Starving the Enemy? Feeding Behavior Shapes Host-Parasite Interactions

The loss of appetite that typically accompanies infection or mere exposure to parasites is traditionally considered a negative byproduct of infection, benefitting neither the host nor the parasite. Numerous medical and veterinary practices directly or indirectly subvert this ‘illness-mediated anorexia’. However, the ecological factors that influence it, its effects on disease outcomes, and why it evolved remain poorly resolved. We explore how hosts use anorexia to defend against infection and how parasites manipulate anorexia to enhance transmission. Then, we use a coevolutionary model to illustrate how shifts in the magnitude of anorexia (e.g., via drugs) affect disease dynamics and virulence evolution. Anorexia could be exploited to improve disease management; we propose an interdisciplinary approach to minimize unintended consequences. Host defense mechanisms fundamentally shape disease dynamics and virulence evolution.Feeding behaviors may play a critical, but overlooked, role in host defense and evolutionary epidemiology.Specifically, hosts typically reduce their feed intake in response to both realized and potential infections, despite the fact that defense mechanisms are energetically costly. The decline in feeding (‘illness-mediated anorexia’) shifts within-host energetics, metabolism, physiology, and immune functions in ways that alter the selective pressures facing parasites.Consequentially, illness-mediated anorexia may drive the evolution of higher or lower virulence, depending on its interactive effects on immunological and parasitological processes.Examining illness-mediated anorexia through the lens of evolutionary epidemiology carries important implications for disease management, especially for livestock and fish.