Arthropod Bites and Stings
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- Arthropods are the largest division of the animal kingdom. Two classes, insects and arachnids, have the greatest impact on human disease.
- Arthropods affect humans by inoculating poison or irritative substances through a bite or sting, by invading tissue, or by contact allergy to their skin, hairs, or secretions.
- Transmission of infectious microorganisms during feeding is of the greatest concern.
- Sequelae of bites, stings, or contact may include:
- Local redness with itch, pain, and swelling: common, usually immediate and transient
- Large local reactions increasing over 24 to 48 hours
- Systemic reactions with anaphylaxis, neurotoxicity, organ damage, or other systemic toxin effects
- Tissue necrosis or secondary infection
- Infectious disease transmission: Presentation may be delayed weeks to years.
- ~40 deaths per year in the United States from fatal anaphylactic reaction to insects but likely underreported
- Unrecognized anaphylactic reactions to Hymenoptera stings may be cause of 1/4 of sudden and unexpected deaths outdoors.
Widespread, with regional and seasonal variations
Etiology and Pathophysiology
- Arthropods: four medically important classes
- Insects: Hymenoptera (bees, wasps, hornets, fire ants), mosquitoes, bed bugs, flies, lice, fleas, beetles, caterpillars, and moths
- Arachnids: spiders, scorpions, mites, and ticks
- Chilopods (centipedes)
- Diplopods (millipedes)
- Four general categories of pathophysiologic effects: toxic, allergic, infectious, and traumatic
- Toxic effects of venom: local (tissue inflammation or destruction) versus systemic (neurotoxic or organ damage)
- Allergic: Antigens in saliva may cause local inflammation. Exaggerated immune responses may result in anaphylaxis or serum sickness.
- Trauma: Mechanical injury from biting or stinging causes pain, swelling, and portal of entry for bacteria and secondary infection. Retention of arthropod parts can cause a granulomatous reaction.
- Infection: Arthropods transmit bacterial, viral, and protozoal diseases.
Family history of atopy may be a factor in the development of more severe allergic reactions.
- Previous sensitization
- Although most arthropod contact is inadvertent, some activities, occupations, and travel increase risk.
- Greater risk for adverse outcome in young, elderly, immunocompromised, and those with unstable cardiac or respiratory disease
- Increased risk of anaphylaxis in patients with mastocytosis (1)
- Avoid common arthropod habitats.
- Insect repellents (not effective for bees, spiders, scorpions, caterpillars, bed bugs, fleas, ants)
- N,N-diethyl-meta-toluamide (DEET)
- Most effective broad-spectrum repellent against biting arthropods (2)
- Formulations with higher concentrations (20–50%) are first-line choice in areas of endemic arthropod-borne diseases (2).
- Concentrations >30% have longer duration of action.
- Safe for children >6 months of age and pregnant and lactating women (2)
- Icaridin (formerly known as picaridin)
- Concentrations <20% require more frequent applications to maintain activity.
- P-menthane-3,8-diol (PMD-lemon eucalyptus extract)
- IR3535: less effective in most studies
- Other botanical oils (citronella, etc.): less effective than DEET; not for disease-endemic areas
- N,N-diethyl-meta-toluamide (DEET)
- Barrier methods: clothing, bed nets
- Use of light-colored pants, long-sleeved shirts, and hats may reduce arthropod impact.
- Permethrin: synthetic insecticide derived from chrysanthemum plant. Do not apply directly to skin. Permethrin-impregnated clothing provides good protection against arthropods.
- Mosquito nets: Insecticide-treated nets are advised for all travelers to disease-endemic areas at risk from biting arthropods (2).
- Desensitization 75–95% effective for Hymenoptera-specific venom
- Skin tests to determine sensitivity
- Refer to allergist/immunologist.
- Fire ant control (but not elimination) possible
- Baits; sprays, dusts, aerosols; biologic agents
- Risk of tick-borne diseases decreased by prompt removal of ticks within 24 hours of attachment.