Characterizing the hydrological spread of prion diseases through interdisciplinary science
Chronic wasting disease (CWD) is a 100% fatal disease found in cervids, which include deer, elk, and moose. CWD has been spreading more rapidly across Minnesota and much of North America in the past few years, causing people to come into contact with the disease more frequently through hunting, hide tanning, and consuming contaminated venison. This has raised concerns from epidemiologists that CWD, which has no cure, could evolve to infect humans sooner rather than later. Worries about CWD exposure and spread go beyond wildlife because the pathogens that cause CWD, called infectious prions, can contaminate the environment. Infectious prions are misfolded proteins with a highly stable structure, making them more difficult to degrade than viruses or bacteria. Their unique structure allows them to remain infectious for years in environmental materials, including soil and water. This means that areas with CWD outbreaks could remain an infection risk long after infected animals have been removed. Prions can also be carried by water, and if they reach a stream or river, they can travel over greater distances than deer, further spreading the disease across the landscape. In order to contain the disease and prevent it from infecting humans, we must understand how it moves through the environment.
Exploring this unique intersection of wildlife disease and environmental science requires an interdisciplinary approach. That’s why researchers from multiple fields came together several years ago to establish the Minnesota Center for Prion Research and Outreach (MNPRO), a group devoted to studying prion diseases in order to protect human, wildlife, environmental, and cultural health. Since 2022, I have collaborated with fellow MNPRO scientists to determine how, how far, and how quickly infectious prions are traveling through rivers, streams, and watersheds in Minnesota.
Researching hydrological prion movement is challenging because they are too dangerous to add to the environment for direct observation, and there is no good proxy to replicate their dynamics. There is little prior research about how these mysterious pathogens travel in the environment, so we developed creative methods to predict their movement without traditional experimental methods. One key finding laid the groundwork for our ongoing research: infectious prions preferentially attach to fine particles in surface waters. This means that prions are likely carried by sediments in rivers and streams, rather than free-floating in the water. Thus, in order to predict the how far and how quickly prions are moving through a watershed, we can focus on characterizing sediment movement.
This summer, I have been conducting sediment transport experiments in a flume at the St. Anthony Falls Laboratory. I packed the
flume with sediment mixtures of different median particle sizes to represent diverse streambeds in Minnesota. Then, I adjusted the water flow rate, water depth, and slope of the flume until sediment particles on the bed began to move. The conditions which initiate sediment motion are called critical conditions; the stress exerted on the streambed must be greater than or equal to critical stress in order for sediments to move. I am comparing these critical flow measurements to streamflow data recorded in CWD-contaminated watersheds in order to determine how often sediments are mobile in contaminated streams, and thus how often prions are mobile. With these estimates, we can predict how far prions may have been transported from contaminated sites and how quickly they will reach downstream locations.
This method allows us to estimate prion transport without directly tracing them in streams. Hydrological transport predictions will aid in better assessing risk to the public downstream of detected CWD cases, guiding further CWD testing in previously unmonitored areas, and developing more comprehensive containment strategies to protect human and environmental health.