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Collaborative Course on Infectious Diseases January 2008

LECTURE #2 Immunodominance and Severe Schistosomiasis Mansoni Eduardo Finger ascklepius@gmail.com

Harvard School of Public Health Faculdade de Ciências Médicas da Santa Casa de São Paulo Brazil Studies Program, DRCLAS, Harvard University


Schistosomiasis mansoni

Eduardo Finger Santa Casa SP 2008


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


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)


Preferred definitive host of Schistosome sp. in the wild S. mansoni Group (Restricted to Africa. Only exception: S. mansoni is also prevalent in South America)

S. haematobium Group (Africa, the Mediterranean area and the Middle East) S. haematobium

Parasites humans

S. mansoni

Parasites humans.

S. intercalatum

Parasites humans

S. rodhaini

Parasites rodents and carnivores

S. bovis

Parasites cattle sheep and goats, rarely Man

S. edwardiense

Parasites ruminants

S. mattheei

Parasites primates and ruminants, rarely Man

S. hippopotami

Parasites the hippopotamus

S. curassoni

Parasites ruminants

S. margrebowiei

Parasites ruminants

S. leiperi

Parasites ruminants S. japonicum Group (East Asia)

S. indicum Group (Asia)

S. japonicum

Parasites humans and other animals

S. indicum

Parasites ruminants

S. mekongi

Parasites humans and some other animals

S. spindale

Parasites ruminants and dogs

S. malayensis

Parasites humans (rarely) and other animals

S. nasale

Parasites ruminants

S. sinensum

Parasites rodents

S. incognitum

Parasites rodents, carnivores and ruminants

D. Rollinson and A. J. G. Simpson: 'The Biology of Schistosomes From Genes to Latrines


Geographic distribution of schistosomiasis

WHO archives (2002) WHO Technical Report Series, No.830, 1993


Spread of S. mansoni followed slave trade routes


Schistosomiasis: route of spread inside Brazil

Memórias do Instituto Oswaldo Cruz Fundação Oswaldo Cruz, Fiocruz ISSN: 1678-8060 Vol. 99, Num. s1, 2004, pp. 13-19


S.mansoni life cycle


Infection


Skin penetration by S. mansoni

5min

10min

20 min


Adult worm habitat


Destination of S. mansoni eggs


Liver pathology associated with schistosomiasis • Morbidity and mortality in schistosomiasis are due to granulomas formed around parasite eggs

Normal liver

Pipe-stem fibrosis in the liver


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


Clinical presentation of severe schistosomiasis Portal hypertension

Hepatosplenic shunt

Esophageal varices

Hemorrhages


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.


Programs to control schistosomiasis • Four pillars – Mass chemotherapy (WHO guidelines) – Molluscicides (chemical and/or biological) – Sanitation (water and sewer treatment) – Education

• Other factor: – Urbanization


Control of Schistosomiasis: 4 different experiences

Puerto Rico

Africa

China

Brazil

Program initiation

Goal

Mass treatment

Molluscicide s

Sanitation

Education

Outcome

1953

Reduce prevalence below 4% the erradicate

Yes

Yes

Yes

Yes

Sustained success

50’s

Partial local success but fail overall. Infection on the increase

1949

Temporary. Prevalence on the increase

1976

Partial Success. Reduced prevalence and morbidity

Reduce prevalence below 4% the erradicate

Yes

Yes

No

No


Prevalence of schistosomiasis following PECE


Conclusions from the PECE (a) 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; (b) 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; (c) 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; (d) 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; (e) 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 S達o Paulo Jan./Mar 2003

Lecture 2 schist not good  
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