Relationship between two pathogens in an amphibian community that experienced mass mortalities.

As host species tend to harbor multiple parasite species, co-infection within a host is a common rule in nature. The chytrid fungus Batrachochytrium dendrobatidis (Bd) and the viruses in the genus Ranavirus (Rv) are emerging pathogens responsible for the decline of amphibians worldwide. Despite their common geographical co-occurrence and the serious conservation issue that co-infection with these pathogens could represent, little is known about their possible synergistic interactions and effects within a host community. Here, we investigated the occurrence and associations between these two pathogens within an amphibian community after Rv-driven disease outbreaks detected in four populations of the Iberian ribbed newt (Pleurodeles waltl) in North-Western Spain. Just a few months after the last mass mortality event, Rv infection parameters at the affected sites significantly decreased, or were even lower than such registered at the sites where no outbreaks were reordered. Both pathogens, Bd and Rv, were simultaneously present in almost all sites, but co-infection within a single host was rarely detected. Our findings suggest that the co-occurrence of both pathogens does not predict adverse outcomes following an outbreak, such as enhanced susceptibility of hosts to one pathogen due to the presence or infection intensity of the other. Indeed, we found that other variables (as species identity or site) were more important than infection with a pathogen in predicting the infection status and severity with the other. This study highlights the importance of host-specific and environmental characteristics in the dynamic of both infections, co-infection patterns and their impacts. This article is protected by copyright. All rights reserved.