Amphibian chytrid fungus in a rain-forest frog assemblage 30 years after invasion: Does chytridiomycosis still kill frogs?

Chytridiomycosis, caused by infection with the chytrid fungus Batrachochytrium dendrobatidis (Bd), is an emerging infectious disease of amphibians implicated in global declines and extinctions. At least 207 species worldwide have been affected, and chytridiomycosis thus represents the most devastating disease of vertebrates in recorded history. Populations that have suffered declines have been repeatedly documented. However, little research has been carried out on populations that have survived or begun to recover and in which Bd continues to thrive. We are investigating the dynamics of Bd infections at the community level in frog populations along rainforest streams in south-east Queensland, Australia, where two frog species were lost to extinction at around the time of Bd invasion. Despite the presence of Bd infections for at least 29 years in this area, several endangered species have persisted and begun to recover post-decline. Initial results from disease surveys and capture-mark-recapture (CMR) modelling analyses suggest that while Bd is still associated with some mortalities, many frogs in the field survive infections for long periods and the effect of Bd on individual survival is not obvious. Low mortality of infected individuals coupled with high disease prevalence (up to 70%) within sampled populations support the hypothesis that a shift in the host-pathogen relationship that favours frog survival may have occurred. This finding has significant implications for species conservation, and offers hope for the recovery of impacted amphibian species worldwide.