New study reveals that not one, but two pathogenic species cause white-nose disease in hibernating bats

An international team of researchers led by the University of Montpellier, with the participation of Dr Violeta Zhelyazkova from the National Museum of Natural History, Sofia at the Bulgarian Academy of Sciences (NMNHS), has completed the largest population-genetic analysis to date of the pathogenic fungus Pseudogymnoascus destructans. This fungus is the causative agent of white-nose disease (WND) in hibernating bats and stays behind one of the most massive die-offs of wild mammals in modern history. The study, based on 5,479 genotyped fungal samples and nearly 20 deeply sequenced full genomes, reveals a second cryptic species of white-nose fungus and is published in the prestigious journal Nature. The paper, led by Dr Nicola Fischer, is freely available on the Nature website.

WND was first observed during the winter of 2006—2007 in a cave in New York State and owes its name to the white fungal growth on the muzzles, wings, and ears of bats. Its causative agent, the psychrophilic dermatophytic fungus Pseudogymnoascus destructans, is a species new to science that affects only bats in hibernation, yet survives in cave substrates. The epidemic has spread across almost all of North America, claiming millions of victims and causing severe damage to ecosystems. In 2011, the pathogen was first detected outside the continent by Dr Sebastian Puechmaille, the lead of the present study, and in 2014, Violeta Zhelyazkova and Nia Toshkova, then interns at NMNHS, confirmed its presence in Bulgaria. These and other findings revealed that the fungus is widespread across Europe and Asia, but without causing mass mortality.

Earlier population-genetic studies on the topic revealed the Eurasian origin of P. destructans and its recent introduction to North America—a textbook case of pathogen pollution. However, only the present study, thanks to the unprecedented number of samples provided by the authors and 360 volunteers, achieves sufficient resolution to uncover the existence of a second species of white-nose fungus in Eurasia. The newly discovered pathogen, provisionally named Pd2, is sympatric with P. destructans sensu stricto (Pd1) but exhibits different host preferences: Pd1 primarily infects greater mouse-eared bats (Myotis myotis), whereas Pd2 affects Daubenton’s bats (Myotis daubentonii). The study results also provide extremely high-resolution data on the fungal population structure, whose genotypes are rarely shared between separate subterranean habitats. This has allowed researchers to identify the likely point of Pd1’s introduction from Europe to North America: the Podilia region in Western Ukraine, home of the longest gypsum caves in the world.

Thanks to her excellent physical and technical training, Dr Zhelyazkova managed to collect samples from several deep Bulgarian caves. She subsequently carried out part of the laboratory work involving the cultivation and isolation of pure fungal cultures, genotyping, and population-genetic analysis of the Bulgarian samples, and participated in the interpretation of the results regarding the role of speleologists in P. destructans spread.

The discoveries fundamentally change our understanding of WND and provide fascinating insights into the evolution of virulence in fungal pathogens. The information obtained could help prevent the introduction of Pd2 into North America or other regions and thus prevent a second wave of this dangerous epidemic.