"Allergy" - what is it, definition of the term
A hypersensitivity reaction is an immune‑mediated response in which the body’s defense system mistakenly identifies benign substances—such as proteins in the saliva of ticks, insects, lice, or fleas—as threats, triggering the release of antibodies and inflammatory mediators that produce symptoms ranging from localized itching and swelling to systemic effects like hives, respiratory distress, or anaphylaxis.
Detailed information
Allergic responses to arthropod bites involve IgE‑mediated activation of mast cells and basophils, leading to the release of histamine, leukotrienes, and prostaglandins. The reaction magnitude depends on prior sensitization, bite frequency, and individual immune profile.
Tick bites can trigger localized edema, erythema, and pruritus within hours. In sensitized individuals, systemic manifestations such as urticaria, angio‑edema, and anaphylaxis may develop. Tick saliva contains anticoagulant proteins that enhance antigen exposure, increasing the likelihood of a pronounced immune response.
Bug bites, including those from mosquitoes, sandflies, and bedbugs, often produce a papular rash with central punctum. Repeated exposure may lead to a delayed‑type hypersensitivity characterized by intense itching, vesiculation, and sometimes hyperpigmentation. Certain species transmit pathogens that can amplify the immune reaction.
Louse infestations generate a pruritic papular eruption, especially on the scalp and torso. The mechanical irritation of chewing mouthparts combined with salivary antigens provokes a type I hypersensitivity in many hosts. Secondary bacterial infection frequently complicates the presentation.
Flea bites typically appear as clusters of small, erythematous papules surrounded by a halo of redness. In hypersensitive persons, the lesions may coalesce into larger wheals, accompanied by systemic symptoms such as headache, fever, and malaise. Flea saliva contains proteases that act as potent allergens.
Key clinical features across these arthropod‑induced reactions include:
- Immediate swelling and redness at the bite site
- Intense itching persisting for several days
- Development of wheals or hives beyond the primary lesion
- Respiratory distress or hypotension in severe cases
Diagnosis relies on a detailed exposure history, physical examination, and, when necessary, skin prick or serum-specific IgE testing to identify the responsible antigen. Exclusion of infectious etiologies is essential, as many arthropods serve as disease vectors.
Management strategies consist of:
- Antihistamines to block histamine receptors and reduce pruritus
- Topical corticosteroids to diminish local inflammation
- Systemic corticosteroids for extensive or refractory reactions
- Epinephrine auto‑injectors for patients at risk of anaphylaxis
- Environmental control measures, including regular cleaning, use of insecticides, and protective clothing, to prevent further bites
Preventive approaches focus on reducing host–parasite contact, employing repellents containing DEET or picaridin, and maintaining personal hygiene to limit infestations. Early recognition and prompt treatment mitigate complications and improve patient outcomes.