Aside from being vectors of several of the most important parasitic diseases, including malaria, leishmaniasis, onchocerciasis, filariasis and African trypanosomiasis, mosquitos and other biting flies can induce florid local lesions in susceptible persons. Localized pruritus and urticaria-like papules are the characteristic signs of mosquito bites, while blood-sucking flies induce nodular or haemorrhagic lesions. The muscoid larvae that are responsible for myiasis live parasitically in human tissues. The flies are attracted to festering wounds, ulcers and other necrotic lesions, and they sometimes invade normal tissue. In certain areas of Africa and Central America cutaneous myiasis may occur, which is caused by larvae of the human botfly (Dermatobia hominis). The eggs are laid on the bodies of mosquitos, flies or ticks and subsequently transported to humans. This lesion appears as a folliculitis but exudes a serous fluid, and on close inspection, the larvae may seem to be pulsatile.

Papular urticaria, an insect-related, type IV hypersensitivity reaction, is commonly seen in children in developing countries. It is clinically characterized by crops of pruritic weals that evolve into serum-filled papules and, less frequently, vesicles. Excoriation due to scratching leads to secondary bacterial infections. Spontaneous desensitization usually occurs by the age of 7 years. In tropical climates, mosquitos are the main cause of papular urticaria, whereas flies and bedbugs are the common causes in temperate climates.

Prevention and management

Protection is enhanced by knowledge of the habitat and diurnal activity of the vector. Insect repellents and clothing provide some personal protection.

Screens and bednets impregnated with insecticide can be highly effective when used correctly. Secondary myiasis is rarely seen when good standards of personal hygiene are maintained and wounds are covered to protect them from flies.

For papular urticaria, topical antimicrobials are useful to prevent secondary bacterial infection, and oral antihistamines may relieve the pruritus.