Salamanders on the edge
Scientists are racing to prevent a deadly disease that kills salamanders from reaching the USA
More than 40 per cent of the world’s amphibians are currently threatened with extinction. Chytridiomycosis, an emerging infectious disease, has driven population declines of 501 amphibian species; 90 of these are now extinct. The disease is caused by two fungal pathogens, Batrachochytrium dendrobatidis (Bd), discovered in the 1980s, and the more recently discovered Batrachochytrium salamandrivorans (Bsal) – a strain particularly damaging to salamanders. With the number of European salamanders infected with Bsal increasing, herpetologists are working to prevent its introduction to salamander strongholds in the USA.
Bsal was first isolated in 2012 from a fire salamander in the Bunderbos region of the Netherlands, where the population had been mysteriously declining since 2010. In less than six months, the disease caused a 99.9 per cent drop in fire salamander populations in the Netherlands, before spreading to Germany, Belgium and Spain.
In 2014, epidemiologists at the University of Ghent, led by An Martel, showed that Bsal had probably coevolved with Asian salamanders for generations, but was introduced to susceptible European populations through the pet trade. ‘The sixth mass extinction is threatening salamanders and it’s happening because of humans and our effects,’ says world salamander expert Vance Vredenburg. He explains that pet owners can act irresponsibly, albeit with the best intentions. ‘When people move out, or get tired of looking after salamanders, they sometimes release them into the wild. If infected individuals break out, they can spread disease-causing microorganisms.’
Large declines of salamander diversity would disrupt ecosystems. Salamanders regulate food webs between aquatic and terrestrial systems; as mid-level predators, they control grazers and insects; their burrowing helps contribute to soil quality, providing tertiary consumers with energy and nutrients. North America hosts 48 per cent of the world’s 676 salamander species. Although Bsal is yet to be detected on the continent, epidemiologists fear that the international pet trade could imperil this stronghold of salamander biodiversity. Between 2010 and 2014, 779,002 salamanders arrived in the
USA from Asia through ports in Los Angeles, Tampa, New York, Atlanta and San Francisco.
Bsal is extremely difficult to eradicate in wild populations. Prevention is a more viable option. Despite the high number of species threatened, scientists remain optimistic. ‘As scientists, we’re hopeful because we’ve identified
Bsal before it has spread to the US populations,’ says Vredenburg. US legislation has been drafted quickly: the US Fish and Wildlife Service imposed a moratorium on the importation of
201 species of salamanders to the USA, effective from January 2016. Switzerland and Hungary have already banned imports. In 2018, the EU announced animal-health protection measures for internal trade, including enforced Bsal testing, quarantines and other biosecurity measures.
Yet, scientists still want to see a more substantial international effort. ‘We really need a World Health Organization for wildlife diseases. CITES is only for traded or endangered and protected species,’ says Vredenburg. He’s hoping that the world has developed a newfound recognition of the importance of epidemiology. ‘The Covid-19 pandemic in humans is a poignant example of why we need an international body to provide standardised guidance on wildlife diseases. Countries can’t solve pandemics alone; collaboration is essential.’
Once thought to be born in fires, the fire salamander is Europe’s best known salamander species