By Jonathan E. Kolby
National Geographic Explorer
PhD Candidate, James Cook University
As the world witnesses catastrophic biodiversity loss, amphibian species are among those most at risk. Already burdened by habitat destruction and pollution, hundreds of amphibian species around the world are now threatened with extinction by an emerging infectious disease. The culprit is amphibian chytrid fungus (Batrachochytrium dendrobatidis), an often highly virulent aquatic pathogen that causes the skin disease chytrdiomycosis. Severe infection often damages vital skin function and interferes with the ability to regulate electrolytes, resulting in cardiac arrest. Before this planet loses some of its most fascinating and unique creatures for good, my team of biologists, zoologist, artists and conservationists seek to give these animals a boost in their battle against chytrid.
Chytrid has now been detected in approximately 60 countries and on every continent except Antarctica. Unfortunately, this pathogen demonstrates low host species specificity and many of the worlds’ 7000+ amphibian species appear to be susceptible. Response to infection and time until death varies considerably between species, and those that do tolerate infection can act as reservoir hosts, aiding in its persistence and spread. This pathogen knows virtually no boundaries. It has been found in amphibian habitats from sea level upwards to alpine mountain peaks in remote wilderness areas, and continues to spread between countries and continents.
For the past 5 years, I’ve been studying global chytrid dispersal and exploring opportunities to reduce its spread. Chytrid is transmitted through direct skin contact between amphibians and by exposure to materials contaminated with zoospores shed from infected animals. These non-living infectious materials, also known as fomites, can include things such as water, soil, shipping containers, and footwear. Part of the reason why chytrid is an especially difficult pathogen to control is because it can survive for weeks and potentially months in the absence of a host. The international wildlife trade transports millions of amphibians annually, and my PhD thesis research has shown this to be a frequent contemporary pathway of international chytrid dispersal in the absence of targeted biosecurity regulations.
Unfortunately, no attempt to stop an advancing wave of chytrid has yet been successful and once established, it cannot be eradicated. Halting this globally emerging disease event now poses one of the greatest conservation challenges in modern times. Despite the strong link between amphibian commerce and chytrid spillover, even countries that don’t commercially import amphibians continue to become exposed, for example Madagascar. It’s possible that hitchhiking alien amphibian invaders or even tropical storms might have introduced chytrid to this island nation, but the exact source remains a mystery.
As we struggle to control the spread of chytrid, time is running out for many species on the brink of extinction, especially those in Latin America. For the past 10 years, I’ve been monitoring the long-term impact of chytrid in the cloud forest of Cusuco National Park in Honduras. In this high-elevation rainforest, I found that chytrid severely threatens three endangered frog species with extinction: 1) the Cusuco spike-thumb frog (Plectrohyla dasypus), 2) the Exquisite spike-thumb frog (Plectrohyla exquisita), and 3) the Mossy red-eyed frog (Duellmanohyla soralia). A growing number of species around the world may soon become extinct without some form of conservation intervention, but few long-term rescue methods have been successfully demonstrated. Therefore, I’m proud to announce the establishment of the Honduras Amphibian Rescue and Conservation Center (HARCC), a new platform my frog rescue team has launched from which to combat chytrid-driven extinction in Central America.
The greatest challenge to keeping amphibians alive in the wild with chytrid is that treatment for infection must be administered in a controlled environment, most often via the administration of an itraconazole bath. Even following successful treatment, amphibians do not appear to develop a significantly greater resistance to subsequent chytrid infection. After studying how chytrid affects certain endangered amphibians in Honduras, my team is fortunate to have identified a method likely to prevent extinction while allowing them to remain in their natural chytrid-positive habitat.
Chytrid appears to consistently infect younger amphibians both more frequently and severely than adults, and a large proportion of these young amphibians are unlikely to survive to adulthood. Conversely, my surveys have also shown that the “lucky” survivors that dodged the chytrid bullet as juveniles are often able to tolerate infection as adults and persist in a chytrid-positive environment. Did these animals survive because they possessed superior innate resistance to disease and if so, might this be transferred to offspring? Or could these animals have instead simply escaped chytrid exposure longer, despite equivalent susceptibility? This is an area still under investigation, but most importantly, our field data agree with recent studies that show a clear age-related association between the timing of chytrid exposure and frog survival: adult frogs survive more often than young recently metamorphosed frogs. Thus, it may be possible to protect some species from extinction in the wild by loosening this bottleneck and protecting young animals from disease through a head-start and reintroduction program based at HARCC.
HARCC is a frog rescue laboratory that we are constructing inside two ocean shipping containers in Honduras. Once fully operational, our frog rescue head-start program at HARCC will entail collecting large numbers of baby frogs from the rainforest before they die from chytridiomycosis and transporting them to our biosecure HARCC facility where we can manage their infections and boost survival. We will continue caring for them inside this safe environment until they become healthy adults with mature immune systems, at which time they will be reintroduced back into the rainforest to supplement the population of wild adults. We expect these adult frogs to survive and reproduce in the wild, and create a greater pool of offspring that will help offset the chytrid-elevated death rate of juvenile frogs. This process of collection, protection, and reintroduction year after year will help buffer against extinction. In addition, natural selection can continue searching for frogs that might be genetically resistant to chytridiomycosis and potentially build innate immunity within the populations over time. This head-start conservation method has previously been successful in assuring the survival of a variety of other wildlife species, but has infrequently been explored as a potential tool to combat chytrid.
The spread of chytrid represents one of the greatest conservation challenges the world is currently facing. Developing an effective solution will require a strong network of international communication, collaboration, and capacity building. I’m extremely hopeful that what my frog rescue team is learning in a small rainforest in Honduras may eventually save amphibians around the world from this frightening fungal foe!
My team is currently raising funds to finish building the HARCC frog rescue facility, train our Honduran staff, and begin frog rescue operations by summer 2017. If you’d like to learn more and help support this effort, please visit our project page here: Save Frogs From Extinction.
To follow our progress and read more about this exciting conservation effort, subscribe to our updates at www.FrogRescue.com and view the HARCC FrogRescue YouTube video channel here: HARCC FrogRescue. Please also follow us on Facebook and Instagram/Twitter (@MyFrogCroaked).