Clinical and histological evaluation of immediate and delayed flea antigenintradermal skin test and flea bite sites in normal and flea-allergic cats

Seven cats diagnosed as flea allergic by specific criteria and seven normal control cats were exposed to flea bites in a controlled manner and were gi ven intradermal injections of 1:1000 w/v flea antigen. Subjective evaluatio n of gross lesions and documentation of histological changes at flea antige n intradermal skin test (IDST) and flea bite sites were performed at 15 min , 24 h and 48 h after IDST or flea exposure. Control cats did not develop a n immediate gross reaction to either flea bites or the intradermal injectio n of flea antigen. All seven flea-allergic cats had an immediate gross reac tion at the site of IDST with flea antigen; five of these cats also develop ed immediate gross reactions to flea bites. Three of seven flea-allergic ca ts developed a gross 24 h and/or 48 h delayed reaction at the flea antigen IDST sites. These three and one other cat had both an immediate and delayed gross reaction to flea bites. Histological examination of 15 min skin spec imens from IDST and flea bite sites of flea-allergic cats were similar with a mild lymphocytic, histiocytic and mastocytic superficial perivascular de rmatitis. Histological examination of 24 h and 48 h skin specimens from IDS T and flea bite sites of flea-allergic cats showed that they were often ind istinguishable. Histological features of IDST and flea bite sites of flea-a llergic cats at 24 h consisted of a perivascular to diffuse predominately e osinophilic dermatitis and mural folliculitis with variable epidermal necro sis and ulceration.