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The Novel and Endemic Pathogen Hypotheses: Competing Explanations for the Origin of Emerging Infectious Diseases of Wildlife

Authors

  • LARA J. RACHOWICZ,

    Corresponding author
    1. Department of Integrative Biology, 3060 Valley Life Sciences Building, University of California, Berkeley, CA 94720-3140, U.S.A.
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  • JEAN-MARC HERO,

    1. Museum of Vertebrate Zoology, 3101 Valley Life Sciences Building, University of California, Berkeley, CA 94720-3160, U.S.A.
    2. School of Environmental & Applied Sciences, Griffith University Gold Coast, PMB 50 Gold Coast MC, Queensland 4127, Australia
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  • ROSS A. ALFORD,

    1. School of Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia
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  • JOHN W. TAYLOR,

    1. Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, CA 94720-3102, U.S.A.
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  • JESS A.T. MORGAN,

    1. Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, CA 94720-3102, U.S.A.
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  • VANCE T. VREDENBURG,

    1. Department of Integrative Biology, 3060 Valley Life Sciences Building, University of California, Berkeley, CA 94720-3140, U.S.A.
    2. Museum of Vertebrate Zoology, 3101 Valley Life Sciences Building, University of California, Berkeley, CA 94720-3160, U.S.A.
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  • JAMES P. COLLINS,

    1. School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, U.S.A.
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  • CHERYL J. BRIGGS

    1. Department of Integrative Biology, 3060 Valley Life Sciences Building, University of California, Berkeley, CA 94720-3140, U.S.A.
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‡‡Current address: Resources Management and Sciences, Yosemite National Park, 5083 Foresta Road, P.O. Box 700, El Portal, CA 95318, U.S.A., email lara_rachowicz@nps.gov

Abstract

Abstract: Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis, is an emerging infectious disease implicated in declines of amphibian populations around the globe. An emerging infectious disease is one that has recently been discovered; has recently increased in incidence, geography, or host range; or is newly evolved. For any given outbreak of an emerging disease, it is therefore possible to state two hypotheses regarding its origin. The novel pathogen hypothesis states that the disease has recently spread into new geographic areas, whereas the endemic pathogen hypothesis suggests that it has been present in the environment but recently has increased in host range or pathogenicity. Distinguishing between these hypotheses is important, because the conservation measures needed to slow or stop the spread of a novel pathogen are likely to differ from those needed to prevent outbreaks of an endemic pathogen. Population genetics may help discriminate among the possible origins of an emerging disease. Current evidence suggests chytridiomycosis may be a novel pathogen being spread worldwide by carriers; until we know how much genetic variation to expect in an endemic strain, however, we cannot yet conclude that B. dendrobatidis is a novel pathogen.

Abstract

Resumen: La quitridiomicosis, causada por el hongo patógeno Batrachochytrium dendrobatidis, es una enfermedad infecciosa emergente implicada en las declinaciones de poblaciones de anfibios en el mundo. Una enfermedad infecciosa emergente es una que ha sido descubierta recientemente; que ha incrementado en su rango de incidencia, geográfico o de huéspedes recientemente; o que ha evolucionado recientemente. Para cualquier brote de una enfermedad emergente es posible enunciar dos hipótesis en relación con su origen. La hipótesis del patógeno incipiente establece que el la enfermedad se ha extendido recientemente hacia áreas geográficas nuevas, mientras que la hipótesis del patógeno endémico sugiere que ha estado presente en el ambiente pero que ha incrementado en el rango de huéspedes o de patogenicidad. Es importante distinguir entre estas dos hipótesis, porque es probable que las medidas de conservación que se requieren para reducir o detener la dispersión de un patógeno incipiente sean diferentes a las requeridas para prevenir brotes de un patógeno endémico. La genética de poblaciones puede ayudar a distinguir entre los posibles orígenes de una enfermedad emergente. La evidencia actual sugiere que la quitridiomicosis puede ser un patógeno incipiente que esta siendo dispersado por transportistas mundialmente; sin embargo, no podemos concluir que B. dendrobatidis es un patógeno incipiente hasta que no se conozca la variación genética esperada en una cepa endémica.

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