Midge bites: causes, symptoms, diagnosis, and treatment

Midge bites are lesions caused by bites of midges.


Causes

Adult midges are about 1 - 2.5mm in size, black or brown, and often breed in the ponds, swamps, tree caves, stone caves, and shaded moist soil. Their life span is about one month. The eggs are laid in the wet soil, still water, and tree caves. They overwinter as larvae or eggs.

Figure 1 midges sucking blood


Signs and Symptoms

Skin lesions are more common in exposed areas, such as the lower limbs, dorsal feet, forearms, ears, and face, mostly scattered. The subjective symptoms are severe pruritus. Type I lesions are immediate wheals, with traces of bites in the center, reaching a peak within half an hour, subsiding within 24 hours without leaving any traces. Type II lesions are delayed wheals. Edematous erythema occurs 12 - 24 hours after bites, developing wheals, with pea sized, central petechiae or papules, probably evolving into vesicles. In severe cases, there may be angioedema, generalized wheals, and large ecchymoses, progressing into erosion, exudation or secondary infection due to scratches, hot water baths, and stimulations of weeds and sludge in the field. The skin lesions may develop into eczematous dermatitis over time. Prurigo nodularis-like lesions may be present in few patients.

Immunity may be present after 2 - 3 years of repeated attacks, and there are not skin lesions even if midge bites. Therefore, dermatitis after midge bites is more common in individuals without the specific immunity, and residents in the midge areas are mostly asymptomatic after midge bites.


Diagnosis

If there are midges and wheals, the disease can be diagnosed.


Treatment

Dermatitis can be treated with topical 1% phenol or calamine lotion. Secondary infections can be treated with antibiotics. If there are nodules, intralesional prednisolone or triamcinolone can be applied once a week for 2 - 3 weeks. Patients with severe hypersensitivity reactions are administered with oral antihistamines or glucocorticoids.