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US Fish & Wildlife Service FieldNotes

CA/NV FISH HEALTH CTR: Center Assists With Amphibian Disease Surveys

Region 8, September 30, 2009
USGS researcher Black Hossack demonstrates swabbing the skin of a boreal toad to detect the amphibian chytrid fungus.(Photo courtesy of USGS website)
USGS researcher Black Hossack demonstrates swabbing the skin of a boreal toad to detect the amphibian chytrid fungus.(Photo courtesy of USGS website) - Photo Credit: n/a
Rocky Mountain tailed frog (Ascaphus montanus. (Photo courtesy of Stephen Corn, USGS)
Rocky Mountain tailed frog (Ascaphus montanus. (Photo courtesy of Stephen Corn, USGS) - Photo Credit: n/a
Leopard frog (Rana pipiens). (Photo courtesy of Blake Hossack, USGS)
Leopard frog (Rana pipiens). (Photo courtesy of Blake Hossack, USGS) - Photo Credit: n/a

by Kimberly True, California/Nevada Fish Health Center
Batrachochytrium dendrobatidis is a parasitic fungus, causing the disease Chytridiomycosis in amphibians. The disease is responsible for population declines in many parts of the world, and extinctions of several amphibian species (1-4). Commonly referred to as Chytrid, the fungus was thought to be free-living saprophytes primarily infecting vertebrates and vascular plants, but in 1999 the fungus was found to be infectious in amphibians, and the cause of mortality observed in amphibian populations in Arizona.

In order to address this emerging amphibian disease, the California-Nevada Fish Health Center (CA-NV FHC) adapted standard techniques used in fish health disease surveys such as virology, Quantitative Polymerase Chain Reaction (QPCR), and histology in order to assist researchers in assessing the presence and distribution of amphibian diseases in several regions of the United States.

The sampling technique involves swabbing an amphibian’s ventral surface, taking non-lethal toe clips or dissecting mouthparts from tadpoles.  In the laboratory, DNA is extracted from the samples and probed for the B. dendrobatidis organism using molecular methods that are extremely sensitive and capable of detecting a single fungal zoospore.  The assay not only detects the actual genetic sequence of this specific fungus but also reports the quantity of zoospores detected on the surface, or in keratinized tissue, of amphibians.  Therefore QPCR is very useful in determining the level of infection at a particular sample site, geographical region, or within a specific species being tested.

From 2008-2009, we examined over 600 samples submitted by partners from Rutgers University in New York, Arcata Fish & Wildlife Office in northern California, and USGS researchers from the Northern Rocky Mountain Science Center.

Rutgers University submitted 124 northern leopard frogs (Rana pipiens) from sites in Long Island. They were tested by QPCR and 5.5% were positive for B. dendrobatidis and this was the first reported case in leopard frogs in New York State.  This finding is helping our research partner better understand the causes of poor survival in metamorphosing amphibians that had been observed in the Long Island area. 

Working with USGS researchers from California, Oregon, Idaho and Montana, over 250 amphibians belonging to the Ascaphus genera, the Coastal Tailed frog (Ascaphus truei) and the rocky mountain tailed frog (A. montanus), were examined for Chytrid (5).  The researchers were interested in testing the hypothesis that amphibian species residing in high elevation aquatic habitats, termed headwater streams, would be susceptible to Chytridomycosis. The samples were tested by QPCR and 15% were positive for Chytrid fungus.  As part of this study, the Arcata Fish and Wildlife Office submitted 59 coastal tailed frogs (Ascaphus truei) collected in California headwater streams for testing; all samples from this geographical area were negative for Chytrid fungus. 

The nine Fish Health Centers across the country are uniquely poised to assist with aquatic animal disease testing, in particular amphibian disease surveys for Ranavirus and Chytrid fungus.  The microbiological and molecular techniques currently in use to monitor fish health are easily adapted to testing for similar types of organisms in amphibian populations.  With additional support from the fish health centers, non-lethal amphibian disease monitoring can help us better understand the distribution and prevalence of these emerging amphibian diseases.

Reports for amphibian testing are found under the National Wild Fish Health Survey section of our website, http://www.fws.gov/canvfhc/reports.asp. For more information, contact Kimberly True by email Kimberly_True@fws.gov or by phone (530)365-4271 extension 201. 

References

1. Brem, F., J. R. Mendelson III, and K. R. Lips. 2007. Field-Sampling protocol for Batrachochytrium dendrobatidis from living amphibians, using alcohol preserved swabs. Version 1.0 (18 July 2007). Electronic document accessible at http://www.amphibians.org Conservation International, Arlington, Virginia, USA.

2  Daszak, P., L.Berger, A.A. Cunningham, A.D.Hyatt, D.E.Green, R.Spears. Healthy Coastal Tailed Frog (Ascaphus truei). 1999. Emerging infectious diseases and amphibian population declines. Emerging Infectious Diseases 5(6), Centers for Disease Control.

3. Carey, C. 2000. Infectious disease and worldwide declines of amphibian populations, with comments on emerging diseases in coral reef organisms and in humans. Environmental Health Perspectives 108 (1).

4. Collins, J.P., J. Brunner, V. Miera, M. Parris, D. Schock, and A. Storfer. 2003 Ecology and evolution of infectious disease, p. 137–151. In: R. Semlitsch (ed.). Amphibian conservation.Smithsonian Institution Press, Washington, DC

5. Hossack, B.R., M.J Adams, E.H.Campbell Grant, C.A.Pearl, J.B. Bettaso, W.J. Barischivich, W.H. Lowe, K.True, J.L. Ware and P. S. Corn. in press. Journal of Herpetology.

Contact Info: Kimberly True, 530-365-4271 x201, Kimberly_True@fws.gov