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:
- Reactions to toxins from insect, spider, mites and tick bites
- 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
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
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).
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.
- A patient is stung by a bee in the left leg. Soon thereafter he develops generalized pruritus and shortness of breath, followed by respiratory distress, anxiety and then unconsciousness. What degree of severity is this reaction?
- Statement 1 A acute solitary bullous lesion could represent a reaction to an arthropod bites or sting
- Which complications do not fit with arthropod bites and stings?
- Which clinical finding does not fit with an arthropod bite or sting?
- What other disorders enter into the differential diagnostic considerations when a child presents with periorbital edema and erythema, as shown in the picture?
- What are possible complications of arthropod bites and stings?
- Which therapeutic approach is best for a bite or sting with an excessive local reaction?
- Typical clinical features of arthropod bites and stings are:
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