Definition
Snail fever, infection with a species of Schistosoma;
manifestations of this often chronic and debilatory disease vary
with the infecting species but depend in large measure upon tissue
reaction (granulation and fibrosis) to the eggs deposited in venules
and in the hepatic portals, the latter resulting in portal
hypertension and esophageal varices, as well as liver damage leading
to cirrhosis.
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Radiographic Appearances
The most common manifestation is of clumps of egg deposits
and associated soft tissue calicifications, the image show below is
from a barium enema examination, showing the chronic granulomatous
deposits in the ascending colon,
Granulomas have also ben seen in the brain on MRI examinations, In
the tumoral form of cerebral schistosomiasis, CT typically reveals a
nodular, noncalcified, nonhemorrhagic, enhancing, space-occupying
lesion with surrounding edema, and MR imaging shows an enhancing
heterogeneous mass with vasogenic edema.
Causes of circumferential bladder wall thickening and bladder
calcifications include acute versus chronic infection or
inflammation from schistosomiasis
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Pathology
Among human parasitic diseases, schistosomiasis (sometimes called
bilharziasis) ranks second behind malaria in terms of socio-economic
and public health importance in tropical and subtropical areas. The
disease is endemic in 74 developing countries, infecting more than
200 million people in rural agricultural and peri-urban areas. Of
these, 20 million suffer severe consequences from the disease and
120 million are symptomatic. In many areas, schistosomiasis infects
a large proportion of under-14 children. An estimated 500-600
million people worldwide are at risk from the disease (map).
Characteristics
The major forms of human schistosomiasis are caused by five species
of water-borne flatworm, or blood flukes, called schistosomes:
Intestinal schistosomiasis caused by Schistosoma mansoni occurs in
53 countries in Africa, the Eastern Mediterranean, the Caribbean and
South America.
Oriental or Asiatic intestinal schistosomiasis, caused by the S.
japonicum group of parasites (including S. mekongi in the Mekong
river basin), is endemic in seven countries in South-East Asia and
in the Western Pacific region.
Another form of intestinal schistosomiasis caused by S. intercalatum
has been reported from 10 central African countries.
Urinary schistosomiasis, caused by S. haematobium, is endemic in 54
countries in Africa and the Eastern Mediterranean.
Schistosomes enter the body through contact with infested surface
water, mainly among people engaged in agriculture and fishing. But
rural-urban migration is introducing the disease into peri-urban
areas in northeast Brazil and Africa, and refugee movements are
spreading it in Somalia and Cambodia. More tourists are contracting
schistosomiasis with the rise in "off-track" tourism, at times with
severe acute infection and unusual sequelae including paralysis of
the legs.
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Treatment:
Three safe, effective drugs --
praziquantel, oxamniquine and metrifonate -- are now available for
schistosomiasis and are included in the WHO Model List of Essential
Drugs.Praziquantel is effective against all forms
of schistosomiasis with few, and only transient, side effects. Cost
has decreased to under US 25 cents for adults and even less for
children. Oxamniquine is used exclusively in Africa and South
America to treat intestinal schistosomiasis. Metrifonate has proved
to be safe and effective for the treatment of urinary
schistosomiasis. Even though re-infection may occur after treatment,
the risk of developing severely diseased organs is diminished and
even reversed in young children. In most areas, a reduction in the
overall number of cases is maintained for 18-24 months and in other
areas for up to five years without further intervention.
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Image
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Useful Link http://www.who.int/health-topics/schisto.htm
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