Specific sensitization to the common housefly (Musca domestica) not related to insect panallergy

Background: Allergy to houseflies is rare. We report a case of respiratory allergy from occupational exposure to houseflies in a farmer. Case report: A 30 year-old female farmer with a long-standing history of grass pollen allergy observed for 2 years rhino-conjunctivitis and mild asthma when entering livestock stables and barns. Allergy retesting revealed sensitization to various pollens but not to animal danders. Houseflies (Musca domestica ) occurring on the farm in great quantity were suspected by the farmer herself as the causative agent. Results: Skin prick testing with housefly was positive in the patient and negative in four controls. Experimental radioallergosorbant test was class 3 positive. Sensitization to house dust mite, storage mites and cockroach was not detectable. Western blots with housefly extracts revealed immunoglobulin E (IgE)-binding to bands of 70, 50, and approximately 16 kDa. Tropomyosin in the housefly extract (35 kDa) was recognized by a tropomyosin reference serum but not by the patient. In enzyme-linked immunosorbent assay (ELISA) inhibition assays using housefly as the solid phase, IgE-binding of the patient was inhibited by 75% by M. domestica and by 44% by the closely related lesser housefly (Fannia canicularis ), but not by extracts from blowfly (Lucilia spp.), fruit fly (Drosophila spp.), horsefly (Haematopota pluvialis ) and mosquito (Culex pipiens ). The IgE-binding of the tropomyosin control serum was inhibited by 60-80% by all species. Conclusions: In accordance with previous reports, this case demonstrates that respiratory sensitization to insects may be highly specific. According to ELISA inhibition, cross-sensitization in the present case was restricted to species of the family of true flies (Muscidae ).