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.