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Diseases of Aquatic Organisms

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DAO 68:51-63 (2005)  -  doi:10.3354/dao068051

Life cycle stages of the amphibian chytrid Batrachochytrium dendrobatidis

Lee Berger1,2,*, Alex D. Hyatt2, Rick Speare1, Joyce E. Longcore3

1Amphibian Disease Ecology Group, School of Public Health, Tropical Medicine and Rehabilitation Science, James Cook University, Townsville, Queensland 4811, Australia
2Australian Animal Health Laboratory, CSIRO Livestock Industries, Private Bag 24, Geelong, Victoria 3220, Australia
3Department of Biological Sciences, University of Maine, Orono, Maine 04469-5722, USA

ABSTRACT: An overview of the morphology and life cycle of Batrachochytrium dendrobatidis, the cause of chytridiomycosis of amphibians, is presented. We used a range of methods to examine stages of the life cycle in culture and in frog skin, and to assess ultrastructural pathology in the skin of 2 frogs. Methods included light microscopy, transmission electron microscopy with conventional methods as well as high pressure freezing and freeze substitution, and scanning electron microscopy with critical point drying as well as examination of bulk-frozen and freeze-fractured material. Although chytridiomycosis is an emerging disease, B. dendrobatidis has adaptations that suggest it has long been evolved to live within cells in the dynamic tissue of the stratified epidermis. Sporangia developed at a rate that coincided with the maturation of the cell, and fungal discharge tubes usually opened onto the distal surface of epidermal cells of the stratum corneum. A zone of condensed, fibrillar, host cytoplasm surrounded some sporangia. Hyperkeratosis may be due to (1) a hyperplastic response that leads to an increased turnover of epidermal cells, and (2) premature keratinization and death of infected cells.

KEY WORDS: Batrachochytrium dendrobatidis · Chytridiomycosis · Fungus · Morphology · Ultrastructure · Transmission and scanning electron microscopy · Pathology · Amphibian

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