Biology Reference
In-Depth Information
asthma have a causal effect upon this disease is unknown, but they are
usually associated to disease severity
29
and there is no evidence of
downregulation in the allergic response in non-parasited populations.
Second, the effector role of specific IgE in ascariasis is less relevant than
in the allergic response. Although specific IgE is involved in protection
against
Ascaris
,
30
e
32
recent discoveries suggest that innate and adaptive
cellular and cytokine networks may be more important for immunity to
helminths.
33
e
36
In contrast, specific IgE to allergens is a central phenotype
of asthma and other allergies, some of them depending on the biological
activity of these antibodies upon histamine-releasing cells, as occurs
during allergic reactions to foods, drugs or other allergen sources. In
summary, although involving common cells and inflammatory mediators,
the immunopathogenesis of helminth infections and allergic diseases has
important qualitative and quantitative differences. Traditionally the two
processes have been considered as very similar; however, recognizing the
differences will help to better understand the
Ascaris
parasitic relation-
ships as well as the evolutionary roots of the allergic response.
ALLER
GIC DISEASES IN TROPICAL RE
GIONS
Although it is believed that allergic diseases are infrequent in under-
developed countries, the fact is that they are very prevalent, especially in
urbanized middle-income areas.
37
The prevalence of asthma and rhinitis
has been evaluated demonstrating that these problems are as frequent as
in industrialized societies
38
e
41
and in some countries they have increased
during the last decade.
42
One particular characteristic of allergic diseases
in the tropics is that sensitizer allergens come mainly from domestic
mites, with pollens, cockroaches, pets, and mold allergens being less
clinically important.
43,44
In addition, the progression of allergic symptoms
during infancy that frequently starts with respiratory symptoms seems to
be different to the “allergic march” observed in European countries,
where atopic dermatitis usually precedes the manifestation of asthma and
rhinits. In a survey covering the general population of Colombia, among
children from 1 to 4 years old, the prevalence of wheeze was 40.1% with
7.6% requiring hospitalization in the last 12 months while the prevalence
of atopic dermatitis was 4.9%.
39
More recently, this pattern was confirmed
in a birth cohort designed to study the allergy symptoms and risk factors
for allergy in the tropics.
45
It is probable that these particularities of allergies in the tropics are
derived from the adverse (and hopefully transitory) circumstance of
permanent exposure to domestic mites and
Ascaris
, two of the most
allergenic sources known. However, the extent of the influence of
helminth infections and mite co-exposure on the prevalence, age of
