Pilot study demonstrating that immunostimulation with β glucan fails to moderate the immunosuppressive effects of dexamethasone when co-administered to rainbow trout Oncorhynchus mykiss experimentally challenged with the microsporidian Loma salmonae

In this pilot study, juvenile rainbow trout were experimentally challenged with the microsporidian Loma salmonae to determine the effects of immunostimulation with β-1,3/1,6 glucan administered in the feed at 200 mg/kg of feed, and immunosuppression with dexamethasone at 300 mg/kg of feed when these were administered in the early stages of infection. Six weeks after oral exposure to Loma spores, control fish developed a mean of 34.8 spore filled xenomas per gill arch; those which had received β glucan had significantly fewer xenomas (23.6) whereas those receiving dexamethasone had significantly more (43.0). Paradoxically, when fish received both β glucan and dexamethasone in any of three temporal combinations, xenoma numbers were significantly higher (51.0-65.1) even when compared to fish receiving only dexamethasone.