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Fleas, Mosquitoes, Biting Flies, Bees !!navigator!!

Basics

  • The development of an immediate hive-like skin lesion to a bite or sting (Fig. 29.1) reflects a type I hypersensitivity reaction (mediated by immunoglobulin E).

  • Delayed pruritic papules, nodules, and vesicles usually become symptomatic within 48 hours after an insult and are manifestations of a type IV hypersensitivity reaction (cell-mediated immunity).

Clinical Manifestations

  • Insect bites may be a chronic, recurrent problem or simply a nuisance.

  • Itching may be intense and may persist for weeks.

  • Secondary bacterial infection may occur.

  • Bites often go unnoticed and the lesions that arise from them may not appear for days after the bite (delayed immune-mediated hypersensitivity reaction). Consequently, a patient may seek medical advice for unexplained itchy bumps or blisters.

  • Stings generally cause immediate pain and are therefore usually remembered.

  • A sting can be due to a sting of a bee, wasp, hornet, or yellow jacket. Such stings can be quite painful.

  • A bee sting may trigger a dangerous anaphylactic reaction.

Description of Lesions

  • Bite reactions typically present as intensely pruritic erythematous papules that commonly are excoriated.

  • Such reactions may be indistinguishable from ordinary hives.

  • Grouping of lesions often occurs, particularly after flea bites (“breakfast, lunch, and dinner” lesions [Fig. 29.2]).

  • Lesions may have a central punctum and crust and also may become vesicobullous (Fig. 29.3).

  • Insect bite reactions are also known as papular urticaria when lesions persist for longer than 48 hours.

Distribution of Lesions

  • In general, lesions are found on exposed areas, more often on nonclothed body parts such as the distal lower extremities, the forearms, and hands.

  • Flying insects tend to bite on the upper trunk or extremities, whereas crawling insects tend to bite or sting on the lower trunk or extremities.

  • Axillary and anogenital areas are usually spared.

Diagnosis

  • The diagnosis is usually made on clinical appearance and history.

  • Inquiry about household pets currently and formerly residing in one's house may be a clue to the diagnosis. For example, if the residence was formerly host to a dog or cat infested with fleas, the fleas left behind may have found new human hosts.

  • A skin biopsy is not diagnostic, but it may show suggestive findings consisting of a dense lymphocytic infiltrate (resembling lymphoma) with many eosinophils. The responsible agent is rarely found in a biopsy specimen.

Diagnosis-icon.jpg Differential Diagnosis

Urticaria Unrelated to Insect Bites (Discussed in Chapter 27: Diseases of Cutaneous Vasculature)

  • Often indistinguishable from insect bites; lacks a central punctum.

Fiberglass Dermatitis

  • Nonspecific itching is noted.

  • The patient has a history of exposure (e.g., works with roofing materials).

Scabies (see Discussion later in this chapter)

Helpful-Hint-icon.jpg Helpful Hint

  • Patients who seek medical help generally do not consider the “mundane” nature of insect bites to be the cause of their dermatosis or itching; rather, they seek attention because they assume that other factors caused their problem.

Point-Remember-icon.jpg Points to Remember

  • A careful history and knowledge of the patient's environment and possible exposures should be sought.

  • Symptoms may persist for weeks after the original bites.

  • Other causes should be diligently sought if symptoms persist for more than 4 to 6 weeks.

Management-icon.jpg Management

  • Insect repellents that contain N,N-diethyl-m-toluamide (DEET) help prevent bites and stings.

  • The higher the concentration of DEET, the longer the protection afforded.

  • Picaridin-containing insect repellents have also been shown to be effective.

  • Acute reactions to stings are treated symptomatically with topical or intralesional steroids and/or oral antihistamines; people with severe reactions from stings may profit from desensitization therapy.

  • Anaphylactic reactions require epinephrine, systemic steroids, and antihistamines.

  • If flea infestation is suspected, pets should be evaluated by a veterinarian. If fleas are present in the home, thorough vacuuming and shampooing of flea-infested areas and sometimes even fumigation may be necessary.

Bed Bugs !!navigator!!

Basics

  • Bed bugs (Cimex lectularius) are small insects that feed on human blood. Their preferred habitat is in warm houses and especially nearby or inside of beds and bedding. They often hide in cracks in furniture, floors, or walls.

  • Bed bugs are mainly active at night when people are sleeping. They usually feed on their hosts without being noticed.

  • Adult bed bugs have flat rusty red-colored, flat, oval bodies and are about the size of an apple seed (Fig. 29.4).

  • When bed bugs feed, their bodies swell and become bright red. They can live for a year without feeding on a host.

  • In most cases people carry bed bugs into their homes unknowingly in infested luggage, furniture, bedding, or clothing. Bed bugs may also travel between apartments through small crevices and cracks in walls and floors.

Clinical Manifestations

  • The bites are painless, but later turn into pruritic urticarial papules.

  • Although bed bugs are a great nuisance, they are not known to cause or spread any diseases.

Diagnosis

  • The diagnosis is usually based upon the actual demonstration of the bugs coupled with the clinical findings that are suggestive of bites.

  • Also helpful is seeing small bloodstains from crushed insects, eggs, or dark spots from their feces. White bed sheets help in this recognition.

  • They are often hard to find because they hide in cracks.

  • Detection aides: A bright flashlight, dry ice-baited traps, sticky traps, and detection dogs.

Prevention

  • Clothing should be washed in hot water and dried on the highest dryer setting.

  • Luggage should be inspected immediately after returning from a trip.

  • Areas where bed bugs are likely to hide as well as bedding, linens, curtains, rugs, and carpets should be cleaned thoroughly.

  • Commercially available mattress encasements.

  • Carpets in affected areas should be vacuumed and all debris is placed in taped bags before disposal.

Outline