genefish - cab3

A brief review of the deadly frog fungus Bactrachochytrium dendrobatidis, recently indicated in deaths of two Washington state endangered species, Rana (=Lithobates) pipiens and R. pretiosa

Globally, amphibians are the most rapidly declining vertebrate group (Stuart et al. 2004), with declines linked to (but not limited to) habitat destruction, overexploitation, environmental change, and a pathogen Batrachochytrium dendrobatidis (reviewed by Stuart et al. 2004, Skerratt et al. 2007). First described in 1998, Bactrachochytrium dendrobatidis (Bd) has and is affecting amphibian populations globally (Figure 1).Rapid d

Figure 1. Global distribution of Bactrachochytrium dendrobatidis.

eclines are seen in populations affected by Bd and frogs often simply just disapear (Skerratt et al. 2007). Habitat destruction/overexploitation are cited as responsible for the declines of 233 frog species but another 202 frog species are in decline (Stuart et al. 2004). Data likely underestimates the number of animals/species infected with Bd, and Skerett et al. 2007 describes how Bd is likely associated with these declines and not environmental change (Bd is better adapted to cold water and these species are declining in areas where other stressors are not documented).

Figure 2. Distribution of chytrid fungus, Bactrachochytrium dendrobatidis in the Pacific Northwest

Bd was recently detected in the Pacific Northwest infecting multiple species of amphibians (Figure 2, Pearl et al. 2007, Doughton, 2007), and indicated in deaths of both Rana pipiens (=Lithobates) (Doughton, 2007; Figure 3) and R. pretiosa (Pearl et al. 2007, Doughton, 2007) (Figure 4) two species listed as endangered under the Washington state species of concern list ((determined by WAC 232-12-297, section 2.4, WAC 1998). R. pipie ns has a vast geographic distrib ution in North America, and is decline throughout it's range (although considered a species of least concer

Figure 2. Rana pipiens

n by the IUCN Red List of Threatened Species (IUCN 2008) )(McAllister, 1999, IUCN 2008a) and at present R. pipiens has only been confirmed contained in two areas of the Crab Creek drainage in Grant Count, Washington State (McAllister et al., 1999). R. pretiosa is contained in the Pacific Northwest with a range from southern British Columbia to Northern California, and is in decline and listed as

Figure 3. R. pretiosa.

vunerable by IUCN (2008b); in Washington state, R. pretiosa is only currently known to inhabitat three areas. Both species are endangered ((determined by WAC 232-12-297, section 2.4, WAC 1998), and have seen severe declines in Washington state (McAllister and Leonard, 1999, McAllister et al. 1999).
Bd was first described in 1998 (Berger 1998), but has been identified as early as 1938 in museum specimens of Xenopas lavevis , the African clawed frog (Weldon et al. 2004), and likely originated in the African clawed frog (Xenopas lavevis) based on known data (reviewed by Skerratt et al. 2007). The African clawed frog and other amphibian species have been transported through global amphibian trade likely leading to the global spread of Bd (Fisher and Garner 2007). Currently, groups are lobbying for increased regulation of the amphibian trade to stop the spread of Bd (Fisher and Garner 2007). Bd has low genetic variability with most variation found in Africa (Moorhouse et al. 2003), however genotypic, phenotypic, and proteotypic isolates exist and are likely linked to pathogen virulence (Fisher et al. 2009).

In adult amphibians, Bd initially colonizes the skin with water born zoospores where it replicates within epithelial cells and transforms into a thallus and later a zoosporangium (which then releases zoospores) (reviewed by Rollins-Smith and Conlon 2005). Virulence factors of Bd are not known but it may produce a 1) toxin or 2) interfere with the fluid and ion balances of the skin (reviewed by Rollins-Smith and Conlon 2005). Antimicrobial peptides produced in granular glands of the skin of some species of frogs can inhibitat growth and provide protection for some species against the pathogen (Rollins-Smith and Conlon 2005). Not all species are affected by Bd as described in the laboratory and the field, and microbial peptide activity (based on in vitro ability) is greater in species with lower susceptibility to Bd (Woodhams et al. 2006), and survival in laboratory experiments has been correlated with increased effectiveness of these peptides (Woodams et al. 2007). Adaptive immunity to Bd has not been described in the literature, and this may also play a role in host defense against Bd (Woodhams et al. 2007).

The data presented in the papers by Woodhams et al. 2006, 2007 are important first steps in understanding how antimicrobial defenses affect survival but are based on a limited number of animals (not representative of the species range) (Woodhams et al. 2006), one family per species (Woodham et al. 2007), and the use of non-declining frog species (Kurtz and Scharasack 2007). Additionally, Kurtz and Scharsack (2007) provide commentary to Woodhams and colleagues work expressing interest in further study of antimicrobial peptides in 1) the wild environment, 2) additional species (particularly those in decline) and 3) more individuals within a species (i.e. bred family groups). Adaptive immunity may also play a role in host defense against Bd and may act with antimicrobial peptides (Woodhams et al. 2007, Kurtz and Scharsack 2007). One species that showed increased peptide activity against Bd is Rana pipiens and this species has been described as "less susceptible" (Woodhams et al. 2006). However, given the expansive range of R. pipiens it is unlikely that every population of this species is able to effectively mount a defense against the pathogen particularly in an area such as Washington state where the population is endangered. Additionally, given that very little regulation is currently in place against Bd on the local, national or global level this problem is likely to spread to other endangered populations. Only time will tell whether R. pipiens and R. pretiosa will survive the impacts of Bd to maintain populations in the state of Washington or whether these species will become exitinct in the state of Washington. Will they simply disapear like many frog species?

Web links
IUCN Red List of Endangered Species
Histological diagnosis of //Batrachochytrium dendrobatidis//
Amphibian Ark
Amphibian Ark--Chytrid fungus and chytridio mycosis
msnbc.com article on Amphibian Ark
James Cook University Amphibian Disease Home Page
Seattle times article on state frog captive breeding program

References

Berger, L., Speare, R, Daszak, P, Green, D.E., Cunningham, A.A., Goggin, C.L. et al. 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 of the United States of America 95: 1031-9046.

Doughton, S. 2008. Fungus threatens state’s frogs, salamanders. The Seattle Times available at: http://seattletimes.nwsource.com/html/localnews/2004387294_sickfrogs02m.html Accessed on 15 March 2009
Fisher, M.C. and T.W.J. Garner. 2007. The relationship between the emergence of Batrachochytrium dendrobatidis, the international trade in amphibians and introduced amphibian species. Fungal Biology Reviews. 21: 2-9.
Fisher, M.C., Bosch, J., Yin, Z., Stead, D.A., Walker, J., Selway, L., Brown, A.J.P., Walker, L.A., Gow, N.A., Stajichs, J.E., and Garner, T.W.J. 2009. Proteomic and phenotypic profiling of the amphibian pathogen Batrachochytrium dendrobatidis shows that genotype is linked to virulence. Molecular Ecology 18: 415-429.
IUCN 2008a. Lithobates pipiens. Information obtained 15 March 2009 at http://www.iucnredlist.org/details/58695
IUCN 2008b. Rana pretiosa. Information obtained 15 March 2009 at http://www.iucnredlist.org/details/19179
Kurtz, J. and J.P. Scharasack. 2007. Resistance is skin-deep: innate immunity may help amphibians to survive a deadly fungus. Animal Conservation 10: 422-424.
Morehouse, E.A., James, T.Y., and Ganley, A.R.D. 2003. Multilocus sequence typing suggests the chytrid pathogen of amphibians is a recently emerged clone. Molecular Ecology 12: 395-403.
McAllister, K. R. and W. P. Leonard. 1997. Washington State status report for the Oregon Spotted Frog. Wash. Dept. Fish and Wildl., Olympia. 38 pp.
McAllister, K.R., Leonard, W.P., D.W. Hays, and R. C. Friesz. 1999. Washington state status
report for the northern leopard frog. Wash. Dept. Fish and Wildl., Olympia. 36 pp.
Pearl, C.A., Bull, E.L, Green, D.E., Bowerman, J., Adams, M.J., Hyatt, A., and Wente, W.H. 2007. Occurrence of the amphibian pathogen Batrachochytrium dendrobatidis in the Pacific Northwest. Journal of Herpetology 41(1) 145-149
Rollins-Smith, L.A. and J.M. Conlon. 2005. Antimicrobial peptide defenses against chytridiomycosis, an emerging infectious disease of amphibian populations. Developmental and Comparative Immunology 29: 589-598.
Skerratt, L.F., Berger, L., Speare, R., Cashins, S., McDonald, K.R., Phillott, A.D., Hines, H.B., and N. Kenyon. 2007. Spread of chytridiomycosis has caused the rapid global decline and extinction of frogs. Ecohealth 4: 125-134.
Stuart, S.N., Chanson, J.S., Cox, N.A., Young, B.E., Rodrigues A.S.L., Fisherman D.L., et al. 2004. Status and trends of amphibian declines and extinctions worldwide. Science 306: 1783-1786.
WAC 1998.WAC 232-12-297 Endangered, threatened, and sensitive wildlife species classification . Information obtained 15 March 2009 at http://www.wdfw.wa.gov/wlm/diversty/soc/wac-297.htm
WDFW 2008. Washington Department of Fish and Wildlife State Species of Concern, State Endangered Species. Obtained 15 March 2009 at http://www.wdfw.wa.gov/wlm/diversty/soc/endanger.htm
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(12): 2100-2104.
Woodhams, D.C., Voyles, J., Lips, K.R., Carey, C., and Rollins-Smith, L.A. 2006. Predicted disease susceptibility in a Panamanian amphibian assemblage based on skin peptide defenses. Journal of Wildlife Diseases 42: 207-218.
Woodhams, D.C., Ardipradja, K., Alford, R.A., Marantelli, G., Reinert, L.K., and Rollins-Smith-L.A. 2007. Animal Conservation 10 409-417.