Impacts of sequential and simultaneous coinfection by major amphibian pathogens on disease outcomes

Abstract In natural environments, hosts frequently experience infections from multiple pathogenic species or strains, significantly influencing disease dynamics. Despite shared susceptible hosts and overlapping distributions, the impacts of coinfections by the two most threatening global amphibian pathogens, Batrachochytrium dendrobatidis (Bd) and Ranavirus (Rv), remain largely understudied. This study offers new insights into how simultaneous and sequential exposures to Bd and Rv influence disease outcomes in an amphibian host under controlled experimental conditions. Our findings reveal that the sequence and timing of pathogen exposure can lead to contrasting outcomes. Animals previously exposed to Rv displayed the highest mortality following Bd infection, whereas simultaneous exposure to both pathogens resulted in higher survival than single infections. These findings suggest that priority effects, driven by differences in the timing and order of pathogen exposure, can exacerbate disease severity in amphibian populations, particularly in communities with persistent, sublethal Rv infections. This study highlights the critical role of pathogen interactions in shaping disease dynamics and emphasizes the importance of integrating coinfections into wildlife disease management strategies to mitigate biodiversity crises in amphibians and beyond.