Parasite infection leads to widespread glucocorticoid hormone increases in vertebrate hosts: A meta‐analysis

Abstract

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. 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. 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 stressors by elevating GCs. When all effect sizes were included along with the moderator of sampling time post‐infection (tPI), parasite infection still had a positive effect on host GCs. However, the strength of that effect did not relate consistently to tPI, illustrating temporal differences in GC changes during the course of infection among parasite taxa (e.g. arthropod vs. bacterial infections). Other moderator variables examined did not influence GC responses. Studies broadening the range of host and parasite taxa, and sampling during critical time windows, would aid in our understanding of variation in the host stress response and its consequences for fitness of both vertebrate hosts and their parasites.

Salinity stress increases the severity of ranavirus epidemics in amphibian populations

“…Larvae reared in elevated salinity were more likely to die from virus exposure and exhibited suppressed immune function. Previous work also found that ranavirus infection induces a stress response [52] similar to other infections [55]. However, contrary to our expectations for the involvement of the HPI axis, salinity only marginally increased resting glucocorticoid levels.…”

Stress hormone level and the welfare of captive European bison (Bison bonasus): the effects of visitor pressure and the social structure of herds

“…Parasitic infections trigger the host’s immune system, thus activating defensive mechanisms; they are also suspected to affect the release of glucocorticoids. However, the influence of parasites on the host’s glucocorticoid level is still unclear as there are results that suggest both positive and negative correlations, or no relationship at all [ 66 , 67 ]. According to the latest findings, it is advised to correlate fecal glucocorticoid metabolite levels with other factors such as the host’s age, sex and reproductive status, but also parasite type, infestation severity, food availability or social stressors [ 67 ].…”

Physiological condition of Eastern Baltic cod, Gadus morhua, infected with the parasitic nematode Contracaecum osculatum

“…At the level of the individual, parasites can cause adverse effects on the performance capacity of the host ( McElroy and de Buron, 2014 ), e.g. by changing plasma protein and hormone levels ( Akinyi et al , 2019 ; O’Dwyer et al , 2019 ), reducing aerobic and locomotor performances ( Umberger et al ., 2013 ; Hahn et al ., 2018 ) and depleting energy reserves ( Ferrer-Maza et al , 2016 ). Together, this shapes the physiological condition of an infected individual, and impairment may lead to reduced growth and increased mortality ( Marcogliese, 2004 ; Khan, 2005 ; Behrens et al ., 2014 ).…”