Pathogenesis of Chytridiomycosis, a Cause of Catastrophic Amphibian Declines

Abstract

The pathogen Batrachochytrium dendrobatidis (Bd), which causes the skin disease chytridiomycosis, is one of the few highly virulent fungi in vertebrates and has been implicated in worldwide amphibian declines. However, the mechanism by which Bd causes death has not been determined. We show that Bd infection is associated with pathophysiological changes that lead to mortality in green tree frogs (Litoria caerulea). In diseased individuals, electrolyte transport across the epidermis was inhibited by >50%, plasma sodium and potassium concentrations were respectively reduced by approximately 20% and approximately 50%, and asystolic cardiac arrest resulted in death. Because the skin is critical in maintaining amphibian homeostasis, disruption to cutaneous function may be the mechanism by which Bd produces morbidity and mortality across a wide range of phylogenetically distant amphibian taxa.

Disease and the dynamics of extinction

“…It appears to be capable of causing the extinction of Tasmanian devil populations because the rate of transmission depends weakly, if at all, on host population density [41]. The amphibian chytrid fungus, in contrast, has a very broad host range and while it is highly pathogenic in some populations of some frog species [42,43], other species (and even some populations of frogs that have declined as a result of the disease [44]) appear to be able to persist in the presence of the disease with little overt impact on either individuals or at a population level, creating the potential for spillover from tolerant reservoir species even as intolerant species become rare.…”

Electrolyte Depletion in White-nose Syndrome Bats

“…However, imbalance of blood electrolyte concentrations is known to cause serious physiologic problems (e.g., impaired neural and heart function) in other mammals, as well as in amphibians infected with skin-damaging chytrid fungus (Batrachochytrium dendrobatidis; Voyles et al, 2009). …”

Condition-dependent reproductive effort in frogs infected by a widespread pathogen

“…The primary mechanism of attracting and locating mates in most frogs is through male advertisement calls, and frog populations in many regions of the world are undergoing declines due to chytridiomycosis, the disease caused by the widespread pathogenic fungus Batrachochytrium dendrobatidis [23]. This fungus attacks the skin cells of amphibians and disrupts their osmoregulatory and transport functions, ultimately altering electrolyte concentrations in the blood, and causing cardiac arrest when the fungal population on the host reaches a high density [24]. Currently, we have very little understanding of whether B. dendrobatidis infections influence amphibian reproduction.…”