t active in the winter, there’s no risk to the public’s health,” Baker said in a statement.

Five sick eagles were still being treated at rehabilitation centers earlier this week. The virus could infect more birds, officials said, but the risk should lessen in the coming weeks because eared grebes leave the region by mid-January as part of their normal migration.

Utah has between 750 and 1,200 bald eagles each winter.

“Even though it’s difficult to watch eagles die, the deaths that have and still might occur won’t affect the overall health of the bald eagle population that winters in Utah or the overall population in the United States,” said Leslie McFarlane, the wildlife disease coordinator for the Utah Division of Wildlife Resources.