Biology Reference
In-Depth Information
short or long courses of anthelmintics before vaccination.
92
The same
vaccine and vaccine dose showed strong boosting of post-vaccination
IFN-
g
responses in wealthier populations,
93,94
indicating the presence of
a mucosal barrier to oral vaccination among children living in the rural
tropics that, under some circumstances may be accentuated by Ascaris co-
infections, but which are primarily determined by other factors that
interfere between an oral vaccine and the mucosal immune response such
as environmental enteropathy,
89
small intestinal bacterial overgrowth,
95
and intestinal microbiota.
Atopy
Chronic STH infections including ascariasis are associated with the
suppression of allergic inflammatory responses directed against the
parasite
9
although it is less clear if such infections can modulate allergic
inflammation directed against non-parasite allergens such as aero-
allergens that have been most commonly associated with allergic
inflammatory processes (see Chapter 2). Allergic sensitization or atopy in
humans can be determined by measurement of allergen-specific IgE in
serum or skin test reactivity to allergen extracts. Chronic STH infections
are strongly inversely associated with skin prick test reactivity to aero-
allergens (SPT) and protective effects have been shown for A. lumbricoides,
T. trichiura, and hookworm.
96
However, the protective effects of
A. lumbricoides were not independent of those of T. trichiura in studies of
co-infected children in Brazil
97
and Ecuador.
98
If geohelminths were to be
actively suppressing skin test responses, anthelmintic treatment might
be expected to reverse this effect.
Intervention studies have provided evidence that anthelmintic treat-
ment of children may increase SPT,
99
e
101
although a randomized trial in
Ecuador was unable to replicate these findings.
102
The latter trial admin-
istered 400 mg of albendazole every 2 months for a year, and such treat-
ment was much more effective against A. lumbricoides than T. trichiura,
the most prevalent STH infections in the study population.
102
Similarly,
a study of long-term repeated anthelmintic treatments with ivermectin
over a period of up to 15 years showed that such treatment was associated
with an increase in SPT and such effects were primarily attributable to
a lower prevalence of T. trichiura.
98
Thus, it is not entirely clear whether
ascariasis, per se, modulates allergic effector responses against aero-
allergens (i.e. SPT) independent of the presence of other STH infections.
Asthma
Seasonal exposures to ascariasis have been associated with asthma
symptoms for many years.
103,104
The syndrome, known as Loeffler's
