Stress hormones predict a host superspreader phenotype in the West Nile virus system

Abstract

Glucocorticoid stress hormones, such as corticosterone (CORT), have profound effects on the behaviour and physiology of organisms, and thus have the potential to alter host competence and the contributions of individuals to population- and community-level pathogen dynamics. For example, CORT could alter the rate of contacts among hosts, pathogens and vectors through its widespread effects on host metabolism and activity levels. CORT could also affect the intensity and duration of pathogen shedding and risk of host mortality during infection. We experimentally manipulated songbird CORT, asking how CORT affected behavioural and physiological responses to a standardized West Nile virus (WNV) challenge. Although all birds became infected after exposure to the virus, only birds with elevated CORT had viral loads at or above the infectious threshold. Moreover, though the rate of mortality was faster in birds with elevated CORT compared with controls, most hosts with elevated CORT survived past the day of peak infectiousness. CORT concentrations just prior to inoculation with WNV and anti-inflammatory cytokine concentrations following viral exposure were predictive of individual duration of infectiousness and the ability to maintain physical performance during infection (i.e. tolerance), revealing putative biomarkers of competence. Collectively, our results suggest that glucocorticoid stress hormones could directly and indirectly mediate the spread of pathogens.

Bright artificial light at night is associated with increased body mass, poor reproductive success and compromised disease tolerance in Australian budgerigars (Melopsittacus undulatus)

“…In mammals and birds, chronic stress responses represented by quantitative increase in stress hormones, particularly glucocorticoids, can negatively regulate reproductive and immune responses (Nelson & Demas 1996;Verma et al 2017). Elevated corticosterone levels increased viral load in West Nile virus-challenged zebra finches (Taeniopygia guttata) compared with birds with decreased hormonal levels (Gervasi et al 2017). Equally, in corticosterone-treated Adélie penguins (Pygoscelis adeliae), reproductive success decreased by 42% compared with untreated birds (Thierry et al 2013).…”

Viral Diversity of Microbats within the South West Botanical Province of Western Australia

“…Since temporal fluctuation of viral load has been documented in virus surveillance of north American and European microbats [96,97] as well as Hendra shedding in Australian peteropid bats [22,98], longitudinal studies would be required to fully understand the viral shedding and viral-host associations observed here. Furthermore, evidence of higher viral loads as indicators of individual and population scale stress [10] provides a good example of how long-term monitoring of viral prevalence can act as an indicator of environmental pressure on bat communities, particularly with regards to climate change where habitat contracture and distributional shifts may bring together populations harbouring novel viral strains. This approach would allow bat viral research to move beyond prediction of zoonotic disease emergence and be used as a management tool for monitoring the health of cryptic bat communities and the environment as a whole.…”

Extreme Competence: Keystone Hosts of Infections

“…Superattractors and superreceivers are often cast as variants of superspreaders, but their functional roles will depend on covariation between traits affecting (at least) suitability and transmission. In one series of experiments, physiologically stressed, West Nile virus-infected zebra finches (Taeniopygia guttata) attracted twice as many vectors as controls and were infectious to vectors, whereas controls were not [18,19]. There, superattractors were also superspreaders, but in other species low WNV suitability coupled with high vector attractiveness could produce superdiluters.…”

“…One of the best known involves responses to stressors [48]. Variation in stress responses affect multiple aspects of competence in most taxa, but few studies have yet considered whether EC can arise via stress [18,19,49]. Symbionts that live on and within hosts might also affect EC [50], as these organisms sculpt host immune functions and behavior [51,52].…”