Biology Reference
In-Depth Information
inception, severity, and frequency of allergic episodes is unknown and
other more complex questions persist. For example, urbanization is
associated with higher prevalence of asthma and allergy in developing
countries,
46
but the risk factors leading to this finding remain unclear.
Differences in the level of parasite exposure and intensity of helminth
infections in rural and urban settings could be an explanation. In addition,
to what extent could ascariasis underlie the apparent contradictory fact of
high allergy prevalence in places where, according to the hygiene
hypothesis, the prevalence should be low? These and other questions will
be addressed in the following comments.
ASCARIASIS, ALLERGIC SENSITIZATION,
AND ALLERGY SYMPTOMS
There is a great deal of epidemiological and experimental work, both in
humans and other animals, supporting the idea that ascariasis modifies
the allergic response and the pathogenesis of asthma and other allergic
diseases (reviewed in
47,48
). These investigations have detected that,
depending upon several factors related to the type of parasites, the host,
timing of exposure, infection intensity, and the environment, nematode
infections may induce either severe immunosuppression or enhancement
of the Th2 responses. Ascariasis brings together, but in different propor-
tions, immunomodulation and IgE hyper-responsiveness; the latter is also
a feature of the allergic responses and strongly depends on the genetic
background of the host.
49
The possibility that helminth allergens have an important role in
allergies has been suspected for a long time because there are helminth
infections associated with allergic, IgE-mediated symptoms. The most
typical is anisakiasis that induces an asthma-like syndrome, urticaria and
anaphylaxis.
50,51
In this case, the relationship with allergic symptoms is so
evident that some authors consider it more an allergy condition than an
infection
50
and the list of allergens of
Anisakis simplex
officially accepted by
the WHO/IUIS Nomenclature Committee is the largest for any parasite.
But before anisakiasis was discovered, clinicians from distinct disciplines
had been dealing with hydatidosis, also known as echinococcosis. The
rupture of hydatid cysts that may be located in different places of the body
is a well-known cause of anaphylaxis, bronchospasm, and urticaria.
52,53
In
addition, allergy symptoms associated with the migration of
Strongyloides
spp. and
Toxocara
ssp. are frequently observed in endemic areas
54
e
57
and
adverse allergy symptoms have been described after vaccination with
a recombinant
Ancylostoma
secreted-protein,
Na
-ASP-2.
58
Ascariasis is also a recognized cause of allergy symptoms, including
Loeffler's syndrome.
59
e
61
In addition, there are several human and
