Coexistent anaphylaxis to Diptera and Hymenoptera.

Background: Anaphylaxis to the bite of Diptera and specifically the bite of the Tabanidae family (horsefly) have been sparsely documented. The coexistent hypersensitivity to both the order Diptera and Hymenoptera has not been documented.

Methods: We present a patient who experienced anaphylaxis to both insect species. Venom skin testing and RAST revealed sensitivity to several members of the Hymenoptera order. Prick, intradermal and RAST with whole body extracts of Tabanidae species is also documented in this patient. Twenty patients who are sensitive to Hymenoptera and have been bitten by horseflies but have had no reaction to the horsefly bite were used as controls.

Results: An anaphylactic reaction to horsefly bite has been documented in a 56-year-old white male. This patient also demonstrated evidence of anaphylactic reaction to Hymenoptera envenomation. In controls consisting of 20 patients with Hymenoptera sensitivity, there was no clinical history of reaction to horsefly bite despite the presence of positive prick and/or positive intradermal tests and/or positive RAST to mixed Tabanidae species extract.

Conclusions: Skin testing to horsefly by prick and/or intradermal testing using whole body insect extract is not useful in making a diagnosis of Tabanidae hypersensitivity. RAST using Tabanidae species as antigen is similarly useless in making a diagnosis of Tabanidae hypersensitivity. In vivo and in vitro diagnosis of horsefly hypersensitivity may be achieved when the salivary gland antigen of the horsefly becomes available.