DISCUSSION
The results of our cross-sectional study, which conducted in a group of
children with mosquito allergy, revealed the high frequency of
aeroallergen sensitization along with atopic diseases in the study
population. The diagnostic role of the mosquito commercial extract was
very limited in children. Our results also found out several
associations between the duration of symptoms and the features of skin
reactions after mosquito bites in children with mosquito allergy.
One third of the children had at least one allergic disease such as
allergic rhinitis, asthma or atopic dermatitis. When we tried to compare
our findings with previous studies, we have noticed a lack of studies
that were performed by children with mosquito allergy. The study of
Manuyakorn et al.(10) is the only previous childhood study that presents
the demographic and clinical features of children with mosquito allergy.
They have reported data from 50 Thai children and although they did not
perform skin prick tests with aeroallergens, the frequency of
accompanying atopic diseases was 76% in children with mosquito allergy.
However, the details and the definitions of the atopic diseases were not
described. In the study of Kulthanan et al.(11) which reported the
clinical features of 70 adults with mosquito allergy, 58.6% of the
patients had a personal history of atopy. Similar to our results, nearly
half of the patients had allergic rhinitis. Due to the design of our
study, we have included only healthy children without any
physician-diagnosed allergic disease in the control group. Therefore, a
clear statement regarding the increased prevalence of allergic rhinitis
in children with mosquito allergy cannot be extracted from our results.
Nevertheless, the prevalence of physician-diagnosed allergic rhinitis in
children varies between 8.1%-13.4% according to the results of
previous childhood studies in Turkey (12, 13). In consequence with the
previous studies, it can be speculated that large local reactions and/or
unusual reactions after mosquito bites are more encountered in patients
with allergic diseases. Further studies including children with allergic
diseases and without reactions after mosquito bites are needed to
support this hypothesis.
The prevalence of atopy and particularly grass pollen allergy were
significantly more frequent in our cohort of children with mosquito
allergy when compared to healthy children without any unusual reaction
after mosquito bites. We have found a positive relationship between
grass pollen allergy and mosquito reactivity in skin prick tests.
In the study of Kulthanan et al. house dust mite was the most common
allergen in skin prick tests in patients with mosquito allergy (11).
Scala et al. (14) have performed a multicenter study in 205 individuals
reporting large local reactions after mosquito bites and found
significant relationships in SPT reactivity between mosquito
(Aedes communis) and house dust mite (D.pteronyssinus ),
cockroach (B. germanica ), bee (Apis mellifera ) allergens.
They have concluded that in individuals with severe local reactions
following mosquito bites, the immune response to mosquito allergens is
associated with both species-specific and cross-reactive bee venom
components, suggesting the a “bee-mosquito syndrome.” In our cohort,
there was no child with bee or wasp allergy. Nevertheless, only 32
children (34%) had a history of bee and/or wasp sting.
Bemanian et al. have investigated the prevalence of insect aeroallergens
in their cohort of 86 patients (31 children and 55 adults) with allergic
rhinitis (15). Approximately one third of the patients were sensitized
to mosquito allergen in skin prick test. However, there are no data
about the reactions after mosquito bites. Cantillo et al.(16) have
evaluated the cross-reactivity between mosquito allergens (Aedes
aegypti ) and other arthropods in serum samples of 34 patients with
asthma and/or allergic rhinitis and reported a cross-reactivity between
Aedes aegypti and mites, shrimp and cockroach.
Arias-Cruz et al. (17) have aimed to identify the prevalence of mosquito
allergy and performed skin prick tests with a common mosquito species in
Mexico (Aedes aeigypti) in 482 patients ranged in age from 2 to 58
years. Mosquito prick test was positive in 3 of 12 patients (25%) with
large local reactions and no significant difference were found between
patients with or without mosquito allergy. In the childhood study of
Manuyakorn et al., 34% of the children were positive to skin prick test
with Culex pipenes, whereas 32% of the children had positive specific
IgE against Aedes communis . In adults with mosquito allergy the
reported prevalences of positive skin prick tests and positive IgE
antibodies to various mosquito species are higher compared to children
and vary between 46.8-80 % and 45.8-73.8%, respectively (11, 14). The
prevalence of skin prick test positivity to mosquito allergen was 6.4%
in our cohort and there was no difference when compared to control
group. The sensitivity and specificity of currently available tests in
patients with a history of exaggerated or unusual responses to mosquito
bites are reported to be limited (2).
Various researchers have investigated the natural course of reactions
after mosquito bites and classified the patients in 5 stages (18, 19).
Delayed reactions are frequent in children whereas the prevalence of
immediate reactions reported to increase with age during adolescence
(20, 21). In parallel with the previous findings, the majority of the
children in our cohort were in stage 2 and 3 (10, 11). Moreover, we
found out that the children who develop wheals in a short time after
mosquito bites had longer history of symptoms. Erythematous papules were
the most frequent lesions in our group. Another interesting finding of
our study is the significantly higher prevalence of bullous reactions in
children with asthma (41.7% vs.15.9, p=0.034). Bullous reactions to
mosquito bites have been previously reported (22, 23), however there is
no observed association with an atopic background so far. The exact
pathogenesis of the reactions are unknown, however a hypersensitivity
reaction against salivary antigens emerges as a plausible explanation
(24). Severe skin reactions with various systemic symptoms are
encountered in patients with certain conditions such as Epstein-Barr
virus (EBV) associated lymphoproliferative diseases and natural killer
(NK) cell lymphoproliferative disorders. We have consulted the children
in our cohort with our pediatric hematology department and none of the
children in the study group had an underlying hematologic disease during
our follow-up period. Mosquito bites must be kept in mind in the
differential diagnosis of children with bullous reactions and
particularly with asthma.
We did not perform specific IgE testing in our patients, nevertheless
performing these in vivo or in vitro tests especially in young children
may have little benefit. On the other hand, it was performed in a center
which was specialized for children with allergic diseases. The
diagnostic procedures and the longitudinal follow-up of the patients
were made by pediatric allergy specialists. Our study is one of the few
childhood studies that provide unique data about children with unusual
or exaggerated reactions after mosquito bites. Its prospective and
controlled design along with a fairly large number of participants are
other superiorities.
In conclusion, our results indicate that the role of commercially
available tests in the diagnosis of children with mosquito allergy is
limited. There is an association between unusual, large local or
exaggerated reactions after mosquito bites and allergic diseases in
children. The severity of reactions increases with age and particularly
in children with atopic background.