Why must I feel sick? The benefits of sickness behavior in the defense against pathogens

Everyone has experienced sickness behavior during an infection: feeling fatigued, having little appetite, wishing to stay alone, lacking motivation, and maybe even feeling depressed and anxious.

These feelings and behavioral changes occurring during infections are commonly viewed as an irrelevant and unwanted side effect of being infected. But what if sickness behavior constitutes an integrated part of the bodily defenses to face the pathogen threat? In this project, we will, for the first time, test the hypothesis that sickness behavior has an adaptive function.

In two complementary studies, using openly available data from more than 1000 participants who underwent an experimental rhinovirus infection in laboratory settings in one study, and conducting a new highly innovative study using the same model and manipulating sickness behavior during the acute phase of the disease, we will demonstrate that sickness behavior in humans allows supporting the clearance of pathogens.

If the hypotheses prove to be true, this project will provide empirical evidence demonstrating that sickness behavior is a crucial and beneficial part of the defense mechanisms against pathogens, and should be harnessed to promote healing and recovery from infections.

This project will also open up new research directions for testing how harnessing sickness behavior could prevent the development of conditions characterized by maladaptive expression of sickness behavior, such as post-COVID.