Indirect pathogen transmission underlies an emerging infectious fungal disease outbreak in a wild reptile population

Infectious diseases present a growing risk to wildlife biodiversity. Predicting outbreak dynamics and developing effective management tools require knowledge on the mechanisms of infection transmission. Specifically, understanding the relative contributions of direct host-to-host transmission versus indirect environmental transmission is critical. Here, we leverage a large dataset from long-term monitoring of a free-living population of eastern water dragons (Intellagama lesueurii) experiencing an outbreak of the fungal pathogen Nannizziopsis barbatae to investigate this pathogen's transmission. Using different host behaviours to model direct and indirect transmission of infection in this population, we demonstrate N. barbatae's ability to infect hosts through indirect transmission. Our findings shed light on the danger N. barbatae poses to Australian reptiles but also provide insights into how outbreaks should be managed. Additionally, we provide a methodology to elucidate the transmission mechanisms of driving the spread of emerging fungal pathogens.