IMMUNIZATION IS INEFFECTIVE AT PREVENTING INFECTION AND MORTALITY DUE TO THE AMPHIBIAN CHYTRID FUNGUS BATRACHOCHYTRIUM DENDROBATIDIS

The fungal pathogen Batrachochytrium dendrobatidis (Bd), the causative agent of chytridiomycosis, has been implicated in amphibian declines worldwide. It has been hypothesized that low inherent immunogenicity in Bd may be related to the high rates of morbidity and mortality that are associated with Bd-infected anuran populations. To test this idea, juvenile Rana muscosa (mountain yellow-legged frogs) were immunized with adjuvants in combination with a formalin-killed Bd culture to determine if it is possible to stimulate a protective immune response when challenged with a live inoculum of B. dendrobatidis. Three groups of juvenile R. muscosa (6 mo postmetamorphosis) were immunized with saline, Freunds Complete (FCA) and Incomplete Adjuvant (FIA), or the adjuvants in combination with a formalin-killed culture of B. dendrobatidis. The effects of immunization were modeled using survival analysis and a proportional hazards model. No significant differences were found between the groups in overall mortality, time to infection, infection prevalence, or intensity. While this study suggests that immunizing anurans against chytridiomycosis will not alter rates of infection or mortality among individuals, it does raise several questions regarding the attenuation and efficacy of anuran adaptive immune responses and whether they may be protective against this disease.