Search

Pathogenic fungi have substantial effects on global biodiversity, and 2 emerging pathogenic species—the chytridiomycete Batrachochytrium dendrobatidis, which causes chytridiomycosis in amphibians, and the ascomycete Geomyces destructans, which causes white-nose syndrome in hibernating bats—are implicated in the widespread decline of their vertebrate hosts. We synthesized current knowledge for chytridiomycosis and white-nose syndrome regarding disease emergence, environmental reservoirs, life history characteristics of the host, and host–pathogen interactions. We found striking similarities between these aspects of chytridiomycosis and white-nose syndrome, and the research that we review and propose should help guide management of future emerging fungal diseases.

Unlike bats in North America, bats in Europe are not killed by this fungus., White-nose syndrome is an emerging disease in North America that has caused substantial declines in hibernating bats. A recently identified fungus (Geomyces destructans) causes skin lesions that are characteristic of this disease. Typical signs of this infection were not observed in bats in North America before white-nose syndrome was detected. However, unconfirmed reports from Europe indicated white fungal growth on hibernating bats without associated deaths. To investigate these differences, hibernating bats were sampled in Germany, Switzerland, and Hungary to determine whether G. destructans is present in Europe. Microscopic observations, fungal culture, and genetic analyses of 43 samples from 23 bats indicated that 21 bats of 5 species in 3 countries were colonized by G. destructans. We hypothesize that G. destructans is present throughout Europe and that bats in Europe may be more immunologically or behaviorally resistant to G. destructans than their congeners in North America because they potentially coevolved with the fungus.

White-nose syndrome is caused by the fungus Geomyces destructans and is responsible for the deaths of >1,000,000 bats since 2006. This disease and fungus had been restricted to the northeastern United States. We detected this fungus in a bat in France and assessed the implications of this finding.

To the Editor: Emerging infectious diseases have caused catastrophic declines in wildlife populations, and the introductions of many pathogen have been linked to increases in global trade and travel (1). Mapping the distribution of pathogens is necessary to identify species and populations at risk and identify sources of pathogen spillover and introduction. Once pathogen distributions are known, management actions can be taken to reduce the risk for future global spread (2). Bats with symptoms of white-nose syndrome (WNS) were first detected in the United States in 2006, and the disease has subsequently caused precipitous declines in temperate bat populations across eastern North America (3,4). Pseudogymnoascus destructans, the causative agent of WNS, is a cold-growing fungus that infects bats’ skin during hibernation, leading to more frequent arousals from torpor and death (3). P. destructans is widespread throughout Europe (5), but, to our knowledge, its presence in Asia has not been documented. We sampled bats and hibernacula surfaces (cave walls and ceilings) across northeastern China during 2 visits (June–July 2014 and March 2015) using a previously described swab-sampling technique (6). Bats were captured inside caves and at their entrances. DNA was extracted from samples by using a modified QIAGEN DNeasy blood and tissue kit (QIAGEN, Valencia, CA, USA) and tested in duplicate for the presence of P. destructans with a quantitative real-time PCR (qPCR) (6,7). In the summer of 2014 and winter of 2015, we collected 385 samples from hibernacula surfaces at 12 sites in 3 provinces and 1 municipality (Figure, panel A) and 215 samples from 9 species of bats at 10 sites (summer: Rhinolophus ferrumequinum, Rhinolophus pusillus, Myotis adversus, Myotis macrodactylus, Myotis pilosus, Myotis chinensis, Murina usseriensis; winter: R. ferrumequinum, Murina leucogaster, Myotis petax). During the summer, P. destructans was widely distributed across the study region with positive samples (determined on the basis of qPCR results) obtained from cave surfaces at 9 of 12 sites and from bats at 2 of the 9 sites where bats were sampled (Figure, panel A). Figure A) Distribution of Pseudogymnoascus destructans in cave environments during summer at 9 sites in northeastern China. Pie charts show the prevalence (red indicates fraction of positive samples) of P. destructans, and the size of pie graphs indicates the ... Prevalence of P. destructans was low during summer in the environment (mean prevalence across sites 0.06 ± 0.03) and in bats. Bats of 3 species tested positive for P. destructans in the summer: M. macrodactylus (1/10), M. chinensis (1/1), and M. ussuriensis (1/1). P. destructans was not detected in bats of 4 other species, of which >20 individual animals of each species were sampled (R. ferrumequinum, R. pusillus, M. pilosus, and M. adversus). The low prevalence of P. destructans in bats and on hibernacula surfaces in China during the summer was similar to comparable results from studies in North America (6). In winter, prevalence at the 2 sites we revisited was much higher; 75% of 85 samples from 3 species tested positive, including samples from 16/17 M. petax bats. We also detected P. destructans in bats from 2 additional species (R. ferrumequinum [11/19 bats] and M. leucogaster [11/16 bats]). In addition, during March 2015, we observed visual evidence of P. destructans in bats (M. petax; Figure, panel C) and obtained 2 fungal cultures from swab specimens taken from these bats. To isolate P. destructans from these samples, we plated swab specimens from visibly infected bats on Sabouraud dextrose agar at 10°C. We identified potential P. destructans isolates on the basis of morphologic characteristics. DNA was then extracted from 2 suspected fungal cultures and tested for P. destructans by qPCR, as previously described. To further confirm the presence of P. destructans, we prepared the fungal isolates for Sanger sequencing (Technical Appendix). The 600-nt amplification products from these 2 isolates were sequenced and found to be 100% identical to the P. destructans rRNA gene region targeted for amplification. In addition, using BLAST (http://www.ncbi.nlm.nih.gov/blast.cgi), we found that sequences were a 100% match with isolates from Europe (GenBank accession no. {"type":"entrez-nucleotide","attrs":{"text":"GQ489024","term_id":"284944064","term_text":"GQ489024"}}GQ489024) and North America (GenBank accession no. {"type":"entrez-nucleotide","attrs":{"text":"EU884924","term_id":"211905147","term_text":"EU884924"}}EU884924). This result confirms that the same species of fungus occurs on all 3 continents. We also obtained wing biopsy punches from these bats and found lesions characteristic of WNS by histopathologic examination (Figure, panel B; Technical Appendix). The occurrence of P. destructans at most sites sampled indicates that this pathogen is widespread in eastern Asia (Figure, panel A). The presence of P. destructans in bats from 6 species in China and on bats in 13 species in Europe (8) confirms the generalist nature of this fungus and suggests that it may occur throughout Eurasia (Figure, panel D). Decontamination and restrictions on the use of equipment that has been used in caves in Asia would help reduce the probability of introducing P. destructans to uninfected bat populations (e.g., western North America, New Zealand, southern Australia, and temperate areas of South America). These measures would also reduce the risk of introducing new strains of P. destructans to regions where bats are already infected (e.g., eastern North America and Europe). These measures are necessary to prevent the devastating effects this pathogen has had on bats in North America and would help maintain the ecosystem services that bats provide (9,10). Technical Appendix: The Technical Appendix describes the DNA sequencing of fungal isolates to confirm the presence of Pseudogymnoascus destructans and histologic examination of bat fungal lesions. Click here to view.(238K, pdf)

To the Editor: Bat geomycosis (white nose syndrome) is caused by the psychrophilic fungus Geomyces destructans, which has rapidly spread in the United States and Canada since it was first reported from Albany, New York (1,2). In 2011, a single genotype of G. destructans was found in bats with geomycosis in different parts of New York (3). The findings raised the possibility of clonal spread of a new pathogen with serious implications for the survival of the affected bat populations (4). To provide information for devising conservation measures, we explored whether this emerging infectious disease is caused by a novel pathogen (5). To do so, we genotyped G. destructans isolates from the midwestern and southern United States. During 2010 and 2011, a total of 11 cultures of G. destructans were isolated and identified: 1 each from Pennsylvania and Ohio, 3 from North Carolina, and 6 from West Virginia (Figure). The cultures came from 8 little brown bats (Myotis lucifugus) and 3 tri-colored bats (Perimyotis subflavus). Two recent G. destructans isolates from New York and 1 G. pannorum isolate were included as controls. Genomic DNA was prepared from fungal growth by the conventional glass bead treatment, phenol–chloroform extraction, and ethanol precipitation. PCR amplifications of 8 G. destructans gene fragments (ALR, Bpntase, DHC1, GPHN, PCS, POB3, SRP72, and VPS13) were performed as described (3). The amplicons were sequenced and nucleotides were aligned by Sequencher 4.8 (www.genecodes.com); phylogenetic analyses were done using PAUP*4.0 software (www.sinauer.com). Figure A) Consensus maximum-parsimony tree of 8 concatenated gene fragments of Geomyces destructans. Data were derived from 13 G. destructans test isolates. G. destructans M1379 and G. pannorum M1378 were used as controls in this study; they were described in ... A total of 4,722 nt sequences were obtained from 8 gene fragments of 13 G. destructans isolates (GenBank accession nos. {"type":"entrez-nucleotide-range","attrs":{"text":"JQ029780-JQ029883","start_term":"JQ029780","end_term":"JQ029883","start_term_id":"380040511","end_term_id":"380040717"}}JQ029780-JQ029883) and 1 G. pannorum isolate (GenBank accession nos. {"type":"entrez-nucleotide","attrs":{"text":"HQ834330","term_id":"386776025","term_text":"HQ834330"}}HQ834330, {"type":"entrez-nucleotide","attrs":{"text":"HQ834347","term_id":"386776059","term_text":"HQ834347"}}HQ834347, {"type":"entrez-nucleotide","attrs":{"text":"HQ834364","term_id":"386776093","term_text":"HQ834364"}}HQ834364, {"type":"entrez-nucleotide","attrs":{"text":"HQ834381","term_id":"386776127","term_text":"HQ834381"}}HQ834381, {"type":"entrez-nucleotide","attrs":{"text":"HQ834398","term_id":"386776161","term_text":"HQ834398"}}HQ834398, {"type":"entrez-nucleotide","attrs":{"text":"HQ834415","term_id":"386776195","term_text":"HQ834415"}}HQ834415, {"type":"entrez-nucleotide","attrs":{"text":"HQ834432","term_id":"386776229","term_text":"HQ834432"}}HQ834432, and {"type":"entrez-nucleotide","attrs":{"text":"HQ834449","term_id":"386776263","term_text":"HQ834449"}}HQ834449). Multiple alignments of these sequences showed 100% identity, and the aligned nucleotides matched perfectly with those of earlier G. destructans sequences for the same gene fragments analyzed from New York isolates (3). The nucleotide alignments of 8 sequences showed differences from those obtained from the closely related fungus, G. pannorum. Maximum-parsimony trees were generated by using sequences from each gene fragment. These trees showed a single clade of G. destructans strains distinct from G. pannorum; similar topologies were obtained when different phylogenetics methods were used for analysis (details not shown). A consensus maximum-parsimony tree derived from the 8 concatenated gene fragments also showed a single clade of G. destructans isolates from New York and the midwestern and southern United States (Figure). The data obtained in this study strongly indicate further clonal spread of G. destructans from its origin near Albany, New York. The locations in which G. destructans was detected in the current study were spread across 5 states, which were >800 miles from Albany. The test isolates were compared with a New York isolate from 2008, which provided a 4-year temporal variation in our sampling. Bats of 2 species were positive for G. desctructans in the current samples, and they yielded the same G. destructans genotype. Thus, there is evidence for host-independent spread of a single clone of G. destructans. These data would support the novel-pathogen hypothesis for the origin of bat geomycosis (5). However, these conclusions are based on limited sampling because isolations of G. destructans from affected bats are uncommon. The demonstration of pure fungal culture in the affected animals is still not the standard for geomycosis diagnostics, and most geomycosis is confirmed by bat morphologic appearance or histopathologic examination. Additionally, our phylogenetics analyses were limited to ≈5 kbp of fungal genomes, which could lead to sampling bias (3). Ideally, a large number of G. destructans isolates, including isolates from Europe, and additional polymorphic markers would be needed to determine the novel or local origin of this pathogen (6,7). The environmental factors that led to introduction or reemergence of G. destructans in mines and caves remain unknown, and their contribution in the spread of the fungus through air, water, and soil is yet to be determined (8). Although no direct evidence has emerged, a role for anthropomorphic activities (occupational or recreational) in this spread is a distinct possibility (9). We provide genetic evidence for further spread of a single genotype of G. destructans from Albany, New York, to locations in the midwestern and southern United States. Experimental transmission of geomycosis from infected bats to healthy bats by direct contact has recently been confirmed (10). Therefore, G. destructans might be rapidly spreading along summer and winter migration routes of bats, which present ample opportunities for mixing of healthy and diseased animals.