Novel chytrid pathogen variants and the global amphibian pet trade.

Global wildlife trade spreads emerging infectious diseases that threaten biodiversity. The amphibian chytrid pathogen Batrachochytrium dendrobatidis (Bd) has caused population declines and species extinctions worldwide except in Asia. Fire-bellied toads (Bombina orientalis), exported in large numbers from Asia, are tolerant of Bd and carry hypervirulent ancestral chytrid BdAsia-1 variants. We assayed the virulence of a new isolate of BdAsia-1 on the model Australasian frog host Litoria caerulea. Infected individuals (n = 15) all showed rapid disease progression culminating in death, whereas sham-inoculated individuals (n = 10) presented no clinical signs of disease and all survived (log rank test, χ 2 = 15.6, df = 1, p < 0.0001). The virulence of the new isolate of BdAsia-1 is comparable to the one we assayed previously (χ 2 = 0.0, df = 1, p = 0.91). Internationally traded wildlife, even when they appear healthy, can carry hypervirulent variants of pathogens. Once new pathogen variants escape into the environment, native species that have had no opportunity to evolve resistance to them may perish. Our study suggests that hypervirulent pathogens are being spread by the international pet trade. Notifiable wildlife diseases attributable to locally endemic pathogens often fail to generate conservation concern so are rarely subject to border surveillance or import controls. Because of the danger novel variants pose, national border control agencies need to implement disease screening and quarantine protocols to ensure the safety of their endemic fauna.