A Fungus Devastated North American Bats. A New Species Could Deliver a Killer Blow.

New York Times

7 days ago

In the winter of 2006, biologists in New York State got a gruesome surprise. As they surveyed colonies of hibernating bats, they discovered heaps of dead animals on the floors of caves and abandoned mines.
The culprit was a fungus new to science. It caused white-nose disease, named for the fuzzy pale tendrils that sprouted from the nostrils of its victims. (The disease was originally known as white-nose syndrome, but was renamed in recent years.) The fungus, Pseudogymnoascus destructans, or P. destructans, has spread from New York to 40 states and nine Canadian provinces.
'This is the most dramatic wildlife mortality event that's ever been documented from a pathogen,' said DeeAnn Reeder, a disease ecologist at Bucknell University. 'Millions and millions and millions of animals have died.'
In recent years, bat experts have gained some guarded optimism. They have found ways to protect bats from white-nose disease and to help infected animals survive. But a new study published on Wednesday raised the possibility that North American bats could get slammed by a second wave of white-nose disease.
An extensive genetic survey has found that Pseudogymnoascus destructans is actually two species native to Europe and Asia. Only one has reached North America. If the second one is introduced to the continent, it could start another devastating epidemic.
'It's like a reboot,' said Dr. Reeder, who was not involved in the study. 'I think it's terrifying, honestly.'
The leader of the new study, Sébastien Puechmaille of the University of Montpellier, was still a graduate student studying bat conservation 17 years ago when his American colleagues at scientific conferences told him about a new plague.
'We'd be talking, and then they said, 'Yeah, we have these bats that are dying with something growing on them, possibly a fungus,'' Dr. Puechmaille recalled.
Dr. Puechmaille and his European colleagues knew that European bats sometimes grew fuzzy white patches on their noses, too. But their infections weren't lethal, so researchers paid little attention to them. 'And then, very quickly, we found out that it was similar to what was found in North America,' Dr. Puechmaille said.
That discovery led Dr. Puechmaille to dedicate his career to understanding the new fungus. He helped chart its range across Europe and as far east as South Korea. Yet nowhere in Europe or Asia did P. destructans cause mass die-offs like it did in North America.
Dr. Puechmaille and his colleagues worked out the reason for this sharp contrast. The fungus originally evolved in Europe and Asia, where it developed a peaceful coexistence with bats over millions of years.
The fungus only grows at the cool temperatures in a bat's hibernating body. It causes no lasting harm to the animals, which warm up in the spring and shed the fungus. When the bats leave their caves, they leave behind fungal spores that can infect new hosts the next winter.
'When the bat comes back in autumn, if it touches the wall with its wings or ears or anything else, then some spores get onto it, and the cycle starts again,' Dr. Puechmaille said.
When P. destructans suddenly appeared in North America in the early 2000s, the bats there were ill-equipped to handle the new disease. As their immune systems struggled against the fungus, they woke up often during the winter and burned up their fat reserves. By the spring, many infected bats had starved to death.
To reconstruct the deep history of P. destructans, Dr. Puechmaille enlisted a network of hundreds of volunteers to amass a collection of fungal samples. He and his colleagues then sequenced the DNA of more than 5,400 samples for clues into how the fungus evolved, and how it managed to reach North America.
All the samples of P. destructans that scientists have studied in North America are nearly identical clones. They all must have descended from a single spore introduced to the continent, presumably not long before the discovery of the disease in 2006 in New York.
Until now, scientists had little idea where exactly the North American fungus came from across the range of P. destructans, which stretches more than 5,000 miles. 'We had nothing to pin it down,' Dr. Puechmaille said.
In their new study, Dr. Puechmaille and his colleagues discovered that the North American fungi closely match samples collected from bats hibernating in caves in the Podillia region of Ukraine. The analysis zeroed in on an 18-square-mile area as the most likely origin of the spore that started the North American epidemic.
After the fall of the Soviet Union in 1991, American spelunkers made contact with their Ukrainian counterparts and started exploring Podillia's maze of caves. Dr. Puechmaille speculated that spore-riddled mud could have stuck to a caver's gear and survived a trip back to the United States. That caver may have then unwittingly transported the spore to a New York cave on a boot or a rope, setting off a new epidemic.
'We do not want to blame people,' Dr. Puechmaille said. 'The only thing we wanted to do was to find evidence that there was definitely a movement between these regions.'
The study not only clarifies the origin of the white-nose epidemic in North America but also raises serious concerns about a future outbreak.
Dr. Puechmaille discovered that the fungal samples belonged to two genetically distinct groups. That means P. destructans is not one species, as originally thought, but two, called Pd-1 and Pd-2 for the time being.
The two species split from a common ancestor roughly a million years ago. The range of Pd-1 extends throughout Europe as far east as the Ural Mountains in Russia. Pd-2 is less common in Europe, but also extends into Asia. The two species of fungi seem to specialize on certain species of bats, although Dr. Puechmaille's team has discovered some individual bats in Europe infected with both Pd-1 and Pd-2.
The North American epidemic was caused solely by Pd-1. If Pd-2 reaches North America, Dr. Puechmaille warns, it could cause trouble as well. Bat species hit hard by Pd-1 might get pushed to extinction, and species that managed to resist Pd-1 could succumb to Pd-2.
'It's really important for conservation that we should set up some policies to prevent this second fungal pathogen from being transported to other continents, including North America,' Dr. Puechmaille said. People should not move cave equipment between countries, he said, and they should disinfect it between expeditions.
'A single spore is enough,' he warned.