A mysterious illness that has killed upwards of 500,000 bats in the northeastern United States has now been detected in a small number of bats in Ontario.

The first cases of bats with a disease known as white-nose syndrome were found in the Bancroft-Minden area in eastern Ontario, the Ministry of Natural Resources said.

Researchers don't know exactly how the syndrome kills bats, but some researchers think the fungus acts as an irritant, causing the bat to awaken from its hibernation period early and often, which leads the bats to burn through their energy reserve and starve to death.

There is no known human health risk associated with this illness, but it has been linked to the deaths of a small number of bats in Ontario, the ministry said in a statement Friday.

People are asked to stay away from caves and abandoned mines where bats may be present, and to avoid touching bats, whether living or dead, as a small percentage carry rabies.

White-nose syndrome got its name from the smudges of white fungus that appear around the nose, mouth and wings of the affected animal.

It was first documented in Albany, N.Y., in the winter of 2006.

Since then, the syndrome has spread across nine states in the northeastern U.S. and has wiped out anywhere from 75 to 98 per cent of the over wintering bat population.

Ontario said it will continue monitoring for the syndrome until bats leave hibernation sites in May.