Emerging Infectious Disease and the Trade in Amphibians

Amphibians are the most threatened class of vertebrate, and rates of species decline and extinction far exceed those seen historically. Habitat loss, climate change, over-exploitation and emerging infectious disease have all been identified as threatening processes. The trade in amphibians has been implicated in over-exploitation through the harvesting of wild animals, and as an important pathway for the global spread of the fungal pathogen, Batrachochytrium dendrobatidis (Bd). However, there are no analyses of how Bd may spread through the trade chain. This thesis addresses this issue by (1) determining the prevalence of Bd at different stages of the trade chain; (2) examining knowledge, husbandry protocols and biosecurity among retailers and (3) assessing the risk of Bd dissemination into the wild in the UK.

Approximately 20,000 amphibians from at least 11 countries enter the UK annually via Heathrow Animal Reception Centre. Overall Bd prevalence was 3.6%, but was confined to six of the 43 genera encountered, and only detected in shipments from the USA and Tanzania. Amphibians were sold by 30% of the estimated 3500 livestock retailers in the UK, but made a low contribution to overall income. Disease awareness and knowledge in retailers was found to be lacking, although husbandry standards were deemed to be appropriate. Mortality appeared to be influenced by restocking methods and number of species held, but mass die-offs as a result of disease were generally uncommon. Screening of over 2000 amphibians from 148 retailers for Bd revealed a prevalence of 5.8%, but the geographic distribution of infection in the UK was patchy, and was more prominent in aquatic species. A risk assessment conducted according to the framework set out by the World Organisation of Animal Health, identified regions and sections of the trade that pose the greatest threats in terms of introducing Bd, and assessed various mitigation measures. The consequences of novel strains of Bd and a second, recently discovered Batrachochytrium species were found to pose a risk to both native UK and captive amphibians. As trade bans are unlikely to be feasible or effective, alternative measures to mitigate the impact of disease are evaluated.