Parallels in Amphibian and Bat Declines from Pathogenic Fungi

Evan A. Eskew¹ and Brian D. Todd¹

Author affiliations: Author affiliation: University of California, Davis, California, USA

Abstract

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.

Fungi and fungus-like organisms have been recognized historically as prominent plant pathogens that can have detrimental effects on agricultural crops and wild flora (1,2). Fisher et al. (3) recently reviewed the increasing role and recognition of pathogenic fungi that affect global biodiversity. Their analyses showed that most (91%) recent extinctions and extirpations caused by fungal disease have affected animals rather than plants. In particular, 2 emerging pathogenic fungi—the chytridiomycete Batrachochytrium dendrobatidis, which causes chytridiomycosis in amphibians (4,5), and the ascomycete Geomyces destructans, which causes white-nose syndrome (WNS) in hibernating bats (6)—are implicated in the widespread decline of their vertebrate hosts. In general, increased global biosecurity and monitoring are recommended to prevent and manage emerging fungal diseases (3), but there are also pressing research needs that can help specifically address these 2 devastating pathogenic fungi. We call attention to parallels between chytridiomycosis and WNS and highlight areas where urgent research is required (Table). Comparison of these diseases also illustrates broader themes and questions that can be used to direct research on future emerging fungal diseases.

Disease Emergence

Effective control of any disease requires understanding of the processes that have resulted in its emergence. The study of a pathogen’s geographic origin and phylogenetic history often provides critical insight in this regard. In general, infectious diseases can emerge from 2 distinct scenarios: 1) the geographic spread of a novel pathogen into a new area with naive hosts or 2) a shift in pathogenicity or host specificity of an endemic pathogen as a result of environmental changes that alter host–pathogen interactions (25). Current evidence predominantly suggests that chytridiomycosis and WNS outbreaks are driven by anthropogenic transport of novel pathogenic fungi into new geographic regions.