Schistosomiasis

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Collaborative Course on Infectious
Diseases January 2009
LECTURE 7 Schistosomiasis John
David jdavid_at_hsph.harvard.edu Mitermayer
Reis miter_at_cpqgm.fiocruz.br
Harvard School of Public Health Centro de
Pesquisa Gonçalo Moniz, Fundação Oswaldo Cruz
(Fiocruz) Brazil Studies Program, DRCLAS,
Harvard University
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Objectives

• To understand the Schistosomiasis lifecycle,
  which is essential for controlling the disease.
• To consider the factors (e.g., SES,
  environmental) that contribute to the persistence
  of the diseases
• To discuss different control strategies and how
  to prioritize them

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The most important first step to
understand Schistosomiasis and how to control it
is to know the details of the life cycle. The
cycle shows how humans are infected and keep the
cycle going. This is crux for control of the
disease. It should becomes clear that were there
proper sanitation and a supply of clean
water there essentially would be no S. mansoni or
S.hematobium. Control of S.japonicum is more
complicated as it is a zoonosis, water buffalo
and pigs and other animals being involved.
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DISCOVERY OF THE SCHISTOMIASIS PARASITE Bilharz
in 1852 described trematode worms recovered from
postmortems in Egypt, demonstrated
relationship to hematuria and eggs with terminal
spine in the urine. He also described terminal
and lateral spine eggs in the same female worm
and concluded that only one species Infected
man. This was S, hematobium. Manson later
described schistosomiasis in patients in the
West Indies and this was called
S.mansoni. Parajá da Silva in Brazil in1908
described schistosomes which produced lateral
spine eggs and showed that the adults were also
different from S. hematobium, and thus showed
that S.mansoni was a different species.
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These granuloma lead to fibrosis and cause the
pathology you saw in the patient,
The Schistosomes induce this inflammatory
reaction, not to harm their host, but so that
some of the eggs that are swept through the
blood to the bowel can use this inflammatory
process to make their way to the lumen and out
into the water. The pathology thus can be
considered as collateral damage necessary for
their survival. How can we prove
this?
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Mice infected by S.mansoni that lack the capacity
to induce a cell-mediated reaction necessary for
granuloma formation do not excrete the eggs.
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WHY EDUCATING PEOPLE ABOUT HOW THEY GET
INFECTED BY SCHISTOS0MES IS NOT ENOUGH
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THE PRIVATE PLACE AWAY FROM THE CROWD WERE
PEOPLE DEFACATE IN THE STREAM,
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Methods to determine places where cercaria are
present in the water
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Questions for Discussion

• In terms of trying to control Schistosomiasis,
  what would be your top priorities?
• In terms of trying to invest in research, what
  would be your top priorities?