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 US.
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 under six months, the disease caused a 99.9 per cent drop in fire salamander populations in the Netherlands, later spreading to Germany, Belgium and Spain.
In 2014, epidemiologists at the University of Ghent, led by An Martel, showed that Bsal had probably co-evolved 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 676 salamander species worldwide. Although Bsal is yet to be detected in North America, epidemiologists fear that the international pet trade could imperil this stronghold of salamander biodiversity. In 2015, one study identified the most likely entry points of Bsal into the US from Asian markets. Between 2010 and 2014, 779,002 salamanders arrived in the US from Asia through ports in Los Angeles, Tampa, New York, Atlanta and San Francisco.
Bsal in wild populations is extremely difficult to eradicate. Prevention is a more viable option. Despite the high number of species threatened, scientists are remaining optimistic. ‘As scientists, we’re hopeful because we’ve identified Bsal before it has spread to the US populations,’ says Vredenbrurg. US legislation has been built quickly: the US Fish and Wildlife Service (UFWS) imposed a moratorium on the importation of 201 species of salamanders to the US, effective from January 2016. To control the infection in Europe, 17 scientists and 27 nature organisations sent a letter to the European Commission asking for the same ban to be enforced. Switzerland and Hungary have already banned imports. In 2018, the EU announced animal health protection measures for intra-Union trade, including enforced Bsal testing, quarantines and other biosecurity measures.
Heightened public awareness will also be critical to safeguarding wild populations. The European Commission has recently established BsalEurope, a public awareness and case-reporting campaign. Vredenburg has also co-founded the public resource AmphibiaWeb which is building awareness of Bsal among scientists and hobbyists. ‘Public awareness is being built. At the same time, scientists can rapidly share disease data online to avoid lags with publishing, so we’re on the right track,’ says Vredenburg.
Yet, scientists still want to see more international effort. ‘We really need a World Health Organisation for wildlife diseases. CITES is only for traded or endangered and protected species,’ says Vredenburg. He’s hoping that the world has a newfound recognition for 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.’