White-Nose Syndrome: Human Activity in the Emergence of an Extirpating Mycosis

A set of principles and practical suggestions for equitable fieldwork in biology

Field biology is an area of research that involves working directly with living organisms in situ through a practice known as "fieldwork." Conducting fieldwork often requires complex logistical planning within multiregional or multinational teams, interacting with local communities at field sites, and collaborative research led by one or a few of the core team members. However, existing power imbalances stemming from geopolitical history, discrimination, and professional position, among other factors, perpetuate inequities when conducting these research endeavors. After reflecting on our own research programs, we propose four general principles to guide equitable, inclusive, ethical, and safe practices in field biology: be collaborative, be respectful, be legal, and be safe. Although many biologists already structure their field programs around these principles or similar values, executing equitable research practices can prove challenging and requires careful consideration, especially by those in positions with relatively greater privilege. Based on experiences and input from a diverse group of global collaborators, we provide suggestions for action-oriented approaches to make field biology more equitable, with particular attention to how those with greater privilege can contribute. While we acknowledge that not all suggestions will be applicable to every institution or program, we hope that they will generate discussions and provide a baseline for training in proactive, equitable fieldwork practices.

Landscape Genetic Connectivity and Evidence for Recombination in the North American Population of the White-Nose Syndrome Pathogen, Pseudogymnoascus destructans

White-Nose Syndrome is an ongoing fungal epizootic caused by epidermal infections of the fungus, Pseudogymnoascus destructans (P. destructans), affecting hibernating bat species in North America. Emerging early in 2006 in New York State, infections of P. destructans have spread to 38 US States and seven Canadian Provinces. Since then, clonal isolates of P. destructans have accumulated genotypic and phenotypic variations in North America. Using microsatellite and single nucleotide polymorphism markers, we investigated the population structure and genetic relationships among P. destructans isolates from diverse regions in North America to understand its pattern of spread, and to test hypotheses about factors that contribute to transmission. We found limited support for genetic isolation of P. destructans populations by geographic distance, and instead identified evidence for gene flow among geographic regions. Interestingly, allelic association tests revealed evidence for recombination in the North American P. destructans population. Our landscape genetic analyses revealed that the population structure of P. destructans in North America was significantly influenced by anthropogenic impacts on the landscape. Our results have important implications for understanding the mechanism(s) of P. destructans spread.

Phenotypic Divergence along Geographic Gradients Reveals Potential for Rapid Adaptation of the White-Nose Syndrome Pathogen, Pseudogymnoascus destructans, in North America

White-nose syndrome (WNS) is an ongoing epizootic affecting multiple species of North American bats, caused by epidermal infections of the psychrophilic filamentous fungus Pseudogymnoascus destructans Since its introduction from Europe, WNS has spread rapidly across eastern North America and resulted in high mortality rates in bats. At present, the mechanisms behind its spread and the extent of its adaptation to different geographic and ecological niches remain unknown. The objective of this study was to examine the geographic patterns of phenotypic variation and the potential evidence for adaptation among strains representing broad geographic locations in eastern North America. The morphological features of these strains were evaluated on artificial medium, and the viability of asexual arthroconidia of representative strains was investigated after storage at high (23°C), moderate (14°C), and low (4°C) temperatures at different lengths of time. Our analyses identified evidence for a geographic pattern of colony morphology changes among the clonal descendants of the fungus, with trait values correlated with increased distance from the epicenter of WNS. Our genomic comparisons of three representative isolates revealed novel genetic polymorphisms and suggested potential candidate mutations that might be related to some of the phenotypic changes. These results show that even though this pathogen arrived in North America only recently and reproduces asexually, there has been substantial evolution and phenotypic diversification during its rapid clonal expansion.IMPORTANCE The causal agent of white-nose syndrome in bats is Pseudogymnoascus destructans, a filamentous fungus recently introduced from its native range in Europe. Infections caused by P. destructans have progressed across the eastern parts of Canada and the United States over the last 10 years. It is not clear how the disease is spread, as the pathogen is unable to grow above 23°C and ambient temperature can act as a barrier when hosts disperse. Here, we explore the patterns of phenotypic diversity and the germination of the fungal asexual spores, arthroconidia, from strains across a sizeable area of the epizootic range. Our analyses revealed evidence of adaptation along geographic gradients during its expansion. The results have implications for understanding the diversification of P. destructans and the limits of WNS spread in North America. Given the rapidly expanding distribution of WNS, a detailed understanding of the genetic bases for phenotypic variations in growth, reproduction, and dispersal of P. destructans is urgently needed to help control this disease.

Combating the Triple Threat: The Need for a One Health Approach

We live in a world that is rapidly changing, complex, and progressively interconnected. The convergence of people, animals, and their products embedded in an ever-changing environment has created a new dynamic. This dynamic is characterized by new threats to the health of humans, animals, and the environment. In addition, the health of each of these three domains is profoundly and inextricably linked and elaborately connected. Our interconnectedness strongly suggests that our future success in improving health will be based on a new integrative, holistic, and collaborative approach termed One Health. One Health demands that we work across professions, disciplines, and old boundaries. The challenges to our health are unique and profound, and old solutions to our new "wicked" problems are no longer as relevant or effective as in the past. The concept of One Health is not new but has reemerged as a concept to both better understand the triple threats to health and to better address these contemporary challenges using new approaches. This article discusses the health threats to each domain and calls for a new model to confront these challenges by shifting strategies and interventions upstream, closer to the origins of the threats. One Health is a new paradigm that can be used to improve the health of people, animals, and our environment as a collective rather than restricting our actions to any single domain.

Modeling the environmental growth of Pseudogymnoascus destructans and its impact on the white-nose syndrome epidemic

White-nose syndrome (WNS) has had a devastating effect on North American bat populations. The causal agent of WNS is the fungal pathogen, Pseudogymnoascus destructans (Pd), which has been shown to persist in caves after the eradication of host populations. As nonpathogenic Pseudogymnoascus spp. display saprophytic growth and are among the most commonly isolated fungi from caves, we examined whether Pd could grow in cave sediments and the contribution such growth could have to WNS disease progression. We inoculated a range of diverse cave sediments and demonstrated the growth of Pd in all sediments tested. These data indicate that environmental growth of Pd could lead to the accumulation of spores above the estimated infection threshold for WNS, allowing environment-to-bat infection. The obtained growth parameters were then used in a susceptible-infected-susceptible mathematic model to determine the possible contribution of environmental Pd growth to WNS disease progression in a colony of little brown bats (Myotis lucifugus). This model suggests that the environmental growth of Pd would increase WNS infection rates, particularly in colonies experiencing longer hibernation periods or in hibernacula with high levels of organic detritus. The model also suggests that once introduced, environmental Pd growth would allow the persistence of this pathogen within infected hibernacula for decades, greatly compromising the success of bat reintroduction strategies. Together these data suggest that Pd is not reliant on its host for survival and is capable of environmental growth and amplification that could contribute to the rapid progression and long-term persistence of WNS in the hibernacula of threatened North American bats.

Comparison of the white-nose syndrome agent Pseudogymnoascus destructans to cave-dwelling relatives suggests reduced saprotrophic enzyme activity

White-nose Syndrome (WNS) is an emerging infectious mycosis that has impacted multiple species of North American bats since its initial discovery in 2006, yet the physiology of the causal agent, the psychrophilic fungus Pseudogymnoascus destructans ( = Geomyces destructans), is not well understood. We investigated the ability of P. destructans to secrete enzymes that could permit environmental growth or affect pathogenesis and compared enzyme activity across several Pseudogymnoascus species isolated from both hibernating bats and cave sediments. We found that P. destructans produced enzymes that could be beneficial in either a pathogenic or saprotrophic context, such as lipases, hemolysins, and urease, as well as chitinase and cellulases, which could aid in saprotrophic growth. The WNS pathogen showed significantly lower activity for urease and endoglucanase compared to con-generic species (Pseudogymnoascus), which may indicate a shift in selective pressure to the detriment of P. destructans’ saprotrophic ability. Based on the positive function of multiple saprotrophic enzymes, the causal agent of White-nose Syndrome shows potential for environmental growth on a variety of substrates found in caves, albeit at a reduced level compared to environmental strains. Our data suggest that if P. destructans emerged as an opportunistic infection from an environmental source, co-evolution with its host may have led to a reduced capacity for saprotrophic growth.