Biology Reference
In-Depth Information
differences between acute and chronic helminth infections with respect to
the effects on inflammation
acute infections appear to be strong
inducers of pro-inflammatory and allergic effects while allergic-type
reactions are rare and may be suppressed during chronic infections.
39
There is some epidemiological data in humans
81
and experimental data in
mice
82
to support the relevance of this paradigm to ascariasis. A number
of clinically relevant effects have been attributed to infections with asca-
riasis including possible impairment of vaccine immunity and effects on
the risk of allergic sensitization (i.e. atopy) and allergic diseases. STH
infections (i.e. Trichuris suis and the hookworm Necator americanus) have
been used experimentally for the treatment of respiratory allergy with
negligible therapeutic effects
83
e
85
and for inflammatory bowel diseases
with at best modest clinical benefit.
86
e
88
There is no evidence to date to
suggest that Ascaris infections are likely to be of therapeutic benefit and
experimental infections with this parasite might be expected to induce
strong inflammatory responses in the respiratory tract of individuals
living in areas where there is little or no transmission of infection. More
promising, perhaps, will be the development of Ascaris-derived molecules
with anti-inflammatory effects for potential therapeutic use.
e
Vaccine Immune Responses
Live attenuated oral vaccines are less immunogenic in poor pop-
ulations in developing countries compared to those living in developed
countries requiring an increase in the dose or number of doses adminis-
tered to achieve adequate vaccine immune responses.
89
It has been sug-
gested that concurrent STH infections might interfere with immune
responses to oral vaccines through effects on mucosal immune
responses.
40,90
A trial in Ecuador that randomized children with ascariasis
to receive anthelmintic treatment or placebo prior to vaccination with
a single dose of a live-attenuated oral cholera vaccine showed that prior
treatment of STH infections enhanced titers of vibriocidal antibodies and
rates of seroconversion.
36
Further, Th1 cytokine responses to cholera toxin
B-subunit, a component of the vaccine used, were elevated after vacci-
nation among children receiving albendazole.
58
Another study, using a similar design, in Ethiopia showed that giving
anthelmintic treatment to individuals with ascariasis before parenteral
BCG vaccination was associated with enhanced IFN-
g
responses to
PPD.
91
However, A. lumbricoides and other STH infections alone are
unlikely to explain impaired immunity to oral vaccines. A recent study
investigating the impact of A. lumbricoides infection on responses to oral
BCG Moreau failed to demonstrate post-vaccination increases in the
frequencies of tuberculin-stimulated PBMCs expressing IFN-
among
children with either active infections or those who had received either
g
