Amphibian chytridiomycosis, caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), is an emerging infection that has caused the rapid decline or extinction of more than 200 amphibian species across the world. Bd infects the keratinized epidermis of metamorphosed amphibians as well as the tooth rows and jaw sheaths of anuran larvae. Mortality occurs when the pathogen disrupts cutaneous osmoregulatory function, leading to electrolyte imbalance in susceptible amphibians. Mass mortalities and declines of amphibian populations have been documented in North America, Central America, Europe and Australia leading to extirpations of up to 40% of species in affected areas. Consequentially, Bd is now an internationally notifiable disease and reporting is now obligatory for signees to the World Organisation for Animal Health legislation.

While the origin of Bd remains unclear, increasingly the global trade in amphibians is associated with the spread of the infection. Global samples of Bd genotypes from previously unsampled regions are essential to test this hypothesis. Professor Yiming Li’ team presents a study of the prevalence and phylogeny of Bd in both invasive and native amphibian species in markets and in the wild in ten provinces of China. The researchers used a nested PCR assay to amplify the ribosomal internal transcribed spacer region of Bd followed by sequencing. Their results showed 246 of 2734 amphibians testing positive for Bd, with 157 positive samples in the wild (7.6 %) and 89 in markets (13.5%). 30 haplotypes of Bd were identified, including 20 first detections. Introduced Lithobates catesbeianus had the highest prevalence of infection and the largest number of Bd haplotypes in both the wild and markets. Phylogenetic analysis based on 73 haplotypes (57 from Asia, 16 from other continents) showed that a unique, well supported, basal haplotype is present in Asia. Phylogeographic analyses revealed some geographic structure exists amongst a subset of global haplotypes. They found that strains of the basal haplotype infected Babina pleuraden, an amphibian that is endemic to China, and Andrias japonicus, endemic to Japan, showing that Southeast Asia harbors a novel endemic lineage of amphibian-associated Bd. The results suggest that Bd in Asia pre-dates the expansion of a globalised lineage of Bd, a finding that is indicative of a broader association of amphibians and chytrids than has previously been recognized. More genetic datafrom Bd isolates are needed to reveal the phylogenetic relationship of Bd in China compared to that found elsewhere.