Download Science Advisor to the Secretary, Dr

A. Gordon Brown, DOI Invasive Species Coordinator and Liaison to the National
Invasive Species Council
Dr. Jim Tate, Science Advisor to the Secretary
DOI
Batrachochytrium dendrobatidis was first reported in 1998 by Berger et al. (Berger, et al.
1998) and described as a new genus and species in 1999 (Longcore, et al. 1999); although
it had been incorrectly identified as another fungus in 1991 (Groff, et al. 1991). This
fungus seems to be able to live in the skin of all amphibians and is more or less
pathogenic depending on the particular species (Bufo boreas is susceptible) of amphibian,
the age at which they are exposed to the pathogen and the temperatures at which the
amphibians live. Daszak et al. (Daszak, et al. 1999) considered it an emerging infectious
disease and the NSF funded two multi-institutional grants to study amphibian diseases of
which chytidiomycosis was one (http://lifesciences.asu.edu/irceb/amphibians/) with the
other being a frog virus. In 2000 a workshop was held in Cairns, Australia to promote
knowledge of this species and formulate recommendations to lessen the risk of
chytridiomycosis to wild amphibians
http://www.jcu.edu.au/school/phtm/PHTM/frogs/control.htm#quarantine.
The Berger et al paper included information on this chytrid fungus killing amphibians in
Australia and Panama, causing declines in populations and possibly extirpating 2 species.
Since that time, population declines caused by this fungus have been reported from the
Boreal toad in Colorado, the Wyoming toad in Wyoming, the mountain yellow leg frog in
the Sierra of California and numerous additional species in Central America. Specific to
the Boreal toad in Colorado, because I was the mycologist interested in isolating the
fungus to have it available for studies of population genetics—to answer the question of
whether this organism was native or introduced—I was the recipient of dead Boreal toads
sent by Mark Jones, then the Colorado Fish & Game biologist working on the boreal toad
project. I examined the skin of these toads in the process of isolating the fungus and
found a very heavy infection of Batrachochytrium dendrobatidis, consistent with the
levels I had seen in frogs that had died in controlled experiments from inoculation with
Batrachochytrium ((Nichols, et al. 2001).
Does Batrachochytrium kill Bufo boreas in Colorado? Yes, I think it does (Muths, et
al. 2003).
Retrospective studies i.e., histological preparation of skin samples from archived museum
specimens have revealed no evidence of the fungus in North America prior to 1961
(Ouellet, et al. 2005). The earliest collected museum specimen infected with B.
dendrobatidis was collected in South Africa in 1938 (Weldon, et al. 2004) in a Xenopus
frog. Xenopus frogs were exported from South Africa to North America beginning in the
1930’s (see Ché Weldon’s PhD thesis, North-West University, Pochefstroom, South
Africa 2005) because they were widely used in local hospitals to test for pregnancy. If a
woman was pregnant, injecting some of her urine into a female Xenopus laevis frog cased
the frog to ovulate. The hypothesis that Batrachochytium originated in Africa and was
transported around the world by export of frogs was neither confirmed nor disproved by a
study of its population genetics (Morehouse, et al. 2003). Analysis of the data suggest
that different isolates from North America, Panama and Australia are part of a recently
spread clone, with the definition of recently as being since the breakup of Pangea. In
other words, because frogs don’t cross oceans by themselves, this organism was probably
spread by the activity of humans. We lack optimum population genetics markers for this
organism but expect to learn more about the genetics soon because the entire genome of
this organism is being sequenced by two genome sequencing laboratories, the Broad
Institute
http://www.genome.gov/Pages/Research/Sequencing/SeqProposals/FourFungiSeq.pdf
and the DOE Joint Genome Sequencing Institute
http://www.jgi.doe.gov/sequencing/why/CSP2006/frogfungus.html.
Is Batrachochytrium dendrobatidis an invasive organism? Yes, the evidence suggests
that it is, although where it originated is still being investigated.
Does Batrachochytrium dendrobatidis move by human activity? Yes, at least in part.
For transcontinental distances it moves by human activity. It moves around the United
States and other countries by trade in frogs for scientific and culinary purposes (I isolated
several of my cultures from a frogs in the scientific trade.) Frogs scheduled to be
destroyed after use in a laboratory or schoolrooms are sometimes released (In Arizona
and California are feral populations of the African clawed frog). Because some frogs
carry this disease without ill effects or noticeable signs, carrier frogs can be released.
Concern about biologists transferring this disease have been sufficient that protocols are
in place that herpetologists (most herpetologist, we hope) voluntarily use to thoroughly
dry or disinfect their gear between watersheds
http://www.jcu.edu.au/school/phtm/PHTM/frogs/control.htm#quarantine;
http://www.mpm.edu/collect/vertzo/herp/Daptf/fcode_e.html.
Once this organism is in an area, it can spread by non-man mediated means.
Colorado biologists knowledgable about Batrachochytrium and Bufo boreas include Erin
Muths, USGS-BRD, Cynthia Carey, U. Colorado, Boulder, Mark Jones, Colorado Fish &
Game, Lauren Livo, U. Colorado, Boulder.
Joyce E. Longcore
Department of Biological Sciences
University of Maine
Orono, ME 04469-5722
Telephone: 207-581-4396
Fax: 207-581-2969
Email: [email protected]
Berger, L., R. Speare, P. Daszak, D. E. Green, A. A. Cunningham, C. L. Goggin, R.
Slocombe, M. A. Ragan, A. D. Hyatt, K. R. McDonald, H. B. Hines, K. R. Lips,
G. Marantelli and H. Parkes, 1998. Chytridiomycosis causes amphibian mortality
associated with population declines in the rain forests of Australia and Central
America. Proc. Natl. Acad. Sci. USA 95:9031-9036.
Daszak, P., L. Berger, A. A. Cunningham, A. D. Hyatt, D. E. Green and R. Speare, 1999.
Emerging infectious diseases and amphibian population declines. Emerging
Infectious Diseases 5:735-748.
Groff, J. M., T. S. Mughannam, A. McDowell, A. Wong, M. J. Dykstra, F. L. Frye and R.
P. Hedrick, 1991. An epizootic of cutaneous zygomycosis in culture dwarf
African clawed frogs (Hymenochirus curtipes) due to Basidiobolus ranarum.
Journal of Medical and Veterinary Mycology 29:215-223.
Longcore, J. E., A. P. Pessier and D. K. Nichols, 1999. Batrachochytrium dendrobatidis
gen. et sp. nov., a chytrid pathogenic to amphibians. Mycologia 91:219-227.
Morehouse, E. A., T. Y. James, A. R. Ganley, R. Vilaglys, L. Berger, P. J. Murphy and J.
E. Longcore, 2003. Multilocus sequence typing suggests the chytrid pathogen of
amphibians is a recently emerged clone. Molecular Ecology 12:395--403.
Muths, E., P. S. Corn, A. P. Pessier and D. E. Green, 2003. Evidence for disease-related
amphibian decline in Colorado. Biological Conservation 110:357-365.
Nichols, D. K., E. W. Lamirande, A. P. Pessier and J. E. Longcore, 2001. Experimental
tranmission of cutaneous chytridiomycosis in dendrobatid frogs. Journal of
Wildlife Diseases 37:1-11.
Ouellet, M., I. Mikaelian, B. D. Pauli, J. Rodrigues and D. M. Green, 2005. Historical
evidence of widespread chytrid infection in North American amphibian
populations. Conservation Biology
Weldon, C., L. H. du Preez, A. D. Hyatt, R. Muller and R. Speare, 2004. Origin of the
amphibian chytrid fungus. Emerging Infectious Diseases 10:2100-2105.