Most animals, including humans, are infected with multiple parasites simultaneously, but until recently, most infections have primarily been studied in isolation. Emerging evidence from human and wildlife diseases suggests that interactions among parasites co-infecting (i.e., cohabiting) the same host can influence the overall impact on individual host health and disease spread. This research project will examine ways in which co-infecting parasites interact within a host, and investigate the consequences of infection with different combinations of parasites for host health. Free-living (non-parasitic) species often interact directly by competing for food or space, or indirectly via a shared enemy; similarly, communities of co-infecting parasites may compete for limited resources within the host, or attempt to evade host immune defenses triggered by co-occurring parasites. The investigators will use laboratory experiments in mice to manipulate host resources (via nutrition) and parasite community composition (the number and identity of infecting parasites), to test the hypothesis that resource competition and/or predation by the immune system drive changes in interactions between co-infecting parasites with consequences for parasite reproduction, host condition and susceptibility to new parasites. The wealth of immunological and singe-species parasite infection data in laboratory mice provide a strong foundation upon which to build this complex co-infection experiment. Furthermore, the conserved nature of the vertebrate immune system enables broad applicability of study results. Overall, the results of this study will answer fundamental questions about the potential synergistic effects of multiple infections on hosts.

This project will provide research experiences for two undergraduate students in addition to enhancing the doctoral research of a graduate student. The principal investigators will also participate in a program that brings hands-on ecological learning to K-12 classrooms in Georgia. Specifically, methods and results from this project will be used to develop a teaching module on the similarity of ecological processes taking place in the external (e.g. competition and predation between species in free-living communities) and internal environments (e.g. competition and immune evasion between parasites within a single host individual).

Project Report

Most animals, including humans, are infected with multiple parasites simultaneously. Just like all living things, parasites have energy and habitat requirements; they must also avoid predation which to them comes in the form of the host’s immune system. The resources that parasites use and the immune responses they trigger influence how co-occurring parasites interact. The objective of our study was to understand how resources and immune function combine to affect the costs of co-infection for both hosts and parasites. To examine interactions among host resources, immune function, and co-infecting parasites, we conducted a laboratory experiment with mice. Mice were given a high or low quality diet, dosed with two species of helminths (alone and in combination), and then challenged with bovine tuberculosis. Diet strongly influenced host immune function and body condition, as well as parasite survival and reproduction. The magnitude and direction of responses depended on diet quality and the combination of co-infecting parasites. Importantly, we detected an interaction between helminth infection and tuberculosis among mice fed a low protein diet, but not among mice fed a standard high protein diet. Our experiment demonstrates that to understand the real-world consequences of co-infection, studies need to consider the effects of host resources on interactions among different types of parasites. These findings contribute to our general understanding of the significance of co-infection for animal and human health. This project also supported the education of graduate, undergraduate, and K-12 students. Specifically, co-PI and doctoral student Sarah Budischak learned a suite of animal husbandry, immunological, and analytical techniques. Ms. Budischak also developed her teaching skills by mentoring a team of 13 undergraduate students and creating a 7th grade science class lesson related to this project. She led active learning exercises that energized and informed students in 12 middle school classrooms about parasitism, biodiversity, and careers in science. Overall, Ms. Budischak was able to develop as an educator and scientist while mentoring and inspiring over a dozen undergraduate students and over 200 K-12 students.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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Alan James Tessier
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University of Georgia
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