A new pathogenic fungus threatens bats

[Press release] - Published on May 28, 2025 in Press Room, 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 huge 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 overturns the current understanding of white-nose syndrome, revealing new information about the identity and diversity of the pathogens involved.

White Nose Syndrome, a disease we thought we knew well!

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

For almost 20 years, it was believed that the history of this pathogen was relatively simple: a single agent, an identified geographical origin (Europe), and well-established mechanisms. But new genetic data reveal a much more complex history, 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 to be the sole agent responsible for white nose syndrome. 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 these species has been introduced into North America. This discovery challenges the idea of a single pathogen and reveals the complexity of the disease's dynamics. It thus opens up new perspectives on the evolution of virulence and how these pathogens interact with their hosts depending on geographical contexts.

"We thought we knew our enemy, but we are now discovering that it is twofold, and potentially more complex than we imagined," summarizes Nicola Fischer, lead author of the study, who completed her PhD on the subject at 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 syndrome 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 that have not yet been affected by the first. Furthermore, even bat species that are beginning to recover from exposure to the first pathogen could face new challenges if the second spreads. This situation is reminiscent of the chytrid fungi that devastated amphibian populations, where the emergence of a second, more specialized species after an initial generalist species had devastating effects. In the case of the second species of P. destructans, it is still possible to take preventive action to strengthen global biosecurity and limit the risks associated with this new threat.

In Eurasia, both species of fungus are already present, but fungal populations are highly structured geographically. The main risk lies in the convergence of previously isolated populations, often caused by human activities. This could promote genetic recombination within the same species, a mechanism well known in fungi for generating new variants, some of which are more virulent. Such an emergence would pose a serious threat to Eurasian bats, even though they do not appear to have been affected so far.

The origin of its introduction to North America finally explained

Thanks to genetic analysis of more than 5,400 samples collected across Eurasia and North America, the study has for the first time accurately identified the region of origin of the strain responsible for the North American white-nose syndrome epidemic: the Podillia region of Ukraine. This area, home to some of the world's largest cave systems, has been a popular destination for international speleologists, particularly those from North America, since the end of the Soviet Union. The results suggest that the accidental introduction of the fungus into North America, likely through exchanges with cave explorers in New York State, where the disease was first detected, was the result of a single event. This work puts an end to nearly two decades of speculation about the origin of white-nose syndrome across the Atlantic and strikingly illustrates the impact that 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 in terms of the spread of pathogens, and underscores the urgent need for a better understanding of the "biological pollution" associated with human travel. Preventing the unintentional transport of pathogenic fungi such as Pseudogymnoascus destructans must become a priority in conservation and health management strategies, both for wildlife and for humans. Systematic and rigorous cleaning of caving equipment during trips is an essential measure: studies show that it drastically reduces the presence of viable spores and thus limits the spread of the fungus that causes white-nose syndrome.

Volunteers at the heart of scientific discovery

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

"This project demonstrates the power of participatory science. Well-trained volunteers, working within the right network, can help generate data of exceptional quality on a scale that would otherwise be impossible to achieve,"concludes Sébastien Puechmaille, study coordinator at the University of Montpellier.

Keywords: Research, Science, Company