New Paper Led by Bard Biology Professor Felicia Keesing Calls for More Rigorous Study of Dilution Effects in Natural Ecosystems to Better Understand the Ecology of Infectious Diseases

The COVID-19 pandemic has highlighted the global importance—and challenge—of understanding the ecology of infectious diseases, especially in regard to the impact biodiversity has on the transmission of zoonotic diseases. A new paper in Ecology Letters coauthored by Bard Biology Professor Felicia Keesing and Rick Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies, argues that one key to improving this understanding is more rigorous and creative study of dilution effects, which occur when the diversity of an ecological community reduces the transmission of disease. Dilution effects have been used for decades to manage the transmission of parasites and pathogens in plants, animals, and people.

“The impacts of diversity on the emergence and transmission of pathogens have never been more relevant,” write Keesing and Ostfeld in their paper, “Dilution effects in disease ecology.” “Over the last 20 years, attention has focused on whether the patterns that can be made to happen—when someone chooses which organisms are present in a system—ever happen naturally, as diversity changes under natural conditions, This is a particularly important question because diversity within natural ecosystems is changing rapidly in response to human impacts such as habitat fragmentation, overexploitation, pollution and climate change.”

In their paper, Keesing and Ostfeld discuss how and where dilution effects have been used to manage infectious diseases. “We explore the ecological mechanisms that underlie these effects, and then turn to more recent questions—whether dilution effects occur in natural communities, and if so, whether these effects are impacted by changes to natural biodiversity,” they write. “We review the evidence for when and how frequently natural dilution effects occur, outline some of the challenges of studying them and describe common mis-applications of the concepts, as well as important outstanding questions.”

Keesing and Ostfeld write that analyses reveal that natural dilution effects are common, but studying them remains challenging “due to limitations on the ability of researchers to manipulate many disease systems experimentally, difficulties of acquiring data on host quality and confusion about what should and should not be considered a dilution effect.” Important questions for future research, they write, include: “Does the pattern of variation in host quality vary in predictable ways for different metrics (e.g. reservoir competence, vector preference) and across types of disease systems? How do interactions within hosts affect dilution effects in multi-pathogen systems? How common are positive relationships between ecological resilience and host quality? What are the shapes of these relationships when they do occur, and what are their underlying causes? What are the best metrics for measuring transmission across disease systems? What are the characteristics of natural disease systems that show dilution effects and those that do not, and what does this suggest about whether we might apply our understanding of dilution effects to manage diseases in nature?”

Keesing and Ostfeld conclude that there is much to learn about the relationship between biodiversity change and the emergence of pathogens, and that more study of dilution effects will be essential. “Important questions include how biodiversity, and its loss, affect the emergence of pathogens of non-human hosts; how we can effectively determine whether hosts can actually transmit pathogens, as opposed to simply becoming infected with them and how to manage our behavior and use of landscapes to minimize spillover events,” they write. “Acknowledging what we have learned about dilution effects in nature over the past 20 years is critically important, as is understanding their similarities and differences to the dilution effects that operate in managed disease systems like agricultural fields.”

To read the full paper in Ecology Letters, click here.

This research was supported by a National Science Foundation Grant OPUS 1948419 to Keesing.

Felicia Keesing, David and Rosalie Rose Distinguished Professor of Science, Mathematics, and Computing, has been on the Bard faculty since 2000. She has a B.S. from Stanford University and a Ph.D. from the University of California, Berkeley. Since 1995, she has studied how African savannas function when the large, charismatic animals like elephants, buffaloes, zebras, and giraffes disappear. She also studies how interactions among species influence the probability that humans will be exposed to infectious diseases. Keesing also studies Lyme disease, another tick-borne disease. She is particularly interested in how species diversity affects disease transmission. More recently, she has focused on science literacy for college students, and she led the re-design of Bard College’s Citizen Science program. Keesing has received research grants from the National Science Foundation, National Geographic Society, National Institutes of Health, Environmental Protection Agency, and Howard Hughes Medical Institute, among others. She has been awarded the United States Presidential Early Career Award for Scientists and Engineers (2000). She is the coeditor of Infectious Disease Ecology: Effects of Ecosystems on Disease and of Disease on Ecosystems (2008) and has contributed to such publications as Nature, Science, Proceedings of the National Academy of Sciences, Ecology Letters, Emerging Infectious Diseases, Proceedings of the Royal Society, Ecology, BioScience, Conservation Biology, and Trends in Ecology & Evolution, among others. (9.8.21)

This event was last updated on 09-10-2021

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