LOS ANGELES _ Federal researchers say an infectious and lethal cold-loving fungus sweeping through parts of North America and Canada has killed millions more bats over the last five years than previously estimated.

The rapidly spreading fungus responsible for white-nose syndrome is now believed to have killed 5.7 million to 6.7 million bats, a count several times higher than earlier estimates, across 16 states as far west as Oklahoma.

The fungus, which scientists know as Geomyces destructans, seems to prefer the 25 species of hibernating bats. But each of the 45 species of bats in the United States and Canada may be susceptible, wildlife biologists say.

Estimating the number of bat deaths posed a challenge for biologists because establishing numbers of once common species had not been a primary focus of seasonal population counts. But with mortality rates reaching up to 100 percent at some sites, a team of 140 researchers in the United States and Canada recently coordinated their survey strategies to come up with a consistent estimate, said Jeremy Coleman, national white-nose syndrome coordinator for the U.S. Fish and Wildlife service.

The higher number shows the gravity of the problem, Coleman said in an interview. "We still don't know what the cascading effects will be in the environment to our ecosystems.

"This much is certain: Bats have such low reproductive rates that it will likely take multiple human generations to get bat populations back up to the numbers they were just five years ago," Coleman said.

The disease has killed mostly little brown bats _ one of the most common mammals in North America _ which have lost an estimated 20 percent of their population in the northeastern United States.

"We are just beginning our winter surveys for this year and we expect to find that the disease has spread to additional states," said Ann Froschaur, a spokeswoman for the U.S. Fish and Wildlife Service.

White-nose syndrome can be transmitted between animals through direct contact. It gets its name from the powdery, white substance that appears around muzzles, ears and wings of affected bats.

Bats with white-nose syndrome exhibit unusual behavior during cold winter months, including flying outside during the day and clustering near the entrances of caves and mines where they hibernate. Bats have been found sick and dying in unprecedented numbers near these hibernacula during a portion of the year when there are no insects to eat.

Researchers are racing to find methods of managing the pathogen, including possible vaccination campaigns, and to manipulate the environment that brings it together with bats _ the chilly galleries of caves.