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Comitê de ética em pesquisa

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Distribution


Endemic in 74 developing countries with more than 80% of infected people living in sub-Saharan Africa.


Causative agent


S. mansoni is found in Africa and is the only species seen in Latin America.


Transmission


Occurs in freshwater when intermediate snail hosts release infective forms of the parasite. People are infected by contact with water where infected snails live. 
Larval forms of the parasites (known as cercariae), released by the snails, penetrate the skin of people in the water. The snails themselves become infected by another larval stage of the parasite, known as a miracidium, which develops from eggs passed out in the urine or faeces of infected people.
S. haematobium is mainly transmitted by Bulinus snails, S. mansoni by Biomphalaria, and S. japonicum by amphibious Oncomelania snails.


Symptoms


Adult male and female schistosomes pair and live together in human blood vessels. The females release eggs, some of which are passed out in the urine (in S. haematobium infection) or stools (S. mansoni, S. japonicum), but some eggs are trapped in body tissues. Immune reactions to eggs lodged in tissues are the cause of disease.
In intestinal schistosomiasis (infection with S. mansoni, S. japonicum, S. mekongi) disease is slower to develop. There is progressive enlargement of the liver and spleen, intestinal damage due to fibrotic lesions around eggs lodged in these tissues, and hypertension of the abdominal blood vessels. Bleeding from these vessels leads to blood in stools, and can be fatal. Sufferers become seriously weakened by the disease and, in some cases, the functioning of organs such as spleen and kidneys becomes impaired.
Death is mostly due to bladder cancer associated with urinary schistosomiasis and to bleeding from varicose veins in the oesopahagus associated with intestinal schistosomiasis. Children are especially vulnerable to infection, which develops into chronic disease if not treated.


Prevention and control


Morbidity control through an integrated approach:
Diagnosis using urine filtration and faecal smear techniques.
serology can be helpful.
antigen detection in endemic areas and antibody tests in non-endemic areas.
Drug treatment with:
praziquantel: effective in a single dose against all species.
oxamniquine: effective in a single dose, but only against S. mansoni.
Snail control through focal mollusciciding.
Provision of safe, adequate water supply and sanitation.
Health education Health education.

Campus Timbiras: Rua Timbiras, 1532, Centro, (31)2103.2103.
Central de Atendimento: Rua Timbiras, 1532, Centro, 1º andar (31)2103.2115.
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