New fungal pathogen threatens bats

[Press release] - Published on May 28, 2025 in Press Corner, Science-Society

An international team led by scientists from the University of Montpellier, in collaboration with scientists from the CNRS and partners in Germany, Bulgaria, Finland, and Ukraine, analyzed a colossal number of samples of the fungus responsible for the largest mammal mortality ever documented. This major work, supported by more than 360 volunteers, was published in the prestigious journal Nature on May 28, 2025. It revolutionizes the current understanding of white-nose disease, revealing unprecedented insights into the identity and diversity of the pathogens involved.

White-nose disease, a disease we thought we knew well!

Diseases don't just affect humans: in 2006-2007, a massive, unexplained bat die-off was observed in a cave in New York State. The animals had a white powder on their snouts, caused by a then-unknown fungus, Pseudogymnoascus destructans . This fungal disease, called "white-nose disease," quickly spread across North America, decimating hibernating populations with annual mortality rates exceeding 90%, and causing the deaths of several million bats. Researchers discovered that this fungus originated in Eurasia, where it coexists with local bats without causing mass mortalities. Its accidental introduction to North America triggered one of the most devastating epidemics ever documented in wild mammals.

For nearly 20 years, the story of this pathogen was believed to be relatively simple: a single agent, an identified geographic origin (Europe), and well-established mechanisms. But new genetic data reveal a far more complex story, challenging our certainties about the origin, diversity, and evolutionary dynamics of this pathogenic fungus.

Not one, but two species of fungi cause the disease!

Until recently, Pseudogymnoascus destructans was considered the sole causative agent of white-nose disease. However, this study, based on the analysis of an impressive number of samples (5,479) from 27 countries and three continents, highlights the existence of two distinct species of fungi capable of causing the disease, although only one of the two species has been introduced to North America. This discovery challenges the idea of a single pathogen and reveals the complexity of disease dynamics. It thus opens new perspectives on the evolution of virulence and on how these pathogens interact with their hosts according to geographical contexts.

" We thought we knew our enemy, but today we discover that it is twofold, and potentially more complex than we imagined ," summarizes Nicola Fischer, first author of the work, who completed her doctorate on the subject between the University of Greifswald in Germany and the University of Montpellier.

A significant risk to bat conservation

The discovery of a second pathogenic fungus, capable of causing white-nose disease and with a different host specialization, poses a considerable risk to bat conservation. Although the second species is currently absent from North America, its introduction could threaten bat species not yet affected by the first. Moreover, even bat species that are beginning to recover from exposure to the first pathogen could face new challenges if the second were to spread. This situation is reminiscent of the chytrid fungi that devastated amphibian populations, where the emergence of a second, more specialized species after a first generalist species had devastating effects. In the case of the second species of P. destructans , there is still room for preventive action to strengthen global biosecurity and limit the risks associated with this new threat.

In Eurasia, both fungal species are already present, but fungal populations are highly geographically structured. The main risk lies in the convergence, often induced by human activities, of previously isolated populations. This could promote genetic recombination within the same species, a well-known mechanism among fungi for generating new, sometimes more virulent, variants. Such an emergence would represent a serious threat to Eurasian bats, even though they appear unaffected so far.

The origin of the introduction to North America finally elucidated

Through genetic analysis of more than 5,400 samples collected across Eurasia and North America, the study identifies for the first time with precision the region of origin of the lineage responsible for the North American outbreak of white-nose disease: the Podillia region of Ukraine. This area, home to some of the world's largest cave systems, has been a popular destination for international, particularly North American, cavers since the end of the Soviet Union. The results suggest that the accidental introduction of the fungus into North America, likely via exchanges with cave explorers from New York State, where the disease was first detected, stemmed from a single event. This work ends nearly two decades of speculation about the origin of white-nose disease across the Atlantic and vividly illustrates the impact a single translocation event can have on wildlife.

Caving and biosecurity: a crucial issue for disease prevention

This discovery highlights the major risks posed by caving activities for the dispersal of pathogens, and underlines the urgent need for a better understanding of “biological pollution” linked to human travel. Preventing the inadvertent transport of pathogenic fungi such as Pseudogymnoascus destructans must become a priority in conservation and health management strategies, both for wildlife and humans. The systematic and rigorous cleaning of caving equipment during trips is essential: studies show that it drastically reduces the presence of viable spores and thus limits the spread of the fungus that causes white-nose disease.

Volunteers at the heart of scientific discovery

This study would not have been possible without an extraordinary mobilization. Thanks to a collective data collection effort across the northern hemisphere, involving several hundred volunteers—mostly chiropterologists—the researchers were able to analyze an exceptional dataset.

" This project demonstrates the power of participatory science. Well-trained volunteers, in the right network, can help generate exceptionally high-quality data at scales that would otherwise be impossible ," concludes Sébastien Puechmaille, study coordinator at the University of Montpellier.

Key words : Research, Science, Company