Immunodominance and Severe Schistosomiasis Mansoni

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Collaborative Course on Infectious
Diseases January 2008
LECTURE 2 Immunodominance and Severe
Schistosomiasis Mansoni
Eduardo Finger ascklepius_at_gmail.com
Harvard School of Public Health Faculdade de
Ciências Médicas da Santa Casa de São Paulo
Brazil Studies Program, DRCLAS, Harvard
University
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Schistosomiasis mansoni
Eduardo Finger Santa Casa SP 2008
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Objectives

• Acquaint students with a basic knowledge of
  schistosomiasis mansoni
• Illustrate the experience of a few countries in
  trying to deal with schistosomiasis
• Discuss what can be learned from these examples
  and how that applies to the project

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• Schistosomiasis
• Second most prevalent tropical parasitic disease
  in the world (behind Malaria only)
• Etiologic agent Schistosoma sp
• 600 million people at risk in 74 countries
• 200.000.000 people infected
• 150.000.000 oligosymptomatic
• 20.000.000 severe disease
• Between 200.000 and 800.000 deaths/year

Disease watch n?4 (Nature reviews microbiology,
January 2004)
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Preferred definitive host of Schistosome sp. in
the wild
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Geographic distribution of schistosomiasis
WHO archives (2002) WHO Technical Report Series,
No.830, 1993
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Spread of S. mansoni followed slave trade routes
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Schistosomiasis route of spread inside Brazil
Memórias do Instituto Oswaldo CruzFundação
Oswaldo Cruz, FiocruzISSN 1678-8060Vol. 99,
Num. s1, 2004, pp. 13-19
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S.mansoni life cycle
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Infection
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Skin penetration by S. mansoni
5min
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Adult worm habitat
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Destination of S. mansoni eggs
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Liver pathology associated with schistosomiasis

• Morbidity and mortality in schistosomiasis are
  due to granulomas formed around parasite eggs

Pipe-stem fibrosis in the liver
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Polar forms of chronic schistosomiasis mansoni

• Intestinal
• Well tolerated, can last years without
  significant harm to host
• Low morbidity and mortality
• Hepatosplenic
• Important inflammation and fibrosis in portal
  spaces
• Extensive liver fibrosis produces portal
  hypertension, splenomegaly, ascites,
  portal-systemic shunting and gastrointestinal
  bleeding
• High morbidity and mortality

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Clinical presentation of severe schistosomiasis
Portal hypertension
Hepatosplenic shunt
Esophageal varices
Hemorrhages
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Treatment and control

• Treatment praziquantel and oxamniquine
• Reinfection rate is very high.
• Vaccine strategy not expected to be available
  soon
• Control strategy massive populational screening
  and treatment. Increase access to treated water.

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Programs to control schistosomiasis

• Four pillars
• Mass chemotherapy (WHO guidelines)
• Molluscicides (chemical and/or biological)
• Sanitation (water and sewer treatment)
• Education
• Other factor
• Urbanization

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Control of Schistosomiasis 4 different
experiences
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Prevalence of schistosomiasis following PECE
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Conclusions from the PECE

• no method is able, in an isolated way, to control
  schistosomiasis and every control program should
  consider the need of multidisciplinary
  application of existing methods
• the main methods for long term control of
  infection are the implementation of basic
  sanitation conditions, potable water supply, as
  well as sanitary education and community
  participation
• specific treatment in endemic areas associated to
  intermediary hosts control in "epidemiological
  important" foci is extremely relevant regarding
  short term morbidity control, though not
  sufficient to interrupt disease transmission
• although schistosomiasis control, in a country
  like Brazil, with great vectors dissemination and
  population mobilization, is a difficult process,
  it is possible through intensification,
  adjustment, and continuity of programs in long
  term
• it is necessary to develop a critical analysis of
  schistosomiasis control experience in Brazil, in
  order to redirect the program in an effective
  way, aiming to achieve only residual levels of
  infection for the next 20 or 30 years or, even
  better, its full control.
• Cienc. Cult. vol.55 no.1 São Paulo Jan./Mar 2003