Humans are not the only group of organisms we as a species have to be concerned about. In addition to the impact our direct actions have on the environment around us, there is also the natural interplay between pathogens and wild species that may be exacerbated by the global nature of human travel. That is especially so for small organisms like bacteria or fungi that could easily be accidentally taken to other countries by unaware tourists or shipping transports.
Countries around the world have already seen the deadly impact of invasive species on the local ecosystems, with practically every large nation having some sort of invasive conflict being dealt with. And we have also found that often once such a species has spread to a new region, it is practically impossible to remove it. Our efforts at such critical points are mere stopgaps, rather than cures for the infestations.
In a collaboration between the American Museum of Natural History, the US Geological Survey, and a scientist from the University of Maryland, it has been discovered that a new threat is emerging to threaten snakes in particular. Not any specific species of snake, but all snakes.
This emerging infectious disease (EID) has been termed snake fungal disease (SFD) and is caused by the fungus Ophidiomyces ophiodiicola. As you can tell by the name (based on the clade that snakes are taxonomically included in, Ophidia), this fungus has been snake focused from the beginning. It is the only known fungal species in its genus.
First described in 2009 and genetically identified in 2013, this fungus has been spreading like a wildfire through North America and possibly beyond, as snakes have proven difficult to find, catch, and test for this disease. Very recently, three species of snakes in Europe were also announced to have tested positive for the fungus, showing that it has already hopped continents and oceans.
Previously, it was detected in 23 species across the eastern United States, in a perceived variety of environments and among a wide taxonomic swath of the Ophidia clade. Once it has invaded its host, the fungus has been shown to cause lesions on the body of the snakes, especially on the head. Molting has the possibility to remove these, but the symptoms as a whole have caused a number of deaths and one side effect is rapid skin shedding that can cause a loss of physical energy.
Even worse, the fungus appears to alter the behavior of the infected snakes and causes them to spend greater amounts of time basking in the sun, even while hungry or thirsty. Thus, this not only puts them at risk of starvation, but also increases the time that they are exposed to attacks from predators.
With all of this considered, the researchers wanted to model and test the dispersion and phylogenetic susceptibility of snake species to the fungus. There were several possibilities of outcome. If the species found to be infected were still within the same overall taxonomic grouping, then that could imply that the fungus is isolated to only the snakes that fall within the circle of that group. That would be the most ideal result. Alternatively, it could be that the phylogeny is dispersed and the environments are ultimately not actually that different, which would imply that the fungus targets snake species with particular traits, allowing other susceptible species to be modeled and contained.
Third, the phylogeny could be narrow, but the environments variable, implying that the fungus targets species that are in specialized competitive niches. And then fourth, the worst option, it could be that there is no pattern at all and the infected species are completely random.
To find out which is the actual answer, the researchers plugged in all the available taxonomic and genetic data on the infected species into the model they had built. Groupings were made for comparison between just those in the US, those in Europe, and then all of them globally. A set of traits were also added to the model to see if the fungus targets any outstanding type specifically. These traits included “habitat preference, parity, average clutch size, diel pattern, diet, and maximum body size”.
The last step was to program the model to do a comparison between the phylogenetic data and the trait specific data to see if there was any correlation. They found…nothing.
The Worst Case
The result of their model is that the fungus appears to fall under the dreaded fourth option, where the phylogenetic and ecological dispersion of the species it infects are completely random. The only found correlation of what the fungus targets is that of “is the target a snake?”.
Due to this, the scientists concluded that all 98 species of snake in the US are susceptible to the fungus. Every single one is at risk. And probably most, if not all, of the other snake species in the world too.
The researchers suggest that prevention efforts should focus on direct containment of the fungus’ spread and not on trying to identify where it will jump to next. Because it could jump to any other snake species, so there is no way to map it directionally. There is no taxon or environmental bias in its expansion, so those should be thrown out of prevention efforts as well.
A detriment to these efforts is that we are still not aware of how the fungus transfers from one host to the next, its method of transmission is unknown. So utmost care must be taken when dealing with or moving infected snakes, because any part of their scales, bodily fluids, or anything else could be the method of transmission.
Scientific Vigilance For Snakes
Regardless, the fungus is quickly reaching the level of a environmental pandemic crisis and, if too many snakes are lost, the effects could ripple out disastrously into other parts of the food chain. The only saving grace is that the lethality of the fungus is currently not significantly high. Even so, snake species are paramount to pest management in the wild and an explosion of rodent populations from just a slight dip in snake communities, as one example, could bring with them an unknown army of other diseases to deal with.
Much is still to be learned about snake fungal disease and the fungus Ophidiomyces. Its physical characteristics, life cycle, and variable lethality to snakes need to be researched and described as soon as possible. Recovery from the fungus appears to be just as common as death, but the downstream effects have yet to be investigated, so there is still work to be done.
Photo CCs: Closer Look (6145095297) from Wikimedia Commons