Case report
Here we report the case of a 51-year-old man, living in Tuscany, Italy (an endemic region for the presence of mosquitoes) who had already begun VIT for Polistes dominula and Vespa crabro after experiencing systemic reactions (grade III according to Muller et al).20
More recently, he experienced two anaphylactic episodes characterized by urticaria, presyncope and ascertained hypotension, during dinner outdoor in summertime.
After a detailed medical history, the patient referred that both reactions took place just after receiving several mosquito bites, which previously provoked only large local reactions. Therefore, mosquito allergy was suspected.
Since skin tests with mosquito extract are no longer available in Italy, specific IgE against Aedes communis were evaluated and resulted increased (0.53 kUA/l, n.v. < 0.35 kUA/l, total IgE 300 kU/l, n.v. < 100 kU/l; ImmunoCAP, ThermoFisher Scientific, Uppsala, Sweden).
Of note, the allergen source of the mosquito ImmunoCAP kit is the insect whole body, instead of its saliva, and this could explain the weak positivity in our patient.
Therefore, the two anaphylactic episodes were interpreted as Mueller IV reactions to mosquito bites.
The allergologic workup included IgE against potential cross-reactive allergens such as tropomyosin and cross-reactive carbohydrate derminants (CCD), which gave negative results.
In the suspicion of a mast cell disorder, serum basal tryptase was evaluated and resulted within normal range; a hematological consultation was performed but bone marrow biopsy was not indicated due to the low probability of a clonal mast cell disorder according to the REMA score (+1).21
The patient was advised to always carry two epinephrine autoinjectors; however, the potential risk of sudden severe allergic reactions to mosquito bites, along with the difficulty in avoiding them, had a major impact on this patients’ QoL.
Therefore, the need for a prophylactic therapy was considered, but its choice was challenging.
The effectiveness of antihistamines has been demonstrated in reducing itching and wheal and large local reactions but not in preventing systemic ones.22,23 An immunotherapy with mosquito extract was not feasible, since its evidence is weak10,11 and, anyway, it is no longer available.
In the absence of other therapeutic options, the patient started off-label therapy with the anti-IgE monoclonal antibody omalizumab, 300 mg subcutaneously every 4 weeks, from August to October 2020.
In this period, he received several mosquito bites without experiencing neither anaphylactic episodes nor mild hypersensitivity reactions.
Given the good result, the therapy was started again in March this year (March to October is the period considered more at risk for mosquito bites in Tuscany), without relapses to date. In parallel, the patient was able to resume outdoor activities and reported a significant reduction of psychological burden of disease.