Case notes on adverse reactions associated with ivermectin therapy of Atlantic salmon

This paper presents data collected during routine investigations of seven cases of morbidity and mortality that occurred in farmed Atlantic salmon receiving oral ivermectin therapy. The investigations did not include collection of a full range of clinically relevant data. There appeared, however, to be an association between toxic reactions and treatments at lower water temperatures. Histological analysis revealed no characteristic lesions in the moribund fish examined. Median ivermectin concentrations in the muscle, liver and brains of moribund fish were 133 μg/kg, 416 μg/kg and 177 μg/kg, respectively. In fish that remained apparently healthy after therapy the concentrations in the same tissues were 43 μg/kg, 57 and 46 μg/kg. An attempt is made to indicate the possible significance of these data for diagnostic studies and for considerations of human health issues.