Meta-analysis identifies effective immunisation approaches to reduce susceptibility to a deadly amphibian fungus

Infectious diseases cause morbidity and mortality in vertebrates, driving widespread population declines. More than 500 amphibian species are currently threatened by chytridiomycosis, a lethal fungal disease that has caused population collapses and extinctions worldwide. Identifying approaches that can effectively enhance host resistance 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 infection rates, pathogen loads, and 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 enhance amphibian resistance 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.