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Impressive bullous reaction to mosquito bites
  1. Sara Mai,
  2. Siham Mansouri,
  3. Nadia Ismaili and
  4. Karima Senouci
  1. Dermatology, Chu Ibn Sina, Rabat, Morocco
  1. Correspondence to Dr Siham Mansouri; siham-mnsr{at}

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A 34-year-old female patient, with no medical history, presented to our department with large blisters arising from pruritic erythematous swollen patches after mosquito bites. Medical examination revealed multiples tense perfectly hemispherical bullas, sized from 1 to 2 cm, on the inner side of the left knee and thigh overlying large round urticarial plaques (figure 1). The patient stated that she had never experienced a similar reaction to mosquito or any kind of insect bite before. The rest of examination was normal. A complete blood count was performed with no notable abnormalities. The bullas were aseptically pierced and the patient received antihistamines along with local corticosteroids and antiseptics.

Figure 1

Several tense bullas overlying urticarial plaques on the leg.

Local reactions to mosquito bites are very common. They generally manifest as pruritic papules that disappear in few days. Severe reactions, mainly local but also systemic in rare cases, are possible

Common skin manifestations to mosquito bites are either instant hypersensitivity reactions mediated by mast cells resulting in urticarial papules that usually disappear in less than 20 min, or delayed hypersensitivity reaction with pruritic papules that resolves in few days.1

More unusual local reactions have been described such as vesicular or purpuric or bullous reactions, as it was the case in our patient. Systemic reactions are very rare and include fever, angioedema, nausea or even anaphylactic choc.2 3

Only cases with systemic reactions should be considered as allergic to mosquito bites. Several risk factors to these severe reactions have been described such as young age, change of usual environment (immigrants, travellers) and Epstein-Barr virus-associated natural killer/T lymphoproliferative diseases.4 5

Prevention is the most important part of the treatment. Antihistamines and local cortisteroids may decrease the intensity of the skin reactions. Systemic symptoms should be treated according to their severity.4

Learning points

  • Skin reactions to mosquito bites are very variable.

  • Bullous reactions are the most uncommon and can be rather impressive.

  • This benign condition can sometime be the first manifestation of Epstein-Barr virus-associated natural killer/T lymphoproliferative diseases. Therefore, long-time follow-up is essential for these patients.



  • Contributors SaM: contributed in the design, conception and drafting of the paper, participated in the patient’s care. SiM: contributed in the design, conception and drafting of the paper. NI: made the corrections. KS: made the therapeutic decisions and supervised the writting process.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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