The undisputed, worldwide success of chemotherapy
notwithstanding, schistosomiasis continues to defy control
efforts in as much rapid reinfection demands repeated treatment,
sometimes as often as once a year. There is thus a need for a
complementary tool with effect for the longer term, notably a
vaccine. International efforts in this direction have been
ongoing for several decades but, until the recombinant DNA
techniques were introduced, antigen production remained an
unsurmountable bottleneck. Although animal experiments have been
highly productive and are still much needed, they probably do not
reflect the human situation adequately and real progress can not
be expected until more is known about human immune responses to
schistosome infection. It is well-known that irradiated cercariae
consistently produce high levels of protection in experimental
animals but, for various reasons, this proof of principle cannot
be directly exploited. Research has instead been focussed on the
identification and testing of specific schistosome antigens. This
work has been quite successful and is already at the stage where
clinical trials are called for. Preliminary results from
coordinated in vitro laboratory and field epidemiological
studies regarding the protective potential of several antigens
support the initiation of such trials. A series of meetings,
organized earlier this year in Cairo, Egypt, reviewed recent
progress, selecteded suitable vaccine candidates and made firm
recommendations for future action including pledging support for
large-scale production according to good manufacturing practice
(GMP) and Phase I trials. Scientists at the American Centers for
Disease Control and Prevention (CDC) have drawn up a detailed
research plan. The major financial support will come from USAID,
Cairo, which has established a scientific advisory group of
Egyptian scientists and representatives from current and previous
international donors such as WHO, NIAID, the European Union and
the Edna McConnell Clark Foundation.
