Biology Reference
In-Depth Information
syndrome, eosinophilic pneumonitis, or Ascaris pneumonia, is a poten-
tially severe but self-limiting illness associated with the pulmonary
migration of Ascaris larvae. It has been suggested that human infections
with A. suum are more likely to cause a larva migrans syndrome with
pulmonary symptoms.
7,105
A meta-analysis of cross-sectional analyses
showed a positive association between the detection of A. lumbricoides
infections in stool samples and the prevalence of asthma symptoms.
106
Several more recent studies have reported positive associations between
the anti-Ascaris IgE
107
e
109
or active A. lumbricoides infection
110
e
112
and
asthma symptoms or bronchial hyper-responsiveness (BHR)
in low
prevalence populations.
A study in rural Ecuador attributed almost 50% of recent wheeze
cases to the presence of ani-Ascaris IgE but no association was seen with
active infections
113
. Repeated anthelmintic treatments for ascariasis have
been associated with an improvement in asthma symptoms and
a decreased use of asthma medications among asthmatics living in an
area of low prevalence for ascariasis but studies conducted in high
prevalence populations have showed no effect of anthelmintic treatment
on wheeze symptoms.
98,101,102
Asthma symptoms associated with asca-
riasis could be caused by the migration of Ascaris larvae through the
lungs, particularly among those with a tendency to mount allergic
responses to the parasite (i.e. those with anti-Ascaris IgE) or the poten-
tiation of inflammatory responses to other stimuli such as aeroallergens
or endotoxin.
CONCLUSION
The immune response during natural infections with ascariasis in
humans and pigs is associated with the production of Th2 cytokines and,
in some but not all cases, with the elevated production of IL-10 that is
presumed to have an immune modulatory function. Th2 cytokine
response and associated effector mechanisms are considered to mediate
protective immunity to ascariasis in pigs and humans. Some antigen
extracts of A. suum appear to have potent immune modulatory effects in
experimental murine models that may be mediated through IL-10 or
related immune regulatory pathways while other antigens or extracts are
potent initiators of inflammation. There is some, although inconsistent,
evidence that human ascariasis may suppress protective immune
responses to vaccines and immediate hypersensitivity reactions to aero-
allergens in the skin. More consistent are the observations of potent pro-
inflammatory effects of ascariasis in human populations, particularly
among those where the prevalence of infection is high, that cause asthma-
like symptoms through direct or indirect effects. Specific molecules or
