A deadly fungal disease that has killed millions of bats in North America may be caused by a pathogen from Europe, Canadian and US researchers said on Monday.
White-nose syndrome (WNS), caused by a pathogen Geomyces destructans, was first observed to be killing bats in a cave in upstate New York in 2006, and has since killed some 6.7 million bats in the United States and Canada.
But the epidemic has not been seen in Europe, leading researchers to wonder if the disease may have been introduced from abroad by tourists who unwittingly brought the fungus from Europe into US bat caves.
A research team decided to test this idea by exposing a population of little brown bats from the Canadian province of Manitoba, where WNS has not afflicted the population, to strains originating from the United States and Germany.
One group was exposed to the US strain of the fungus, while another group was exposed to the German type.
The European type was first seen to start killing bats after 71 days, while the North American type began killing bats on day 88.
"The results of this experiment are really quite strong evidence of that invasive pathogen idea," said lead author Craig Willis, an associate professor of biology at the University of Winnipeg, in an interview with AFP.
"If anything the European version was a little bit nastier."
European bats have likely evolved some resistance to the pathogen over time, Willis explained.
North American bats did not have that protection and were left more vulnerable to the disease, which causes them to wake frequently during hibernation and subsequently waste needed body fat reserves.
In some ways, the finding is good news because it suggests that European bats are not at risk from a North American strain of the disease, though a study next year on European bats should provide more data on that matter.
However, the disease continues to wipe out bat populations - so far afflicting four Canadian provinces and 16 US states - with no end in sight.
Willis said researchers think the fungus was likely introduced by someone from abroad going into caves in New York state because the disease was first documented in an area called Howe's Caverns that receives hordes of visitors each year.
"We know the fungus can survive and persist in the environment on climbing equipment and on boots and shoes and those types of things, so it is possible that someone tracked it into this cave," he said.
Bats are valuable to the economy because they provide natural pest control for forests and farms, with some research showing they are worth as much as US$3.7 billion (S$4.6 million) per year to farmers.
The first known outbreak of WNS has been traced to a colony of bats in upstate New York, and has spread 2,000 kilometers (1,200 miles) across the United States and into Canada.
The syndrome is particularly lethal for winter colonies of species that hibernate, including little brown bats, northern long-eared bats and the endangered Indiana bat, according to the United States Geological Survey.