Arthropod Bites: (Bug Bites, Insect Bites)

Presentation

Patients with bug or insect bites seek medical help because of itching, secondary infection, or anxiety about secondary effects such as communicable diseases or infestation.

Skin lesions generally consist of single or multiple pruritic wheals or papules, which may include excoriations from scratching ( Fig. 164.1 ).

Mosquito bites most often occur on skin-exposed areas in the summer in mosquito-infested environments ( Fig. 164.2 ). Other biting flies include midges, horse flies, deer flies, and black flies .

In tropical and temperate climates, across all socioeconomic strata, bedbugs come out of hiding when their victim has retired to bed ( Fig. 164.3 ). Bites are painless and, unlike lice, the bedbug does not remain on the body after feeding. Bites are usually multiple and may be arranged in an irregular linear fashion. The wheals and papules that form have a small hemorrhagic punctum at the center ( Fig. 164.4 ). Blood that oozes from the wounds may be seen as flecks on the bed sheets. Bullous reactions may follow. There is an apparent resurgence of bedbugs in the United States recently. They are hard to avoid because they may survive without feeding for months even in apparently hygienic circumstances. Avoiding residences with frequent turnover (shelters, hostels, etc.) may mitigate the risk of exposure. Permethrin-sprayed bedclothes or sheets may be effective in prevention.

Kissing bugs are found in the southwestern United States, especially from Texas to California. These large (up to 3 cm in length) winged insects are brown to black, with small stripes of red or orange in some species. The bites of these nocturnal insects occur almost exclusively in rural areas. The painless bite occurs only while the host is sleeping, because the blood meal takes 10 or more minutes to complete. Bites have been associated with papular, urticarial, and bullous reactions, and hemorrhagic wounds that resemble bites of the brown recluse spider have also been reported.

Fleas are small (3 mm long), wingless bloodsuckers capable of jumping to a height of 7 inches. Flea saliva is highly antigenic and is capable of producing a pruritic papular rash. Cat and dog fleas also readily bite people, and thus pets infested with fleas are generally the source of the human rash ( Fig. 164.5 ).

Chigger bites are caused by the harvest mite or red bug, which commonly is found in grasslands of the southeastern United States. The larval form of the mite attaches to the patient’s skin (usually during summer and fall) and sucks up lymph and tissue dissolved by the mite’s proteolytic saliva. Frequently, the only signs of exposure are intensely pruritic papules, 1 to 2 mm in size, on the ankles, legs, or belt line, because the bright red mites typically fall off after feeding. The erythematous papules may persist for up to 3 weeks.

A common hypersensitivity response to arthropod bites (most often caused by fleas or bedbugs) is papular urticaria. The condition consists of small (3–10 mm) pruritic urticarial papules that are present on exposed areas and affect predominantly children between the ages of 2 and 7 years. The papules form in clusters and are characteristically distributed on the extensor surfaces of the arms and legs. The lesions generally persist for 2 to 10 days and may result in temporary hyperpigmentation once they resolve.

Caterpillars have hairs (setae) with irritant and allergenic properties that can cause stinging pruritic erythematous papules, often arranged in linear streaks. Symptoms last a few days to 2 weeks. Whereas pruritus is characteristic of caterpillar dermatitis, the hallmark of the sting of the asp or puss caterpillar is intense pain out of proportion to the size of the lesion produced. A characteristic train-track pattern of purpura often appears at the site of the sting ( Fig. 164.6 ). The range of the puss caterpillar is from Maryland down the eastern seaboard to Florida and across the states bordering the Gulf of Mexico.