Local allergic reactions to fruit flies
Question:
6/25/2019
I have a middle-age female who reports an allergy to gnats, or fruit flies. Based on pictures she develops a large local reaction after being bitten by fruit flies. The literature has very little on this that I could find. The swelling is substantial beyond what I would normally treat with topical corticosteroids. Has anyone seen this before, is there any cross-reactivity is I should watch out for, and what is suggested treatment plan?
Answer:
Diptera or flies can cause local reactions with the biggest responses to deer flies, green flies, black flies and horse flies. Anaphylaxis secondary to fly bites has been described, particularly black flies and deer flies. Fleas, mosquitos, midges and ticks can cause persistent local reactions following a bite, but anaphylaxis has only been reported with ticks and mosquitos. The most well described biting insect responsible for anaphylaxis is the triatoma bug, which is not in the order Diptera (flies) but Hemiptera.
Gnats are in the order Diptera and suborder Nematocera, which includes the separate families of gnats, black flies, crane flies, mosquitos and midges (biting midges are also called no-see-ums). There is no cross reactivity among these to my knowledge. Gnats are smaller than most flies and can cause local reactions following bites but not systemic reactions. Gnats tend to bite less than midges or flies. Some entomologists consider only non-biting flies to be gnats (1). Fruit flies are in a distinct family of Diptera (Drosophilidae), do not bite, do not cause reactions and do not cross react with other biting insects.
I am not aware of any treatment other than high potency topical corticosteroid applied immediately following bites and repeated every 4-8 hours for 1-2 days. I cannot comment on cross-reactivity since I am not sure of which type of insect or insects is causing the reaction. I would encourage insect repellants, such as diethyltoluamide (DEET), before outdoor activity, particularly in the early evening, when bites are likely.
1. https://entomology.ca.uky.edu/ef632
I hope this information is of help to you and your practice.
All my best.
Dennis K. Ledford, MD, FAAAAI