White-nose disease (WND), caused by the psychrophilic fungus Pseudogymnoascus destructans, represents one of the greatest threats for North American hibernating bats. Research on molecular data has significantly advanced our knowledge of various aspects of the disease, yet more studies are needed regarding patterns of P. destructans genetic diversity distribution. In the present study, we investigate three sites within the native range of the fungus in detail: two natural hibernacula (karst caves) in Bulgaria, south-eastern Europe and one artificial hibernaculum (disused cellar) in Germany, northern Europe, where we conducted intensive surveys between 2014 and 2019. Using 18 microsatellite and two mating type markers, we describe how P. destructans genetic diversity is distributed between and within sites, the latter including differentiation across years and seasons of sampling; across sampling locations within the site; and between bats and hibernaculum walls. We found significant genetic differentiation between hibernacula, but we could not detect any significant differentiation within hibernacula, based on the variables examined. This indicates that most of the pathogen’s movement occurs within sites. Genotypic richness of P. destructans varied between sites within the same order of magnitude, being approximately two times higher in the natural caves (Bulgaria) compared to the disused cellar (Germany). Within all sites, the pathogen’s genotypic richness was higher in samples collected from hibernaculum walls than in samples collected from bats, which corresponds with the hypothesis that hibernacula walls represent the environmental reservoir of the fungus. Multiple pathogen genotypes were commonly isolated from a single bat (i.e. from the same swab sample) in all study sites, which might be important to consider when studying disease progression.

The bat immune system features multiple unique properties such as dampened inflammatory responses and increased tissue protection, explaining their long lifespan and tolerance to viral infections. Here, we demonstrated that body temperature fluctuations corresponding to different physiological states in bats exert a large impact on their antibody repertoires. At elevated temperatures typical for flight, IgG from the bat species Myotis myotis and Nyctalus noctula show elevated antigen binding strength and diversity, recognizing both pathogen-derived antigens and autoantigens. The opposite is observed at temperatures reflecting inactive physiological states. IgG antibodies of human and other mammals, or antibodies of birds do not appear to behave in a similar way. Importantly, diversification of bat antibody specificities results in preferential recognition of damaged endothelial and epithelial cells, indicating an anti-inflammatory function. The temperature-sensitivity of bat antibodies is mediated by the variable regions of immunoglobulin molecules. Additionally, we uncover specific molecular features of bat IgG, such as low thermodynamic stability and implication of hydrophobic interactions in antigen binding as well as high prevalence of polyreactivity. Overall, our results extend the understanding of bat tolerance to disease and inflammation and highlight the link between metabolism and immunity.

The emergence of infectious diseases, particularly those caused by fungal pathogens, poses serious threats to public health, wildlife and ecosystem stability¹. Host–fungus interactions and environmental factors have been extensively examined^2–4. However, the role of genetic variability in pathogens is often less well-studied, even for diseases such as white-nose in bats, which has caused one of the highest disease-driven death tolls documented in nonhuman mammals⁵. Previous research on white-nose disease has primarily focused on variations in disease outcomes attributed to host traits or environmental conditions^6–8, but has neglected pathogen variability. Here we leverage an extensive reference collection of 5,479 fungal isolates from 27 countries to reveal that the widespread causative agent is not a single species but two sympatric cryptic species, each exhibiting host specialization. Our findings provide evidence of recombination in each species, but significant genetic differentiation across their genomes, including differences in genome organization. Both species contain geographically differentiated populations, which enabled us to identify the species introduced to North America and trace its source population to a region in Ukraine. In light of our discovery of the existence of two cryptic species of the causative agent of white-nose disease, our research underscores the need to integrate the study of pathogen variability into comprehensive disease surveillance, management and prevention strategies. This holistic approach is crucial for enhancing our understanding of diseases and implementing effective measures to prevent their spread.

Healthy wing membranes are essential for bats. They are critical for maintaining the water balance and, during hibernation, they protect the bat’s body from dehydration. Assessing the state of the membrane visually is an easy and effective way to monitor a bat’s health and discover abnormal structures and infections in wild bat populations. During pre- and post-hibernation surveys of bats’ wings, we identified the presence of skin mites, Psorergatoides kerivoulae (Fain, 1959). The parasite causes cutaneous lesions on the wing membranes of the greater moused-eared bat, Myotis myotis (Borkhausen, 1797) and the lesser moused-eared bat, Myotis blythii (Tomes, 1857). The lesser mouse-eared bat is a new host for this parasite. Our study is the first to describe the histopathology of the infection on the wings of the greater and lesser mouse-eared bats. To our knowledge, this is the southernmost record of this parasite and the first mention of the genus Psorergatoides for the Balkans.

Veryovkina Cave is the world’s deepest known cave (2212 m deep). It is located in the Arabika Massif of Gagra Mountain in the Western Caucasus. Its microbiome remains unknown because of difficulties in access. Ten sediment samples were collected at vertical depths ranging from 300 m to 2204 m; they varied by substrate type, moisture content, and visitor accessibility. Total microbial DNA was isolated, and 16S ribosomal gene metabarcoding was applied for taxonomic identification. Seven samples showed reliable content, whereas three samples indicated no recoverable reads. Proteobacteria, Acidobacteria, and Actinobacteria were the most abundant phyla in total. Depth stratification of microbiota showed that (1) shallow wet clays were dominated by Acidimicrobia and Actinobacteria; (2) mid-depth wet clays showed the highest abundance of Nitrospira, Betaproteobacteria, and Vicinamibacter; and (3) deep, dry substrates were dominated by Thermoleophilia and Rubrobacteria. Multivariate analyses showed that substrate type and moisture tended to explain more variation in microbial abundance than depth or human activity. We demonstrate the presence of distinct ecological niches within the cave ecosystem, which emphasizes the role of local conditions in shaping microbial diversity.

White-nose disease (WND) is a deadly disease in hibernating bats. Its causal agent is the fungus Pseudogymnoascus destructans (Pd) that was only recently introduced to North America, where it causes pervasive mortality. In contrast, it is native to Eurasia, where bats do not experience mass mortality. The pathogen successfully survives for long periods in cave substrates (e.g., mud, soil) as well as on contaminated caving clothes and equipment. This emphasizes the importance of limiting its human-mediated spread, particularly over long distances and from areas where it is native and genetically highly diverse. To assess associated conservation risks more precisely, we conducted a global online survey on cavers’ WND knowledge, travel frequencies, and hygiene habits regarding caving equipment, and we analysed the relationship between those variables. We interpreted our results based on respondents’ continents of origin, separating them into 3 categories: continents where Pd was recently introduced and continues to cause significant bat mortality (North America); continents where Pd is currently not present but is hypothesized to cause bat mortality if introduced (Australia and South and Central America); and continents where Pd is native and currently not associated with bat mortality (Europe and Asia). We found significant differences between categories, showing that further awareness of WND is most needed in Europe and Asia where specific guidelines for limiting Pd spread are still to be developed. Interestingly, however, WND knowledge alone explained very little variance in respondents’ hygiene habits, showing that other factors such as habits, emotions, or personal values have a stronger influence on cavers’ behaviour.