Cortisol influences the hostparasite interaction between the rainbow trout (Oncorhynchus mykiss) and the crustacean ectoparasite Argulus japonicus

Abstract

The host-parasite interaction between the rainbow trout Oncorhynchus mykiss and the fish louse Argulus japonicus was investigated by administering low levels of dietary cortisol before infecting the fish with low numbers of the parasite. After 24 h, the dietary cortisol treatment elevated blood cortisol and glucose levels and stimulated the synthesis of secretory granules in the upper layer of skin cells. Infection with 6 lice per fish caused skin infiltration by lymphocytes, also in areas without parasites. The lymphocyte numbers in the blood at 48 h post-parasite infection were reduced. Other changes, typical for exposure to many stressors and mediated by cortisol, were also found in the epidermis of parasitized fish, although neither plasma cortisol nor glucose levels were noticeably affected. Glucocorticoid receptors were localized immunohistochemically and found in the upper epidermal layer of pavement and filament cells, and in the leucocytes migrating in these layers. Cortisol-fed fish had reduced numbers of parasites and the changes in the host skin are likely involved in this reduction. Thus a mild cortisol stress response might be adaptive in rejecting these parasites. Further, the data suggest that this effect of cortisol is mediated by the glucocorticoid receptor in the skin epidermis, as these are located directly at the site of parasite attachment and feeding in the upper skin cells that produce more secretory granules in response to cortisol feeding.

The effects of Lepeophtheirus salmonis infections on the stress response and immunological status of Atlantic salmon (Salmo salar)

“…Positive correlations have previously been found between cortisol and lysozyme in Atlantic salmon and rainbow trout [21]. Small increases in cortisol, as seen in uninfected fish, can have an immunostimulatory effect [30]. As TGFb is a potent inhibitor of cytotoxic T lymphocyte activation, which involves MH class I molecule presentation, a negative correlation between the levels of these two genes is not unexpected [39].…”

Host tolerance and resistance to parasitic nest flies differs between two wild bird species

“…Outside of resource provisioning, blood glucose levels and subsequent glucocorticoids can also be a sign of stress. Studies have found evidence connecting parasite load to glucocorticoid and stress levels (Haond, Nolan, Ruane, Rotllant, & Wendelaar Bonga, 2003;Raouf, Smith, Brown, Wingfield, & Brown, 2006). Glucocorticoids can also regulate immune function as certain concentrations can either enhance or inhibit certain immune functions, such as immunity or inflammation (Cain & Cidlowski, 2017).…”

Evidence of ectoparasite-induced endocrine disruption in an imperiled giant salamander, the eastern hellbender (Cryptobranchus alleganiensis)

“…Corticosterone inhibition in hellbenders could be beneficial for the leeches. For instance, fish with lower plasma cortisol concentrations had higher copepod infections, likely due to suppression of cortisol-stimulated changes in the skin that can help to prevent parasite infection (Haond et al, 2003). Additionally, there is some evidence that parasites can manipulate host hormones to increase their success by reducing host immune responses, or by directly utilizing host hormones for growth and reproduction (Escobedo et al, 2005).…”