U.S. officials are asking people to stay out of caves in states from West Virginia to New England, where as many as 500,000 bats have died from a disease known as "white-nose syndrome."

The U.S. Fish and Wildlife Service made the request to guard against the possibility that people are unwittingly spreading the mysterious affliction when they explore multiple caves. There is no evidence that white nose is a threat to people.

Named for the sugary smudges of fungus on the noses and wings of hibernating bats, white-nose bats appear to run through their winter fat stores before spring. It was confirmed in eight states this winter from New Hampshire to West Virginia and there is evidence it may have spread to Virginia, according to wildlife service spokeswoman Diana Weaver.

Some death-count estimates run as high as 500,000 bats. Researchers worry about a mass die-off of bats, which help control the populations of insects that can damage wheat, apples and dozens of other crops.

The advisory seeking a voluntary caving moratorium also would cover states adjacent to affected states — a swath of the United States stretching from Maine down to North Carolina and west to Tennessee, Kentucky and Ohio, Weaver said.

Recreational cavers, who have enthusiastically supported past white-nose control efforts, seemed bewildered by the breadth of the request. Peter Youngbaer, white nose syndrome liaison for the National Speleological Society, said the advisory covers tens of thousands of caves and would affect everything from organized caving events to equipment sales.

"The ramifications are mind boggling, and I guess we're all just trying figure out what to do," said Youngbaer, who is based in Vermont.

"I think to great extent it will be followed, but there will be a lot of discussion and tweaking about it," he said.

Researchers suspect a fungus that thrives in cold, moist caves causes white nose and that it is spread from bat to bat. But the syndrome has spread more than 400 miles (640 kilometers) from the cluster of caves near Albany, New York, where it was first observed two winters ago.