2.4.7 Arthropod reactions

Grading & Level of Importance: B




Ticks, stings, arthropod reaction


Prevalence: hard to estimate because of different types of arthropods and environmental considerations. Most cases do not require medical intervention; more often in tropical climates.


It is necessary to distinguish between:

  1. Reactions to toxins from insect, spider, mites and tick bites
  2. Reactions to bites of parasitic insects, spider, mites and ticks
  • Permanent ectoparasites: parasitic insects (or arachnids = mites, ticks) live and/or feed on humans, are highly adapted and may be found on human hosts.
  • Temporary-accidental ectoparasites: bite humans by chance, the bite reaction varies greatly, and the parasite is rarely found on patients.

Aetiology & Pathogenesis

Human ectoparasites.

Permanent ectoparasites insects: head louse, clothing louse, pubic louse. Arachnids: Demodex and Sarcoptes scabei. Spiders of different types.
Accidental parasitic insects: bed bugs, fleas, mosquitoes, sandflies, gnats, flies and horse flies.

Accidental parasitic arachnids: ticks, Neotrombicula (see Trombiculosis), bites mites (Dermanyssus), non-burrowing animal mites (Cheyletiellidae = walking mange), animal forms of scabies (Sarcoptidae and others).


Sometimes symptoms may be due to neurotoxins.

Signs & Symptoms

Immediate and delayed reactions at site of sting: erythema, macules, papules, wheals and blisters.

The nature of the reaction depends more on the sensitivity of the victim, rather than the nature of the stinging insect.


Exposed skin areas: head, neck, extremities.


See Aetiology and Pathogenesis.

Laboratory & other workups

None specific.


Not necessary.


Varies from self-limited mild local reaction to life threatening anaphylactic reactions.


Persistent arthropod reaction with other complications: pseudolymphomatous reactions, persistent prurigo nodularis-like lesions, secondary bacterial infection. Arthropod borne systemic infections.


Clinical features (grouped or linearly arranged pruritic papules, sometimes with central haemorrhagic punctae (purpura pulicans).

Differential diagnosis

For insect bites reactions: folliculitis, impetigo, furuncle, carbuncle, prurigo, dermatitis herpetiformis, erysipelas, blistering diseases.

Prevention & Therapy

Insect bite reaction from parasitic insects: topical antipruritic agents (zinc oxide lotion, anti-pruritic cream, corticosteroid lotions). Antihistamines in special situations of IgE mediated reactions (e.g. mosquitoes).

Prevention: protective clothing, sleep under fine-mesh nets, repellents.



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