The potential
antiparasitic and immunomodulatory effect of three treatments against myxosporean parasites on the innate immune system of sharpsnout sea bream (Diplodus puntazzo) was investigated. Fish naturally infected with Myxobolus sp. (Bivalvulida/Platysporina), a histozoic parasite mainly affecting the renal interstitial tissue, were treated by
oral administration of a combination of
salinomycin with
amprolium, Origanum
essential oil or
fumagillin in a small-scale field trial. Various leucocyte functions influenced by myxosporean
infection were examined in order to determine treatment effects on leucocyte immunocompetence of treated fish. One month post treatment all drugs caused a significant decrease in prevalence and intensity of
infection in comparison to untreated, infected fish. The effect was most prominent in
salinomycin with
amprolium treated fish, which 1-month post treatment contained either no
cysts at all or a few spores free in melanomacrophage centres revealing almost total elimination of the parasite and the
antiparasitic action of the treatment. There was no histopathological evidence of
drug toxicity.
Antiparasitic action was accompanied by a significant enhancement of phagocytic activity demonstrated by ingestion of large numbers of
latex beads and the secretion of high levels of reactive
nitrogen intermediates by phagocytes in vitro. Complete restoration of the diminished mitogenic responses and serum
lysozyme secretion was also detected in
salinomycin with
amprolium-treated fish compared to untreated, infected fish. These data suggest that salilomycin with
amprolium may be a promising treatment for myxosporean
infections in intensively cultured warm-water fish, exhibiting action partially via the enhancement of host, innate immune functions and leading to parasite elimination.