Understanding the pieces of the amphibian disease puzzle

Rick Speare

School of Public Health and Tropical Medicine, James Cook University, Townsville, Queensland, Australia 4811.
Email: richard.speare@jcu.edu.au

Powerpoint presentation of talk (740kb)

Communicable disease concepts will be briefly discussed; inoculating dose, primary pathogenicity, infection triad of host, pathogen and environment, concept that death is an insensitive indicator of infection, and emerging infectious diseases. The infectious agent causing the catastrophic declines of wild amphibians has a specific profile: high virulence, low host specificity, sparing tadpoles, association with water, and after frogs have disappeared persistence as an endemic pathogen in either another host or in the environment.

Few amphibian pathogens cause epidemic disease (Batrachochytrium dendrobatidis, ranaviruses, and some bacteria from the Vibroniaceae) and only one, B. dendrobatidis, meets the profile given above. Various aspects of chytridiomycosis will be discussed including the data proving primary pathogenicity, current distribution of B. dendrobatidis, and the current status of evidence for the role of B. dendrobatidis in amphibian declines. The various strategies available to lessen the risks of infectious agents to wild amphibians will be outlined including elimination of pathogens, preventing introduction of infected animals into pathogen-free areas, decreasing the number of infectious units of specific pathogens (lowering the inoculating dose) including limiting movement between contaminated areas and protocols on handling wild amphibians, disease modification by decreasing the impact of infection on the host including the importance of optimal environments, and technological strategies such as husbandry, gene and somatic cell preservation and cloning. The list of options available highlight that the impact of infectious agents even in wild populations are controllable, and that feasible strategies can be implemented particularly with government support.