Lesions of experimental flea bite hypersensitivity in the dog.

Hypersensitivity to fleas was induced in flea-naive dogs by controlled challenge exposure to virgin fleas. By week 10 of the investigation, immediate (15 minute) and delayed (24-48 hours) responses could be elicited in the skin by flea bites. Histologically, the immediate response consisted of edema and eosinophils which sometimes overlapped with a delayed inflammatory response comprised of perivascular lymphocytes and fewer histiocytes. These inflammatory patterns correlated with type I or immediate, and type IV or cellular, allergic reactions. The combined immediate and delayed responses to fleas in the dog are as observed by other investigators in man and guinea pigs.