Circulating antibodies and blood histamine in cattle after treatment against hypodermosis

Studies have been made of the effect of treatment with an organophosphorus insecticide on calves with or without Hypoderma infestation. A close relationship has been demonstrated between variations of circulating antibodies and blood histamine levels. It is suggested that histamine is released following an immunological reaction due to the formation of complexes between antigenic proteins of the dying larvae and circulating antibodies. Other etiologic agents such as intrinsic larval toxicity were also examined. The small variations of histamine levels suggest that histamine plays only a minor part in the mediation of symptoms of anaphylaxis often observed in parasitised cattle after preventive treatment against hypodermosis.