I use theory from evolutionary epidemiology to gain a better understanding of how hosts (including us humans) use macronutrients and calorie restriction during infection: defense strategy or parasite manipulation?
Photo credit: J. Rosen
Food for thieves: Mind control, resource wars, & virulence evolution
You may have heard the old adage 'feed a cold and starve a fever' ? Or you may be familiar with your own decrease in appetite or certain cravings that accompany certain illnesses? Well, it turns out that these temporary, but substantial shifts in appetite during illness (aka ‘pathogen-mediated anorexia’) is a rather ubiquitous behavior in hosts ranging from flies to humans.
Numerous studies have documented this so-called ‘sickness behavior’ and it’s association with the acute-phase response of the innate immune system. Yet, we still do not understand whether this behavior benefits the host, pathogen/parasite, both, or neither.
Perhaps more importantly, we do not understand the high-order consequences of altering this behavior. Nonetheless, many common biomedical and veterinary practices alter both the magnitude and duration of the anorexic symptom.
For example, the ubiquity of this behavior, combined with mounting evidence that calorie restriction can improve host health, emphasizes the importance of harnessing host nutrition as a non-pharmacological strategy to combat disease.
However, these efforts overlook that within-host resources also fuel parasite traits (e.g., virulence and transmission), consequently affecting disease severity and prevalence.
Our research takes an integrative approach to understanding this ubiquitous but poorly understood component of host-pathogen interactions.
Using an adaptive dynamics approach, we show that reducing within-host nutrients (via parasite-mediated anorexia or prescribed calorie restriction) can either enhance or diminish disease severity, depending on whether the host’s diet bolsters or suppresses immune function and parasite production. Subsequently, depending on dietary context, interventions that suppress anorexia (overfeed) could backfire, inadvertently selecting for more virulent parasites and larger epidemics.
A central focus of my research program is testing these predictions using detailed experiments in Daphnia, Drosophila, and longitudinal data from livestock studies.
Using adaptive dynamics and a co-evolutionary framework, we illustrate how changes in resource acquisition (e.g., via anorexia or calorie restriction) can alter the size and severity (virulence) of epidemics. Outcomes depends on how changes in resources affects mechanisms of resistance, tolerance, or parasite coercion. See Hite et al., in press @ TREE
Associated Publications
1. Hite J.L., A. Pfenning, and C.E. Cressler. 2020 Starving the Enemy? Feeding behavior shapes host-parasite interactions. Trends in Ecology and Evolution.
2. Hite J.L. and C.E. Cressler. 2020. Parasite-mediated anorexia, dietary context, and the evolution of virulence. Integrated and Comparative Biology.