Abstract
Recent outbreaks of chytridiomycosis, the disease of amphibians caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), have contributed to population declines of numerous amphibian species worldwide. The devastating impacts of this disease have led researchers to attempt drastic conservation measures to prevent further extinctions and loss of biodiversity. The conservation measures can be labour-intensive or expensive, and in many cases have been unsuccessful. We developed a mathematical model of Bd outbreaks that includes the effects of demographic stochasticity and within-host fungal load dynamics. We investigated the impacts of one-time treatment conservation strategies during the disease outbreak that occurs following the initial arrival of Bd into a previously uninfected frog population. We found that for all versions of the model, for a large fraction of parameter space, none of the one-time treatment strategies are effective at preventing disease-induced extinction of the amphibian population. Of the strategies considered, treating frogs with antifungal agents to reduce their fungal load had the greatest likelihood of a beneficial outcome and the lowest risk of decreasing the persistence of the frog population, suggesting that this disease mitigation strategy should be prioritized over disinfecting the environment or reducing host density.
Highlights
Amphibian populations around the world are being severely impacted by the disease chytridiomycosis, caused by the chytrid fungus Batrachochytrium dendrobatidis [1,2]
It is unlikely that every individual in an amphibian population can be captured and treated, or that Batrachochytrium dendrobatidis (Bd) zoospores can be completely eliminated from the habitat
Of the treatment options considered, we found that using any of the available antifungal protocols to clear the infection from at least a fraction of the frogs is the most likely to have a beneficial outcome, and is relatively unlikely to reduce amphibian population persistence
Summary
Amphibian populations around the world are being severely impacted by the disease chytridiomycosis, caused by the chytrid fungus Batrachochytrium dendrobatidis (commonly referred to as ‘Bd’) [1,2]. The amphibian chytrid fungus Bd is transmitted via a motile, aquatic zoospore. The zoospore encysts on keratinized tissues of amphibian hosts (which occur in the mouthparts of tadpoles, and in the skin of post-metamorphic stages), and develops a single sporangium ( called zoosporangium, the structure in which spores are formed). New zoospores (motile spore that uses a flagellum for locomotion) develop in the sporangium and are released to the environment [23,24], Bd can sometimes spread from cell to cell within amphibian skin [25]. The outcome of infection with Bd, varies greatly between amphibian species, with adults of some species succumbing rapidly to chytridiomycosis and others showing high levels of tolerance to infection with the fungus [1,2]. In a number of species, infected individuals are not impacted by low-level infections (with low fungal loads) but die when fungal loads are high [37]
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