Snake Fungal Disease; another emergent fungal pathogen but what do we know about it and should we worry about it in the UK?
The chytrid fungus, Batrachochytrium dendrobatidis (Bd), and its impacts on amphibian populations worldwide have been described in terms that leave little doubt about its severity- The worst disease ever recorded in terms of biodiversity impacts. However, Bd is only one species in a range of newly described pathogens, which all are seriously affecting wildlife species and which, intriguingly, are all fungal. Froglife have written several times about the newly described chytrid species, Batrachochytrium salamandrivorans, the salamander killer fungus found in 2013 in The Netherlands and which is now spreading into Belgium and Germany and threatening newt species across Europe and North America. This new chytrid has very likely been introduced to Europe by the amphibian pet trade from Asia and has since spread into wild amphibian populations due to poor biosecurity. Yet, people interested in mammals and more specifically bats, will be able to tell you about white-nose syndrome disease (http://www.batcon.org/index.php/our-work/regions/usa-canada/address-serious-threats/wns-intro), a recently discovered fungal disease in bats, most likely transported accidentally from Europe or Asia into North America. This disease has had catastrophic impacts on hibernating bats of several species, has been spreading in Eastern USA and Canada and has killed at least 5.7 million bats there since 2006 with no signs of slowing down.
In line with these aggressive and newly described fungal pathogens, Snake Fungal Disease (SFD) is an emerging disease affecting populations of wild snakes in the eastern and midwestern United States. The clinical manifestations of SFD, typically resulting in swollen and deformed parts of the head and body, scale erosions and crusty scales, had been reported infrequently in both captive and wild snakes in the USA since at least 2002, including in at least one large mortality event in Florida, but more recently the number of recorded wild snakes showing signs of fungal dermatitis has been increasing rapidly and the disease is now known to occur in at least 16 states in the eastern USA. In 2008 laboratory analyses have demonstrated that the fungus Ophidiomyces ophiodiicola is consistently associated with SFD, often alongside additional fungi, but more recent studies have been able to cause infection showing typical SFD manifestations using only cultures of this fungal species. So far this infection has only been detected in snakes, often involving rattlesnakes, but also including water snakes and colubid snakes. Given the pattern of distribution, the fungus appears to have existed for a long time in the USA and it might persist as an environmental saprobe in soil, as well as colonizing living hosts but the reasons for the fact that it is now attacking snakes remains a mystery. Just like for other emerging fungal pathogens, many fundamental questions about the origin of O. ophiodiicola, mode of transmission, and effective treatment options are currently unknown and still need to be investigated. Has the fungus mutated and become more pathogenic, is it being made more aggressive by climate change? Has it simply been undetected for a long time due to the fact that snakes are so cryptic in the wild? All questions that need an answer but we do know that the disease has caused substantial declines in already threatened and fragmented snake populations in the USA, including the timber rattlesnake (Crotalus horridus) in New Hampshire and the Eastern Massasagua (Sistrurus catenatus) in Michigan.
Although Snake Fungal Disease has so far only been reported in the eastern parts of the USA, the evolution of other recent fungal diseases and the ever increasing possibilities for moving goods, animals including pets and pathogens between countries and continents, are all very important reasons why biosecurity measures should be carefully implemented worldwide, including in the UK, and why people involved in reptile and snake monitoring programs as well the interested general public should all be vigilant and report any incidents of disease in both amphibians and reptiles. If you see any dead or diseased amphibians and reptiles please report this to Froglife using the firstname.lastname@example.org email or directly to the Garden Wildlife Health project where Froglife are partners http://www.gardenwildlifehealth.org/.
Allender, MC, et al., The natural history, ecology, and epidemiology of Ophidiomyces ophiodiicola and its potential impact on free-ranging snake populations, Fungal Ecology (2015), http://dx.doi.org/10.1016/j.funeco.2015.05.003
Further information about the Snake Fungal Disease