The chytrid fungus Batrachochytrium dendrobatidis (Bd) is responsible for the infectious disease chytridiomycosis that is devastating amphibian populations worldwide. Bd was first discovered in Australia in 1998 and has since spread globally, causing population declines and extinctions of over 200 frog species. While the exact origin of Bd is unknown, it likely spread through increased global trade and transport of amphibians. Climate change may also be facilitating the spread and emergence of Bd in new areas by forcing amphibians to higher elevations and latitudes. Conservation efforts include capturing wild amphibians, breeding them in chytrid-free environments, and re-releasing them to help

1. Amphibian Die Off:
Chytrid Fungi
Bio 102 Lab Case Study
Scanning electron micrograph of a
frozen intact zoospore and sporangia of
the chytrid fungus (Batrachochytrium
dendrobatidis), CSIRO from Wikipedia

2. Chytridomycosis
• Infectious disease of amphibian
caused by Batrachochytrium
dendrobatidis (Bd) (Daszak et al.
2003).
• First found in Australia in 1998
devastating amphibian populations
(Berger et al. 1998)
• Specific to amphibians
• One of two species of chytrid known
to infect vertebrates (Raphael and
Pramuk, 2007)
– Other infects fish
• Bd is spreading world wide
• Responsible for greatest disease
induced biodiversity loss in recorded
history (Skerratt et al. 2007)
– Extinction of over 200 species of
frogs
Dead Bd-infected Atelopus limosus at Sierra
Llorona (posed to show ventral lesions and
chytridiomycosis signs), photo by Brian
Gratwicke

3. New species targets salamanders

4. Questions
1. What phylum of fungi is responsible for chytridiomycosis?
2. Why is this fungi successful at killing amphibians?
3. Why be concerned about the world’s amphibian populations?
What role do amphibians play in ecosystems?

5. Origin of Bd
• Not exactly known
• Found in Xenopus laevis which
are used in labs, and
previously were important for
pregnancy testing
– Inject frog with human female
urine. If frog laid eggs a few
hours later, human female was
pregnant (Rogers, 2013)
• Also used in fishing as trade
increased
• Weldon et al. (2004) found
museum specimens with Bd
dating back to 1938

6. 1. How might Bd be spreading through the
environment?
2. Propose a hypothesis that would explain why
Bd is spreading like a new disease throughout
the world

7. How does Bd spread?
• Not exactly known, but likely human induced
• Pet trade, fishing trade, human consumption of bullfrogs, scientific
trade (Reed et al. 2005, Weldon et al. 2004)
• Pico and Collins (2008)—positive Bd water samples from bait shops
• Inadvertent through produce trade—Occurred in Tasmania in 1993
(Pauza and Driessen, 2008)
• Tree frog in a banana box in Tasmania imported from Australia was
captured and developed Bd (Obendorf 2005)
• An estimated 50,000 frogs per year are accidentally carried in
produce (McDonald and Speare 2000), and up to 70% are released
at their destination (O’Dwyer et al., 2000)
• Tasmania—associated with gravel roads sprayed with water from
wetlands, and moist soil transported (Pauza and Driessen, 2008)

8. Other scientists are
indicating that Bd
may be spreading
due to climate
change.
How might
this happen? A chytrid-infected frog, Forrest Brem

9. Climate Change and Bd
• Temperatures warm, and organisms shift
upward in elevation, or toward the poles,
especially if ponds dry up (Parmesan, 2006)
– May introduce Bd to other areas
• In Andes, deglaciation—amphibians into new
areas at record elevation, one species has Bd
with no side effects, other species Bd and die
offs (Seimon et al., 2006)

10. Figure 1. Summary of Red List
categories for all amphibians. The
percentage of species in each
category is displayed on the pie
chart (from Stuart et al. 2008)
1. Some scientists are
attempting to prevent the
extinction of amphibians by
capturing amphibians in the
wild, breeding them in
chytrid free labs, then
releasing some of the
amphibians into the wild.
Discuss how such a strategy
could save some species of
amphibians.
2. How else might we prevent
the spread of Bd throughout
the world?

11. Works Cited
• Davidson, E. W., Parris, M., Collins, J. P., Longcore, J. E., Pessier, A. P., and Brunner, J. 2003. Pathogenicity and transmission of chytridiomycosis in
tiger salamanders (Ambystoma tigrinum). Copeia 2003: 601-607.
• Berger, L., Speare, R., Daszak, P., Green, D. E., Cunningham, A. A., Goggin, C. L., Slocombe, R., Ragan, M. A., Hyatt, A. D., McDonald, K. R., Hines, H. B.,
Lips, K. R., Marantelli, G., and Parkes, H. 1998. Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of
Australia and Central America. Proceedings of the National Academy of Sciences, USA. 95: 9031-9036.
• Raphael, B., and Pramuk, J. 2007. Treatment of chytrid infection in Typhlonectes spp. using elevated water temperatures. Proceedings of the IRCEB
meeting, Phoenix, Arizona, November 2007. Unpublished.
• Skerratt, L. F., Berger, L., Speare, R., Cashins, S., McDonald, K. R., Phillott, A. D., Hines, H. B., and Kenyon, N. 2007. Spread of chytridiomycosis has
caused the rapid global decline and extinction of frogs. EcoHealth 4: 125-134.
• Weldon, C. and du Preez, L.H. 2004. Decline of the Kihansi Spray Toad, from the Udzungwa Mountains, Tanzania. Froglog 62: 2-3.
• Weldon, C., du Preez, L. H., Hyatt, A. D., Muller, R., and Speare, R. 2004. Origin of the amphibian chytrid fungus. Emerging Infectious Diseases 10:
2100-2105
• Reed, K. D., Ruth, G. R., Meyer, J. A., and Shukla, S. K. 2005. Chlamydia pneumoniae infection in a breeding colony of African Clawed Frogs (Xenopus
tropicalis). 2000. Emerging Infectious Diseases 6: 196-199.
• Picco, A. M., and Collins, J. P. 2008. Amphibian commerce as a likely source of pathogen pollution. Conservation Biology 22: 1582-1589.
• Obendorf, D. L. 2005. Developing field & diagnostic methods to survey for chytridiomycosis in Tasmanian frogs. Central North Field Naturalists, Inc.
Tasmania, Australia. Report to the Department of Environment and Heritage, Canberra. Available online.
• O'Dwyer, W. T., Buttemer, W. A., and Priddel, D. M. 2000. Inadvertent translocation of amphibians in the shipment of agricultural produce into New
South Wales: its extent and conservation implications. Pacific Conservation Biology 6:40-45.
• Pauza, M., and Driessen, M. 2008. Distribution and potential spread of amphibian chytrid fungus Batrachochytrium dendrobatidis in the Tasmanian
Wilderness World Heritage Area. Report on Amphibian Chytrid Fungus in the TWWHA, Department of Primary Industries, Parks, Water, and
Environment. Available online.
• Rogers, K. 2013. The First Pregnancy Tests and the Demise of Frogs.Encyclopedia Brittanica. http://blogs.britannica.com/2013/05/the-first-
pregnancy-tests-and-the-demise-of-frogs/
• Seimon, T. A., Seimon, A., Daszak, P., Halloy, S. R. P., Schloegel, L. M., Aguilar, C. A., Sowell, P., Hyatt, A. D., Konecky, B., and Simmons, J. E. 2006.
Upward range extension of Andean anurans and chytridiomycosis to extreme elevations in response to tropical deglaciation. Global Change Biology
12: 1-12.
• Parmesean, C. 2006. Ecological and Evolutionary Responses to Recent Climate Change. Annual Review of Ecology, Evolution, and
• Systematics 37:637–69.
• Stuart, S.N. et al. (2008). Threatened Amphibians of the World. Barcelona/Gland/Arlington: Lynx Edicions/IUCN/Conservation International.