Description

• Arthropods are the largest division of the animal kingdom. Two classes, insects and arachnids, have the greatest impact on human health. Arthropods affect humans by inoculating venom, microorganisms, 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 include:
  • Local redness with itch, pain, and swelling: common, usually immediate and transient; large local reactions that increase over 24 to 48 hours; systemic reactions with anaphylaxis, neurotoxicity, organ damage, or other systemic toxin effects; tissue necrosis or secondary infection

Epidemiology

Incidence
Arthropod bites and stings account for up to 1 million emergency department visits annually in the United States.

Prevalence
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 or venom 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.

Genetics
Family history of atopy may be a factor in the development of more severe allergic reactions.

Risk Factors

Previous sensitization; although most arthropod contact is inadvertent, certain activities, occupations, and travel exposures increase risk; greater risk for adverse outcomes in young, elderly, immunocompromised, and those with chronic or poorly controlled cardiac or respiratory disease; increased risk of anaphylaxis, especially to Hymenoptera stings, in patients with mastocytosis

General Prevention

• Avoid common arthropod habitats.
• Insect repellents (not effective for bees, spiders, scorpions, caterpillars, bed bugs, fleas, ants)
  • N,N-diethyl-meta-toluamide (DEET)
    • Most studied repellent; broadest spectrum of activity against biting arthropods (1)[A]
    • Concentrations of 20–35% offer approximately 5 hours of protection (1)[A]. Safe for children >2 months of age and pregnant and lactating women (1)[A]
  • Picaridin (also known as icaridin)
    • 20% spray comparable to 20% DEET for mosquito and tick protection
  • p-Menthane-3,8-diol (PMD; lemon eucalyptus extract)
    • 30% concentrations give 4 to 5 hours of protection against mosquitoes and ticks. Not for use on children <3 years old
  • There are many other products but lack evidence regarding efficacy, duration of action, and safety.
• 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: advised for all travelers to disease-endemic areas at risk from biting arthropods. Permethrin-treated nets may offer additional protection.
• Risk of tick-borne diseases may be decreased by removal of ticks within 24 hours of attachment.