Epidemiological tracing of Batrachochytrium salamandrivorans identifies widespread infection and associated mortalities in private amphibian collections

Abstract

The amphibian chytrid fungus Batrachochytrium salamandrivorans (Bsal) infects newts and salamanders (urodele amphibians), in which it can cause fatal disease. This pathogen has caused dramatic fire salamander population declines in Belgium, the Netherlands and Germany since its discovery in 2010. Thought to be native to Asia, it has been hypothesised that Bsal was introduced to Europe with the importation of infected amphibians for the commercial pet trade. Following the discovery of Bsal in captive amphibians in the United Kingdom in 2015, we used contact-tracing to identify epidemiologically-linked private amphibian collections in Western Europe. Of 16 linked collections identified, animals were tested from 11 and urodeles tested positive for Bsal in seven, including the identification of the pathogen in Spain for the first time. Mortality of Bsal-positive individuals was observed in five collections. Our results indicate that Bsal is likely widespread within the private amphibian trade, at least in Europe. These findings are important for informing policy regarding Bsal control strategies.

Figure 1

Epidemiological links between all sixteen contact-traced private collections. Access was granted to Collections (A-K) with all urodeles swabbed for Bsal infection. Access was not granted to Collections (L-P). Arrows indicate the direction of transit of animals, including those subsequently identified as Bsal-positive. Numbers and percentages indicate the number of Bsal-positive/total number of urodeles tested.

Figure 2

Section of hindlimb digit from a Lissotriton boscai euthanased on welfare grounds from Collection A (stained with haematoxylin and eosin). Black arrow indicates an epidermal erosion. Fungal zoosporangia (circled) are visible throughout the epidermis.