The aim of this study is to evaluate the glucocorticoid effect of dexamethasone on acute inflammatory response of tilapia (Oerochromis niloticus), vaccinated and challenged with Aeromonas hydrophila. For that will be used 96 tilapia, weighting about 150g each, distributed in 12 tanks wiht 100 L capacity, supplied with aired water, constituting four treatments: T1 = vaccinated and treated with glucocorticoids, T2 = not vaccinated treated with glucocorticoids, T3 = Non-vaccinated and treated with glucocorticoids; T4 = not vaccinated and not treated with glucocorticoids. It will be evaluated eight animals per treatment in three periods: six, 24 and 48 hours post-challenge (HPD) with A. hydrophila. The vaccination with A. hydrophila bacterin, formalin inactivated, will be held 15 days before the bacterial challenge, after anesthetizing the fish in an aqueous solution of benzocaine (1:500). In the same anesthetic protocol, the challenge will be done by inoculation of 1.0 x 108 CFU of A. hydrophila in the swim bladder, associate to the treatment with the glucocorticoid dexamethasone in groups T1 and T2, at a dose of 2 mg / kg body weight in a 0.2% solution, intramuscular route. Therefore, six, 24 and 48 HPD, tilapia will be submitted to deep anesthesia for blood collection and determination of complete blood count, as well as, perform the dissection of the bladder in order to obtain inflammatory exsudate to determinate the total count of inflammatory cells in Neubauer chamber and differential counts in extension of exsudate stained with May-Grunwald-Giemsa-Wright. However, the correlation between the hematology and cell recruitment in inflammatory exsudates provide important support in understanding and characterization of events that occur in the pathophysiology of acute inflammatory response of tilapia, when previously vaccinated and challenged with A. hydrophila.
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