Enzootic and epizootic dynamics of the chytrid fungal pathogen of amphibians.
Chytridiomycosis, the disease caused by the chytrid fungus, Batrachochytrium dendrobatidis (Bd), has contributed to amphibian population declines and extinctions worldwide. The impact of this pathogen, however, varies markedly among amphibian species and populations. Following invasion into some areas of California's Sierra Nevada, Bd leads to rapid declines and local extinctions of frog populations (Rana muscosa, R. sierrae). In other areas, infected populations of the same frog species have declined but persisted at low host densities for many years. We present results of a 5-year study showing that infected adult frogs in persistent populations have low fungal loads, are surviving between years, and frequently lose and regain the infection. Here we put forward the hypothesis that fungal load dynamics can explain the different population-level outcomes of Bd observed in different areas of the Sierra Nevada and possibly throughout the world. We develop a model that incorporates the biological details of the Bd-host interaction. Importantly, model results suggest that host persistence versus extinction does not require differences in host susceptibility, pathogen virulence, or environmental conditions, and may be just epidemic and endemic population dynamics of the same host-pathogen system. The different disease outcomes seen in natural populations may result solely from density-dependent host-pathogen dynamics. The model also shows that persistence of Bd is enhanced by the long-lived tadpole stage that characterize these two frog species, and by nonhost Bd reservoirs.
Briggs
Cheryl J
CJ
Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106, USA. briggs@lifesci.ucsb.edu
Knapp
Roland A
RA
Vredenburg
Vance T
VT
D000818:Animals; D002140:California / Q000453:epidemiology; D008411:Chytridiomycota / Q000472:pathogenicity* / Q000502:physiology; D054884:Host-Pathogen Interactions; D008954:Models, Biological; D009181:Mycoses / Q000453:epidemiology* / Q000382:microbiology; D011157:Population Dynamics; D011898:Ranidae / Q000382:microbiology*; D014774:Virulence
Science. 2009 Oct 23;326(5952):582-5
19900897
Nature. 2007 May 31;447(7144):E4-5; discussion E5-6
17538572
Dis Aquat Organ. 2005 Dec 30;68(1):65-70
16465835
Aust Vet J. 2004 Jul;82(7):434-9
15354853
Dis Aquat Organ. 2007 Aug 13;77(1):1-9
17933392
Dis Aquat Organ. 2007 Jan 18;73(3):175-92
17330737
Dis Aquat Organ. 2004 Aug 9;60(2):141-8
15460858
Proc Natl Acad Sci U S A. 1998 Jul 21;95(15):9031-6
9671799
PLoS One. 2009 Dec 22;4(12):e8408
20027316
Ecology. 2008 Jun;89(6):1627-39
18589527
Dis Aquat Organ. 2004 Oct 21;61(1-2):75-83
15584413
Conserv Biol. 2009 Oct;23(5):1242-52
19774709
Dis Aquat Organ. 2007 Dec 13;78(2):87-95
18286805
Emerg Infect Dis. 2004 Dec;10(12):2100-5
15663845
PLoS Biol. 2004 Nov;2(11):e351
15502873
Nature. 2006 Jan 12;439(7073):161-7
16407945
Proc Biol Sci. 2010 Feb 22;277(1681):519-28
19864287
Mycologia. 2004 Jan-Feb;96(1):9-15
21148822
PLoS One. 2009 Aug 04;4(8):e6494
19701481
Proc Biol Sci. 2008 Feb 7;275(1632):329-34
18048287
Proc Natl Acad Sci U S A. 2006 Feb 28;103(9):3165-70
16481617
Proc Natl Acad Sci U S A. 2010 May 25;107(21):9689-94
20457913
Ecology. 2006 Jul;87(7):1671-83
16922318
Dis Aquat Organ. 2005 Dec 30;68(1):51-63
16465834