Mitchell J. Le Sage, Bailey D. Towey, Jesse L. Brunner
Understanding how infectious diseases are transmitted is crucial to managing their spread and predicting their impacts on at-risk species. One important factor in the transmission of infectious disease is the community in which the pathogen and host exist. This includes any other species, or group of species, that shares a habitat with the infected organism. Scavengers, animals that feed on dead tissue, are functionally well-equipped to influence the spread of disease from the carcasses of infected animals. This is especially true, given that in many disease systems infected carcasses serve as a hub of new infections. There are two ways in which a scavenger could influence the transmission of diseases: 1) by inactivating the pathogen, perhaps by consuming whole carcasses, a scavenger could prevent pathogens from spreading to susceptible individuals, or 2) by not fully consuming, but broadcasting infectious tissue, a scavenger could assist in the spread of pathogens. In either case, broadening our understanding about the importance of the scavenger community in disease ecology gives us tools to make predictions about the success of a pathogen in different communities.
In this study, we directly test the mode of influence that a voracious aquatic invertebrate scavenger (diving beetle larvae of the family Dytiscidae), has on the transmission of a ranavirus from larval Long-toed Salamanders (Ambystoma macrodactylum). Using a series of laboratory experiments, we determined that Dytiscidae larvae are very efficient at consuming larval salamander carcasses, and that the removal of carcasses by the scavenger strongly reduces transmission of Ranavirus from carcasses to live salamander larvae. In addition, there was no evidence that scavenging on infectious carcasses by Dytiscidae larvae releases enough infectious material to increase the number of new infections caused by carcasses. We also carried out a field experiment in which Dytiscidae larvae were exposed to increasing densities of larval salamander carcasses and found that Dytiscidae scavenging alone can remove enough carcass mass to prevent new infections. Our results suggest that in communities with efficient scavengers, scavenging can play an important role to reduce transmission.