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Development and Resolution of Cutaneous Lesions Caused by Black Fly Bites (Diptera: Simuliidae)

Black flies, also known as buffalo gnats or turkey gnats, are blood-feeding insects in the insect family simuliidae. Immature black flies breed in fast-flowing water, from which the adults emerge in great swarms (usually) in spring or early summer. Black flies are notorious nuisance pests in certain parts of the world and are vectors of the agent of onchocerciasis in tropical areas. Nuisance biting alone can be serious, even fatal, with many reports of livestock and poultry deaths due to black fly biting.1, 2, 3 Outbreaks were a major problem in the southern United States during the early 20th century1 but disappeared until recently. This reemergence may be due to the elimination of harsh pesticides and the cleaning up of creeks and rivers.

Black fly bite reactions include papules, erythematous wheals, indurations, or extensive swelling of the affected area.4 In addition, adenopathy (black fly stiff neck) may occur from bites on the face, neck, and scalp.2 There are many reports of reactions to black fly biting in the northern United States and other parts of the world,2,5, 6, 7 but none from the southern United States, where black flies have typically not been a problem. Here we carefully document the timeline of bites and subsequent development of cutaneous lesions in an entomologist who was investigating a black fly outbreak along the Pearl River in central Mississippi during the spring of 2018.

Methods

The entomologist bitten by black flies was examined by the second author and bite reactions were described and photographed over the following 72 hours. Samples of the offending insect were collected and identified as Simuliim meridionale.

Results

From March 26 to April 2, at least 10 black fly bites were noted on the patient’s arms, neck, and face. Bite reactions sometimes developed into large indurations by 48 hours (Figure 1). Two bites on the neck were carefully followed for 48 hours (Figure 2). At first, there was nothing but erythema and a small hemorrhagic center. Four hours later, lesions developed into a central wheal with surrounding erythema. The diagnosis was papular urticaria, presumably resulting from hypersensitivity to black fly salivary proteins. A raised urticarial papule developed at each bite site with surrounding erythema that itched intensely. Over the course of 24 hours, the urticarial lesions resolved, leaving only an erythematous flattened lesion. By 48 hours, the lesions had completely faded.

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– Jerome Goddard, PhD, Patricia Stewart, MD, Hunter Deerman, MS, Tina M. Nations, MS, Wendy C. Varnado, PhD

This article originally appeared in the October issue of The American Journal of Medicine.

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