Spore Our Shores: Amphibian Fungal Infection- Are We Next?
For the past decade, there have been growing concerns over a novel and deadly chytrid fungal infection that targets amphibians- Batrachochytrium salamandrivorans (Bsal). The fungus is already well-established in Europe, where it has resulted in the catastrophic decline of numerous salamander species. A cousin of Batrachochytrium salamandrivorans, Batrachochytrium dendrobatidis (Bd), has been a pathogen of grave concern here in the United States. It has decimated over 200 species of frog, even resulting in the extinction of several affected species (Cornell Wildlife Health Lab, 2018). Having witnessed the destruction Bd has caused in North America, researchers and wildlife officials are wary of the further devastation that could take place if Batrachochytrium salamandrivorans were to arrive here from Europe.
Part of what makes this fungus such an effective pathogen is that one of its main modes of spread is by water. Amphibians cannot survive without periodic contact with water, so they are severely at risk for developing a chytrid infection once the fungus is present in the water systems of their habitat. Bsal thrives in waters between 17 and 25℃ and can survive for up to 31 days (More et al, 2018). Spread of Bsal spores could potentially be facilitated by non-amphibian hosts, with particular concern being paid to aquatic mammals such as otters and waterfowl. However, there has not been evidence of direct infection of amphibians via contact with birds or mammals. The concern is more that the animals, who can travel much longer distances than amphibians themselves, will bring spores with them from a contaminated water source and introduce new infections to previously healthy waterways (More et al, 2018).
Bsal can also be spread by direct contact with the spores from interactions with an infected amphibian. The inter-continental spread of Bsal is a very real and worrying threat to vulnerable native amphibian populations across the globe. The most likely vector for the potential spread is the exotic pet trade, which is notorious for introducing new diseases to places where they have never been documented before. Cross-species, and more significantly, cross-taxonomic group infections are certainly possible, and made more likely if wild-caught specimens are housed in close quarters, such as during transport for sale. Clinical studies were able to isolate Bsal from Cuban tree frogs (Osteopilus septentrionalis) and then infect newts with the fungus, generating a disease response (Towe, 2021). Further complicating the issue, a simple quarantine period to check for signs of infection with the fungus prior to sale may not be an effective mitigation strategy. Bsal has been detected in captive collections of salamanders, with many Bsal-positive specimens not showing clinical symptoms of infection, classifying them as asymptomatic carriers (Sabino-Pinto, 2018). Therefore, in order to prevent the spread of the disease, all imported amphibians would have to be tested for Bsal prior to sale or cohabitation with others, which could prove logistically difficult and expensive.
Looking at case studies from Europe, experts may be able to predict the scale of disruption to native ecosystems we can expect should Bsal arrive here in the United States. One study exposed a number of species of salamander native to the Iberian peninsula to Bsal spores in a laboratory setting and observed their response. The researchers found a relatively significant discrepancy among species’ responses to Bsal infection and determined that there was a phylogenetic component to this variation (Bosch, 2021). This allowed researchers to extrapolate the susceptibility of salamander species for whom little data is available. By looking at how the close relatives of a given species fared, researchers were able to give an estimate as to whether the species in question would be highly susceptible to Bsal infection, or if it could have a decent chance at surviving the fungal attack. Similar studies could be performed with native North American amphibians to gain a better understanding of the vulnerabilities of our ecosystems. Overall, the study estimated high susceptibility for five native Iberian salamander species, intermediate susceptibility for four, and low for two. These findings show that while the threat of Bsal is large and should be vigilantly monitored, it is perhaps not quite a blanket mass mortality event waiting to happen. Unfortunately, the study also discovered that two species of salamander invasive to the region, when subjected to laboratory Bsal infection trials along with the native species, showed lower susceptibility to disease (Bosch, 2021). If this pattern were to repeat itself, it could indicate that invasive amphibians could serve as asymptomatic carriers and facilitate the spread of the fungus, in addition to the other negative impacts invasive species have on native populations.
It seems almost inevitable that Bsal will make its way to our shores. In the modern age of globalization, we are more interconnected than ever. The recent COVID-19 pandemic showcased just how quickly human pathogens can spread across the globe. While the spread of animal diseases is certainly slower, the resiliency and destructiveness of this fungus will make it much harder to eradicate it from the environment once it has taken root. The fate of North America’s amphibian population will depend heavily on the integrities of animal importers and the diligence of wildlife agencies.
Works Cited
Bosch, J., & al. (2021). Batrachochytrium Salamandrivorans Threat to the Iberian Urodele Hotspot. Journal of Fungi, 7(8). Article 644. doi:10.3390/jof7080644.
(2018, March 21). Chytridiomycosis. Cornell Wildlife Health Lab. https://cwhl.vet.cornell.edu/disease/chytridiomycosis
More, S., & al. (2018). Risk of survival, establishment and spread of Batrachochytrium Salamandrivorans (BSAL) in the EU. EFSA Journal, 16(4). https://doi.org/10.2903/j.efsa.2018.5259
Towe, A. E., & al. (2021). Batrachochytrium salamandrivorans Can Devour More than Salamanders.Journal of wildlife diseases, 57(4). doi:10.7589/JWD-D-20-00214
Sabino-Pinto, J., & al. (2018). Asymptomatic Infection of the Fungal Pathogen Batrachochytrium Salamandrivorans in Captivity. Scientific Reports, 8(1). doi:10.1038/s41598-018-30240-z.
