Bites, Insect

Essentials of Diagnosis

• Localized urticarial papules with pruritus

• Lesions in linear groups of three ("breakfast, lunch, and dinner") is characteristic of bed bugs

• Furuncle-like lesions containing live arthropods

• Tender erythematous patches that migrate ("larva migrans")

General Considerations

• Body lice, fleas, bedbugs, and mosquitoes should be considered

• Arthropods

  • Most persons can readily detect the bites (eg, mosquitoes and biting flies)

  • However, in other persons, the reaction can be delayed for many hours

  • Many persons are allergic

• Spiders

  • Often incorrectly believed to be the source of bites

  • They rarely attack humans

  • However, the brown recluse spider (Loxosceles laeta, Loxosceles reclusa) may cause severe necrotic reactions and death due to intravascular hemolysis

  • The black widow spider (Latrodectus mactans) may cause severe systemic symptoms and death

• In addition to arthropod bites, the most common lesions are

  • Venomous stings (wasps, hornets, bees, ants, scorpions)

  • Bites (centipedes)

  • Furuncle-like lesions due to fly maggots or sand fleas in the skin

  • Linear creeping eruption due to a migrating larva

• Fleas

  • Ctenocephalides felis and Ctenocephalides canis are the most common species found on cats and dogs

  • Both species attack humans

  • The human flea is Pulex irritans

• Bedbugs are found in crevices of beds or furniture

• Ticks are usually picked up by brushing against low vegetation

• Chiggers or red bugs are larvae of trombiculid mites

• Bird and rodent mites

  • Larger than chiggers

  • Bites are multiple anywhere on the body

• Mites in stored products

  • White and almost invisible

  • Infest products such as vanilla pods, sugar, straw, cottonseeds, cereals

  • Persons who handle these products may be attacked on the hands, forearms and sometimes on the feet

• Caterpillars of moths with urticating hairs

  • Hairs are blown from cocoons or carried by emergent moths, causing severe and often seasonally recurrent outbreaks after mass emergence

  • The gypsy moth is a cause in eastern United States

• Tungiasis

  • Due to the burrowing flea Tunga penetrans and found in Africa, the West Indies, South and Central America

  • The female burrows under the skin, sucks blood, swells to 0.5 cm, and then ejects her eggs onto the ground

Symptoms and Signs

• Individual bites are often in clusters and tend to occur either on exposed parts (eg, midges and gnats) or under clothing, especially around the waist or at flexures (eg, small mites or insects in bedding or clothing)

• The reaction is often delayed for 1–24 h or more

• Pruritus is almost always present and may be all but intolerable once the patient starts to scratch

• Secondary infection may follow scratching

• Urticarial wheals are common; papules may become vesicular

• Flea saliva and bedbugs produce papular urticaria in sensitized individuals

• Chiggers or red bugs

  • A few species attack humans, often around the waist, on the ankles, or in flexures, raising intensely itching erythematous papules after a delay of many hours

  • The red chiggers may sometimes be seen in the center of papules that have not yet been scratched

• Tungiasis: ulceration, lymphangitis, gangrene, and septicemia may result, in some cases with lethal effect

Differential Diagnosis

• Scabies

• Lice

• Fleas

• Bedbugs

• Ticks

• Chiggers or red bugs

• Bird or rodent mites

• Tungiasis (burrowing flea)

• Community-acquired methicillin-resistant Staphylococcus aureus

• Diagnosis is based on the clinical features but may be aided by searching for exposure to arthropods and by considering the patient's occupation and recent activities

Medications

• Corticosteroid lotions or creams are helpful for associated pruritus

• Calamine lotion or a cool wet dressing is always appropriate

• Topical antibiotics may be applied if secondary infection is suspected

• Localized persistent lesions may be treated with intralesional corticosteroids

• Stings produced by many arthropods may be alleviated by applying papain powder (Adolph's Meat Tenderizer) mixed with water, or aluminum chloride hexahydrate (Xerac AC)

• Extracts from venom sacs of bees, wasps, yellow jackets, and hornets are available for immunotherapy of patients at risk for anaphylaxis

• To break the life cycle of the flea, one must repeatedly treat the home and pets, using quick-kill insecticides, residual insecticides, and a growth regulator

Therapeutic Procedures

• Living arthropods should be removed carefully with tweezers after application of alcohol and preserved in alcohol for identification

• Tungiasis: Simple surgical excision is performed

Prevention

• Avoidance of contaminated areas

• Personal cleanliness

• Disinfection of clothing, bedclothes, and furniture as indicated

• Permethrin repels chiggers and mites but not bedbugs

When to Refer

• If there is a question about the diagnosis, if recommended therapy is ineffective, or specialized treatment is necessary