Parasite infection leads to widespread glucocorticoid hormone increases in vertebrate hosts: a meta-analysis

1. Parasites and pathogens (hereafter parasites) commonly challenge organisms, but the extent to which their infections are physiologically stressful to hosts remains unclear. Importantly, vertebrate hormones, glucocorticoids (GCs), have been reported to increase, decrease, or show no alterations stemming from infections, challenging the generality of parasite-associated GC responses and motivating a search for important moderator variables. 2. We undertook the first meta-analysis of changes in vertebrate GCs following experimental infection with parasites, extracting 146 effect sizes from 42 studies involving 32 host and 32 parasite species to test for general patterns of GC following infection, as well as the influence of moderators. 3. Overall, infection increased GCs relative to preliminary or control levels when the single largest effect sizes from repeated measures studies were examined, suggesting that parasites of vertebrate hosts can be thought of generally as physiological str...