External Reinfection of a Fungal Pathogen Does not Contribute to Pathogen Growth

Abstract

Chytridiomycosis is an emerging infectious disease of amphibians caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), which has led to devastating declines in amphibian populations worldwide. Current theory predicts that Bd infections are maintained through both reproduction on the host’s skin and reinfection from sources outside of the host. To investigate the importance of external reinfection on pathogen burden, we infected captive-bred individuals of the highly susceptible Panamanian Golden Frog, Atelopus glyphus, and wild-caught glass frogs, Espadarana prosoblepon, with Bd. We housed the animals in one of three treatments: individually, in heterospecific pairs, and in conspecific pairs. For 8 weeks, we measured the Bd load and shedding rate of all frogs. We found that Atelopus had high rates of increase in both Bd load and shedding rate, but pathogen growth rates did not differ among treatments. The infection intensity of Espadarana co-housed with Atelopus was indistinguishable from those housed singly and those in conspecific pairs, despite being exposed to a large external source of Bd zoospores. Our results indicate that Bd load in both species is driven by pathogen replication within an individual, with reinfection from outside the host contributing little to the amplification of host fungal load.

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Acknowledgements

Daniel Medina, Edward Kabay and Molly Bletz helped with sample collection. Jorge Guerrel provided assistance and advice for animal care. Roberto Ibáñez was supported by the Panama Amphibian Rescue and Conservation project, and the Sistema Nacional de Investigación. Graziella V. DiRenzo was supported by a National Science Foundation Graduate Research Fellowship. This research was funded under NSF DEB 1120161 (PIs: KRL and KRZ) with ANAM permit #SE/AH-5-12.

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Contributions

GVD, KRL, TST conceived of and designed the study. TST and MSdV conducted the experiment. GVD executed data analysis, modeling, and co-wrote the first draft of the manuscript. TST conducted the experiments in RI’s laboratory, executed data analysis, modeling, and co-wrote the first draft of the manuscript. KRL was involved with experimental design, manuscript preparation and collected the original dataset. AVL performed the laboratory work in the KRZ laboratory. All authors edited the manuscript. The work was funded by KRL and KRZ.

Corresponding author

Correspondence to Tate S. Tunstall.

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The authors declare that they have no conflict of interest.

Data Availability

The datasets and R code used in the current study are available through GitHub: https://github.com/tatet2/AtelopusBdTranmission.

Statement of Animal Ethics

All applicable institutional and/or national guidelines for the care and use of animals were followed.

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DiRenzo, G.V., Tunstall, T.S., Ibáñez, R. et al. External Reinfection of a Fungal Pathogen Does not Contribute to Pathogen Growth. EcoHealth 15, 815–826 (2018). https://doi.org/10.1007/s10393-018-1358-x

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Keywords

  • Amphibians
  • Abiotic reservoir
  • Community
  • Disease
  • Epizootic
  • Chytridiomycosis
  • Panama
  • Multi-species
  • Tropical
  • Transmission