The fungus came from caves in Europe. Scientists suspect that it was inadvertently transferred by humans, on clothing or equipment.
Bats in Europe seem to be able to live with the fungus. Scientists think many bats in Europe disappeared some time ago but others were able to develop immunity to WNS through exposure over a number of decades.
Once the fungus is established in a cave, fungal spores can transfer easily to bats, and then to other caves.