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Widespread historical presence of Batrachochytrium dendrobatidis in African pipid frogs

Authors

  • Claudio Soto-Azat,

    Corresponding author
    1. Institute of Zoology, Zoological Society of London, Regent’s Park, London NW1 4RY, UK
    2. Escuela de Medicina Veterinaria, Universidad Andres Bello, Republica 252, Santiago, Chile
      Claudio Soto-Azat, Escuela de Medicina Veterinaria, Universidad Andres Bello, Republica 252, Santiago, Chile.
      E-mail: csoto@unab.cl
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  • Barry T. Clarke,

    1. Natural History Museum, Department of Zoology, Cromwell Rd, London SW7 5BD, UK
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  • John C. Poynton,

    1. Natural History Museum, Department of Zoology, Cromwell Rd, London SW7 5BD, UK
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  • Andrew A. Cunningham

    Corresponding author
    1. Institute of Zoology, Zoological Society of London, Regent’s Park, London NW1 4RY, UK
      Claudio Soto-Azat, Escuela de Medicina Veterinaria, Universidad Andres Bello, Republica 252, Santiago, Chile.
      E-mail: csoto@unab.cl
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Claudio Soto-Azat, Escuela de Medicina Veterinaria, Universidad Andres Bello, Republica 252, Santiago, Chile.
E-mail: csoto@unab.cl

Abstract

Aim  Amphibian chytridiomycosis, an emerging infectious disease caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), is associated with global amphibian population declines and species extinctions. Current evidence indicates that the pathogen has recently spread globally from an enzootic focus, with Xenopus spp. (family Pipidae) in South Africa having been identified as a likely source. The aim of this study was to investigate further the likelihood of African Xenopus spp. as the original source of Bd.

Location  We examined 665 museum specimens of 20 species of African and South American pipid frogs collected between 1844 and 1994 and held in the collection of the Natural History Museum, London.

Methods  Skin brushings taken from adult amphibians and brushings from the mouthparts, lips and developing hind limbs of larval pipid frogs were examined for the presence of Bd using real-time PCR.

Results  We found six cases of Bd infection in three Xenopus spp. (from Africa), but none of the South American pipids was positive, although only 45 South American frogs were available for examination. The earliest case of Bd infection was in a specimen of Xenopus fraseri collected from Cameroon in 1933. A consistently low prevalence of infection over time indicates that a historical equilibrium existed between Xenopus spp. and Bd infection in Africa.

Main conclusions  Our results suggest that Bd infection was present in Xenopus spp. across sub-Saharan Africa by the 1930s, providing additional support for the ‘out of Africa’ hypothesis. If this hypothesis is correct, it strengthens the argument for stringent control of human-assisted movements of amphibians and other wildlife world-wide to minimize the likelihood of pathogen introduction and disease emergence that can threaten species globally. Our findings help inform species selection for conservation in the face of the current Bd pandemic and also guide future research directions for selecting Bd isolates for sequencing and virulence testing.

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