Specific immunotherapy in the treatment of Culicoides hypersensitive horses: a double-blind study.

Fourteen privately owned horses completed a six month, controlled, double-blind trial to assess the efficacy of immunotherapy using an aqueous extract of whole, unfed Culicoides variipennis in the treatment of Culicoides hypersensitivity. Selected horses had a history of a seasonal, pruritic dermatitis, clinical signs and distribution compatible with Culicoides hypersensitivity, failed to improve in response to ivermectin therapy, and reacted to several dilutions of Culicoides extracts without significant reactivity to other possible allergens including insects, moulds and feeds. One horse from the control group (n = 8) and one from the test group (n = 6) improved. Statistically, there was no significant difference between horses on Culicoides antigen and control horses. In each group, four owners thought that their horses had improved.