Emerging infectious diseases as a threat to wildlife – the case of the salamander plague

Emerging infectious diseases pose an increasing threat to global biodiversity. Amphibians especially suffer from spreading fungal skin diseases. One is the salamander plague, caused by the chytrid fungus Batrachochytrium salamandrivorans (Bsal). Bsal is native to Asia and is invasive in Europe. It primarily affects caudate amphibians (salamanders and newts). Currently, Bsal outbreaks are known in the wild from > 100 sites in Belgium, Germany, Spain, and the Netherlands. First discovered in 2010, the salamander plague mainly affects the European fire salamander, in which it causes dramatic population declines with mass mortalities. Given the strong virulence of Bsal, it remains misunderstood, however, that fire salamanders still exist at outbreak sites and in some cases reproduce (although in low numbers). Explanations range from previously uninfected animals to possible resistance. For other caudates, even less is known about the impact. While the decline of the northern crested newt may be related to Bsal, the Alpine newt in particular is considered tolerant and thus a Bsal reservoir and vector. Similarly, the midwife toad can become infected with Bsal and recover without symptoms. However, nothing is yet known about possible sublethal effects in these vectors. The Alpine salamander so far seems unaffected by Bsal spread.

Germany is a Bsal ‘hotspot’ with 90% of all sites, located in Bavaria, North Rhine-Westphalia and Rhineland-Palatinate. In this country, Bsal was first detected in 2015 in the northern Eifel region in the course of monitoring, although a very first outbreak occurred here as early as 2004 due to old material examined in retrospect. In the meantime, other Bsal regions include the southern Eifel (first detection in 2017); the Ruhr area (first detection in 2017) with the adjacent regions Bergisches Land and Sauerland; the Steigerwald (first detection in 2020) and the Allgäu (first detection in 2020). It is undisputed that Bsal is spreading further, but dispersal speed and mechanism remain little understood. Besides amphibians, other wildlife could play a role as vectors. In long distance dispersal, humans should not be underestimated as potential carriers. It must also be considered that the occurrence of salamander plague in the different regions could also be due to independently occurring entries.

The salamander plague poses a serious threat to the amphibian diversity of the western Palearctic. This emphasizes how serious emerging infectious diseases should be taken.