Schistosomiasis
Schistosomiasis
Schistosomiasis is an infection with a relatively low mortality rate but a high morbidity rate; it
is endemic in 74 developing countries, with more than 80% of infected people living in sub-Saharan
Africa. Infection is caused by trematode fl atworms (fl ukes) of the genus Schistosoma: in
freshwater, intermediate snail hosts release infective forms of the parasite.
There are five species of schistosomes able to infect humans:
Schistosoma haematobium (the urinary form) and S.japonicum, S. mekongi, S. mansoni and S. intercalatum (the “intestinal” forms).
If people are in contact with water where infected snails live, they become infected when larval
forms of the parasites penetrate their skin. Later, 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 and S. japonicum), but some eggs
are trapped in body tissues. Immune reactions to eggs lodged in tissues are the cause of disease.
Systemic complications are bladder cancer, progressive enlargement of the liver and spleen,
intestinal damage due to fi brotic lesions around eggs lodged in these tissues, and hypertension
of the abdominal blood vessels. Most cases of cerebral schistosomiasis are observed with
S.
japonicum, constituting 2–4% of all
S. japonicum infections. However, CNS schistosomiasis also
can occur with other species and involves seizures, headache, back pain, bladder dysfunction,
paresthesias and lower limb weakness. Death is most often caused by bladder cancer associated
with urinary schistosomiasis and by bleeding from varicose veins in the oesophagus associated
with intestinal schistosomiasis. Children are especially vulnerable to infection, which develops
into chronic disease if not treated. Diagnosis is made by using urine fi ltration and faecal smear
techniques, antigen detection in endemic areas and antibody tests in non-endemic areas.
The disease is controlled through an integrated approach: drug treatment with praziquantel
or oxamniquine (effective only against
S. mansoni), provision of an adequate safe water supply,
sanitation and health education
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