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Open Access Highly Accessed Research article

Tolerance of fungal infection in European water frogs exposed to Batrachochytrium dendrobatidis after experimental reduction of innate immune defenses

Douglas C Woodhams14*, Laurent Bigler2 and Rachel Marschang3

Author Affiliations

1 Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, Zurich, CH-8057, Switzerland

2 Institute of Organic Chemistry, University of Zurich, Winterthurerstrasse 190, Zurich, CH-8057, Switzerland

3 Institute for Environmental and Animal Hygiene, University of Hohenheim, Garbenstrasse 30, Stuttgart, 70599, Germany

4 Department of Ecology and Evolutionary Biology, University of Colorado, N122 Ramaley, 334 UCB, Boulder, CO, 80309-0334, USA

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BMC Veterinary Research 2012, 8:197  doi:10.1186/1746-6148-8-197

Published: 23 October 2012

Abstract

Background

While emerging diseases are affecting many populations of amphibians, some populations are resistant. Determining the relative contributions of factors influencing disease resistance is critical for effective conservation management. Innate immune defenses in amphibian skin are vital host factors against a number of emerging pathogens such as ranaviruses and the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). Adult water frogs from Switzerland (Pelophylax esculentus and P. lessonae) collected in the field with their natural microbiota intact were exposed to Bd after experimental reduction of microbiota, skin peptides, both, or neither to determine the relative contributions of these defenses.

Results

Naturally-acquired Bd infections were detected in 10/51 P. lessonae and 4/19 P. esculentus, but no disease outbreaks or population declines have been detected at this site. Thus, this population was immunologically primed, and disease resistant. No mortality occurred during the 64 day experiment. Forty percent of initially uninfected frogs became sub-clinically infected upon experimental exposure to Bd. Reduction of both skin peptide and microbiota immune defenses caused frogs to gain less mass when exposed to Bd than frogs in other treatments. Microbiota-reduced frogs increased peptide production upon Bd infection. Ranavirus was undetectable in all but two frogs that appeared healthy in the field, but died within a week under laboratory conditions. Virus was detectable in both toe-clips and internal organs.

Conclusion

Intact skin microbiota reduced immune activation and can minimize subclinical costs of infection. Tolerance of Bd or ranavirus infection may differ with ecological conditions.

Keywords:
Amphibian; Antimicrobial peptide; Chytridiomycosis; MALDI-MS; Microbiota; Pelophylax; Ranavirus