Emerging infectious diseases (EIDs) affect numerous human and wildlife populations. EID emergence is frequently associated with ecologically disruptive human activities such as urbanization, the trade in wildlife, pollution, and land-use change. The movement of wild animals for consumption, research, bait, or the pet trade can increase the risk of EID spread. The global trade in amphibians is thought to contribute to the widespread EID, chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd). Bd exists in several genetically distinct lineages worldwide. Nonnative amphibians and the nonnative pathogens they carry pose a hazard to endemic amphibian species upon intentional or accidental release. Comparative experiments exploring the range of infection dynamics among different host species and Bd strains can reveal the possible consequence of amphibian trading or release.
To explore virulence variation among different Bd strains across multiple amphibian host species, we examined infection outcomes, survival and infection load, in three co-occurring host species (Pacific treefrog, Western toad, and Cascades frog) after exposure to three different New World Bd strains [isolated in Oregon (USA), California (USA), and El Cope (Panama); an additional fourth strain from Maine (USA) was tested in toads].
Our results show that infection outcomes depend on the interaction between host and Bd strain type. Western toads experienced lower survival compared to Cascades frog and Pacific treefrogs, supporting previous research positing this species’ sensitive status. However, toad survival was not uniform among all Bd strains, only exposure to two Bd strains (Panama and California) resulted in significantly lowered survival. We also documented strain dependent differences in Bd infection load for toads. Exposure to the Bd strain from Panama yielded the highest pathogen loads compared to all other strains, and while toads exposed to California Bd experienced increased mortality, their pathogen loads were equal to the other Bd strain treatments.
Our study reveals virulence variation among amphibian species and Bd strain type, outcomes that might be obscured if only testing a single host species or pathogen strain.