Meta-analysis showing that immunisation is an effective method to reduce amphibian susceptibility to the chytrid fungus

Meng-Han Chung, Richard P Duncan, Daniel W.A. Noble, Benjamin Scheele, Simon Clulow

Emerging infectious diseases are increasingly causing mortality in vertebrates, driving widespread population declines in some species. Amphibian chytridiomycosis is a lethal fungal disease that has caused population collapses and extinctions worldwide. Identifying approaches that can effectively enhance host survival is therefore an urgent conservation priority. Here, we investigate whether immunising individuals against chytrid is an effective strategy. We synthesised evidence from 223 effect sizes (53 experiments across 36 studies and 22 species) to evaluate how susceptibility to Batrachochytrium dendrobatidis (infection rates, infection intensity, mortality) differed between experimentally immunised and non-immunised individuals that were subsequently exposed to live chytrid. Individuals immunised by exposure to live chytrid, their cell-free compounds, or synthetic antiparasitics consistently had reduced disease susceptibility follow re-exposure, although effectiveness varied across the stages of disease progression, depended on life stage, and varied among taxonomic groups. In contrast, we found no clear benefits of probiotic or dead-pathogen immunisation. These findings highlight three promising immunisation methods that reduce amphibian susceptibility to the chytrid fungus. They also suggest that wild animals exposed to chytrid may benefit from habitat manipulations, such as providing thermal refugia or targeted chemical disinfection, that enable animals to clear infection, thereby inducing live-pathogen immunity that could enhance survival in susceptible species.