A deadly disease that slowly eats the skin of living frogs and salamanders is responsible for the decline or extinction of at least 501 amphibian species, according to researchers who claim it鈥檚 responsible for the greatest documented loss of biodiversity by a single pathogen.
The new study, , is the culmination of a comprehensive survey by 41 researchers from around the world.
The academics examined decades-worth of data from the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, peer-reviewed literature, and experts in the field to determine that a microscopic aquatic fungus is responsible for a dramatic decline of hundreds of amphibian species in the last half-century.
鈥淚t鈥檚 a very large number. We have records of pathogens since the time of the dinosaurs, and without question, this is the deadliest disease that has ever struck wildlife in all time,鈥� Luis Felipe Toledo, a professor at the University of Campinas's Biology Institute in Brazil and a co-author of the study, said in a press release.
According to the study, the infectious disease affecting frogs, toads, salamanders, and newts is called chytridiomycosis and is caused by two fungal species, Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal).
The pathogen is able to penetrate the amphibians鈥� skin, which then degrades and prevents them from breathing and regulating their water levels. Eventually, the infection can lead to heart failure in the infected species, the study said.
Because the disease is typically slow to kill its victims, there is a greater chance the fungus will be spread from one amphibian to the next.
To make matters worse, the lethal pathogen is remarkably adept at spreading through contact or by water. The spores of the disease have the ability to swim short distances and can even live outside of a host for weeks, months, or even years at a time before it infects.
鈥淭he main victims are the species with a limited geographic distribution, large bodies, habitats in waterlogged areas, and perennial aquatic habits,鈥� the study said.
Global spread
According to the research, the fungal species likely originated in Asia, where it currently exists in harmony with amphibian species there, before it was spread around the world by human activity, such as trade and war during the last century.
The chytrid fungus has since caused massive die-offs of frogs, toads, salamanders, and newts in the tropical regions of Australia, Central and South America and to a lesser extent in Europe, Africa, North America, and Asia where the number of diseased species is 鈥渞emarkably low.鈥�
Of the 501 affected species, the researchers note that 91 of them have become completely extinct in the wild while another 124 species have declined by more than 90 per cent.
鈥淲e consider this quantification conservative. The pathogen has probably caused the decline of many other species unknown to science,鈥� Benjamin Scheele, the first author of the study and a postdoctoral fellow at Australian National University, said.
From the known data, the academics determined the peak die-off period for amphibian populations was during the 1980s 鈥� years before the disease was discovered in 1998.
However, researchers said it鈥檚 difficult to know exactly how many species have been affected by the disease because they didn鈥檛 have enough data about earlier die-offs in the 1950s and 1960s to include them in the study.
The study鈥檚 authors compared the pathogen to other destructive invasive species, including rodents and cats. They also claimed the number of deaths associated with the disease is greater than other high-profile wildlife diseases, such as white-nose syndrome in bats, and West Nile virus in birds.
Species at risk
Because it鈥檚 so contagious and indiscriminate in selecting its victims, the disease may already be too difficult to contain in the wild, the researchers said.
Instead, the study鈥檚 authors are advising governments to take action to better protect amphibian species against current threats to their habitat, such as invasive species. The researchers are also encouraging the continuation of captive-breeding programs to maintain populations of at-risk species.
The researchers also recommend increased vigilance to curtail the trade of wild amphibians. It鈥檚 believed the pet trade has greatly contributed to the spread of the fungal disease in regions where the pathogen was previously unknown.
鈥淓ffective biosecurity and an immediate reduction in wildlife trade are urgently needed to reduce the risk of pathogen spread,鈥� the study states.
Promisingly, there are early indications of recovery among certain affected species. Of the 292 surviving species included in the study, 60 (20 per cent) of them have showed some signs of recovery.
鈥淕iven that the possibility of mitigating chytridiomycosis in the wild remains uncertain, new research and intensive monitoring with emerging technologies are necessary to identify mechanisms of species recovery and develop new mitigation actions for species in decline,鈥� Scheele said.
