Frogs and Chytrid Fungus
Chytridiomycosis of Limosa Harlequin Frog
Photo by: Brian Gratwicke, 2011
Amphibian populations today are having a hard time keeping their numbers stable. They have always faced an onslaught of problems including pollution, habitat loss, invasive species, climate change, and harvest for both the pet and food trades. Since the turn of the 21st century a new battle has begun for our amphibious friends, as new diseases like ranavirus and chytridiomycosis accelerate the global decline of amphibian species.
Amphibian populations require quality wetland and terrestrial habitat to thrive. They are unique in that they can breathe and absorb oxygen through their moist, permeable skin. A great evolutionary trait, but permeable skin also makes it much easier for harmful substances to be absorbed. These environmental sensitivities make frogs an ideal indicator of environmental stress, but now one-third of amphibian species are on the verge of extinction.
In 2001 over 1800 amphibian species were found to be globally at risk under the International Union for Conservation of Nature’s (IUCN) Red List with designations as either Vulnerable, Endangered, or Critically Endangered (IUCN, 2001). Chytrid fungus is thought to be one of the main contributing factors to this global decline, which is now being hailed as more severe and more rapid than declines of threatened bird and mammal species combined (Stuart et al, 2004)!
The California Center for Amphibian Disease Control (CCADC) states that chytridiomycosis, caused by chytrid fungus spores, directly affects frog’s water uptake and respiration through their permeable skin. Though not always present, visual symptoms can include the reddening and weakening of the skin, convulsive extension of the hind legs, and occasional small ulcers or hemorrhages (CCADC, 2007). Better indicators of sick frogs are the changes in behavior. Infected frogs were found to act lethargic, failed to seek shelter or flee when predated, were unable to right themselves if flipped over, developed abnormal posture (e.g. sitting with the hind legs away from the body), and sadly, often succumbed to a sudden death (CCADC, 2007).
But why is chytrid fungus dooming our froggy friends now? Chytrid fungi have been present in the environment for over 400 million years (Speare, 2007). The oldest report of a chytrid fungus infection came from testing African clawed frogs (Xenopus sp.) and, due to their widespread use in the pet trade, is now considered one possible vector of the fungi’s global spread (Speare, 2007). However, other studies suggest that the fungus has been present in the Americas for decades, making it unclear what exactly is triggering chytridiomycosis (Speare, 2007).
African Clawed Frog
Photo by: Brian Gratwicke, 2012
Astonishingly enough, chytridiomycosis is now found infecting amphibians on every continent except Antarctica. A recent study by the University of Calgary has extraordinarily found the fungi surviving through the cold winters of the Northwest Territories, Canada, in populations of wood frogs, boreal chorus frogs, and western toads (Schock , 2009)!
Can you imagine a future where our children can only see amphibians through the glass of an isolated quarantine room? This is the reality for many frog species already, only surviving through specialized breeding programs that keep them safe from infection until a cure can be found.
With such a quick spreading and hardy disease, what can you do to help stop the spread?
- Keep your outdoor gear clean! – clean boots and camping equipment of soil and allow to dry completely before visiting wetland areas.
- Plan to wash and dry vehicles (including tires) before entering natural areas.
- Dispose used or possibly contaminated water as far as possible from creeks, rivers, ponds and lakes.
- Avoid transferring aquatic plants, water, soils and animals between habitats (for example nursery plants, wet fill, fish and of course frogs).
- Donate to organizations involved in protecting amphibians and studying chytrid fungus.
- Do not release pet amphibians or allow these pets to come into contact with other amphibians.
Protect amphibian ecosystems and populations! You can help stop the spread of chytrid fungus!
For more information:
International Union for Conservation of Nature (IUNC). 2001. IUCN Red List Categories and Criteria. Gland, Switzerland. Accessed January 12, 2013. http://www.iucnredlist.org/initiatives/amphibians
Schock, D., Ruthig, G., Collins, J., Kutz, S., Carriere, S.2009. Amphibian chytrid fungus and ranaviruses in the Northwest territories, Canada. Diseases of Aquatic Organisms. 92:231–240.
Speare, R. 2007. Amphibian Chytridiomycosis: an informative brochure. James Cook University, Australia, Accessed January 12, 2013. http://ccadc.us/docs/AmphibianDiseaseBrochure.pdf
Stuart, S., Chanson, J. 2004. Status and trends of amphibian declines and extinctions worldwide. Science 306; 1783-1786.