Robbie Richards, a PhD student at the Odum School of Ecology, studies the gastrointestinal worm parasites of wild ungulates on the National Bison Range in Montana. Richards got his start studying Trichostrongylus axei, a gastrointestinal worm found commonly in bison. Now he wants to understand the ecology of the whole suite of worms infecting the entire ungulate community.
Richards’s data, generated through molecular barcoding, answer questions about which species are the most important to the transmission of “multi-host” parasites, or parasites that have the ability to infect more than one host species. The data set emerged from previous work conducted by Dr. Vanessa Ezenwa, a professor at the Odum School of Ecology, whose research integrates field and laboratory approaches to understanding host-parasite interactions in wild populations. Richards is using these data to ask new questions. Which host species — ranging from bison to bighorn sheep and pronghorn antelope — play the most important role in spreading each species of worm. Particularly, are there any species that serve as “super-spreaders” in this widely ranging ecological community? To answer these questions, Ezenwa and Richards first evaluated how traits of individual species, like their abundance or the degree to which they excrete worm eggs, influence their role in parasite transmission. Results so far suggest that species are not characterized by any typical level of parasite shedding, but rather exhibit a tremendous amount of variation among individuals. Further, the number of individuals of each species on the range also proved to be very important.
To better account for these many factors, Richards consulted Dr. John Drake, another professor at the Odum School, who specializes in developing computer models of such complex systems. Richards and Drake are now developing a spatial model to understand how infection risk varies across the range and which species are most responsible for transmission at different locations. This new model will consider variation in the abundance of each species across the different habitat types present in an effort to locate “hot spots” in transmission and the species responsible.
What this work shows is how collaboration can lead to scientific innovation. Richards has found that answering his questions about how different host species contribute to transmission, including identifying those species that are super-spreaders, has been greatly aided by the use of models to synthesize theory and data. This work has inspired Richards’s evolving interest in the complexities of multi-host, multi-parasite systems and hints at approaches that may make such complicated systems newly tractable. Making the most out of Odum’s multifaceted pedagogical approach toward emerging problems in infectious disease, Richards’s research should be of interest to both infectious researchers and wildlife managers interested in understanding, predicting and controlling the spread of parasites in real-world host communities.