Horse Flies: Identification, Bite Reactions, and Clinical Management

Horse flies are common dipteran insects that can be found in most parts of the world. They feed on the blood of their hosts, including humans. Female horse flies pierce the skin of the host, inject anticoagulant saliva, and suck the blood, which can result in minor cutaneous reactions (eg, urticaria, papules localized to the bite site). In severe cases, bites also can result in anaphylaxis. Horse flies can transmit tularemia, which typically manifests as cutaneous ulcers and lymphadenopathy but also can result in severe systemic reactions such as septic shock. Minor cutaneous reactions can be treated with symptomatic management and oral antihistamines, while anaphylaxis and tularemia require systemic therapy with intramuscular epinephrine and intravenous gentamicin, respectively. Exposure to horse flies can be minimized via use of protective clothing, topical repellants, and traps.