| The general objectives
of this study is to develop and maintain a laboratory based
surveillance program for pertussis and pertussis-like syndrome in
European countries with different vaccination programs and to
identify a possible immunity-driven selection of
B. pertussis variants. In the past few years a divergence
was noted between recent clinical isolates and strains used for
production of Pw and Pa, raising a concern that antigenic
polymorphism might affect the efficacy of pertussis vaccines.
It is, however, still discussed whether this
shift in the population structure of strains is driven by
immunity or is just a co-incidence, and to what extent the
increase of pertussis outbreaks in countries with a traditionally
high vaccine coverage is due to these mutated surface proteins at
the amino acid level. As Pa-vaccines are composed of well defined
components which appear in different subtypes this project offers
a rationale basis to study how strain variation might affect
vaccine efficiency.
Four factors of protein nature have been
identified as critical antigens responsible for inducing immunity
to B. pertussis: pertussis toxin (PT), filamentous
hemagglutinin (FHA), pertactin (PRN) and fimbriae (FIM). They
have been purified and are used in acellular vaccines, which are
now successively replacing the traditional whole-cell vaccines.
Polymorphism has in particular been observed in the genes
encoding for the S 1 subunit of pertussis toxin, for pertactin
and also for the phenotypic expression of fimbriae. In a
surveillance programme, isolates from regions with different
vaccination programmes will be saved and essential vaccine
related components characterized by means of an internationally
accepted standard methodology. The limitations of these
techniques will be addressed to increase capacity.
With new molecular methods it will also be possible to combine
epidemiological typing with etiological diagnosis of agents other
than B.pertussis causing persistent cough. Chromosomal
finger printing will be used to identify unique bacterial clones
causing disease in immunized populations and representative
isolates from such clones selected for “functional”
tests and extended genomic comparisons.
The expected achievements
are:
Achievement 1 to collect B.pertussis and
B. parapertussis strains isolated from vaccinated or
non-vaccinated patients with pertussis disease in countries using
different vaccines and vaccination programmes. Historical
materials will also make it possible to analyse changes over
time.
Achievement 2 to characterize the fimbrial
serotype, the pertactin and pertussis toxin genes as well as
PFGE-patterns by means of the standard methodology.
Achievement 3 to evaluate and validate RT-PCR,
pyrosequencing and flow cytometry for epidemiological typing and
etiological diagnosis of persistent cough.
Achievement 4 to extend genomic analysis of
polymorphic genes coding for surface structures in selected
representative isolates from defined clusters
(“escape”mutants from fully vaccinated individuals
with disease, particularly virulent strains or strains with broad
dissemination) as the pathogenesis of whooping cough is still
incompletely understood.
Achievement 5 to explore genomic differences in
“functional” tests. Mice will be immunized with
different vaccines and challenged with putative
“escape” mutants. Results from this animal model have
been shown to correlate with efficacy studies in humans, and
finally
Achievement 6 to make a synthetic overview and
analysis of the complete research programme and make results
available for scientists, manufacturers and policy makers with an
invitation to extended European networks.
In conclusion the proposal will provide an evidence based
research structure for further improvement of pertussis vaccines.
The programme has a potential to improve surveillance both on
national and European levels.
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