Schistosoma mansoni is geographical located in Africa, especially Egypt and the wet tropical regions, the West Indies, and the eastern coast of tropical South America.
Habitat: Adults found in the haemorrnoidal plexuses of man and of certain species of rodents and baboons.
(b) Eggs are found in feces, rarely in urine and infective only to snail.
(c) All larval stages occur in fresh-water snails, viz. species of Biomphalaria in Africa, and species of Australorbis and Tropocorbis in the American continent.
(d) Infective cercariae escape from the mollusc and have a short free-swimming life in water; they can penetrate the unbroken skin of the final host.
Morphological Characters: The alimentary canal resembles that of S. haematobium except that, in the male. After primary bifurcation, the two limbs of the intestine re-unite in the anterior half of the body. This common caecum usually bifurcates again, the branches re-uniting in a trunk which pursues a wavy course to end blindly near the posterior extremity.
Male: The adult male of schistosoma mansoni measures about 1cm in length and has a breadth of about 1.3mm. Behind the ventral sucker the body is covered with in-numerable tubercles which are distinctly larger than those on the male of S. haematobium. The genital organs resemble those of S. haematobium except that there are eight spherical testes.
Female: The female measures about 1.1cm in length and about 170cm in breadth. The skin is smooth. The ovary is situated in the anterior half of the body, just in front of the junction of the intestinal caeca. In consequence of the anterior position of the ovary, the uterus is short and rarely contains more than three eggs. The vitelline glands occupy the posterior half to two-thirds of the body.
The eggs are bluntly oval, have a lateral spine; and measure about 140cm in length by about 60cm in breadth. The miracidium, sporocyst, and cercaria, resemble those of S. haemotobium very closely.
Life History of Schisitosoma mansoni
The eggs are passed in feces, rarely urine. The succeeding stages are like those of S. haematobium except that development takes place in various species of planorbid snails. As in the case of S. haematobium, the cercariae, after escaping from the snail, die unless they penetrate the final host within some thirty hours. The incubation period in man is about two months. Immunity has been demonstrated in chronic infections, and this is passed to infants before birth and protects them for about six months.
Infection is often subclinical, but in the earlier stages of infection there may be a pronounced eosinophilia, a definite leucocytosis, symptoms of toxaemia such as urticaria, and pulmonary signs. Later, there may be abdominal pain, a pronounced dysentery, blood and mucus being passed in the feces, as a result of the eggs ulcerating through the tissue of the intestine. In very chronic infection there may be prolapse of the rectum. The liver and spleen are enlarged, the former showing cirrhosis.
(a) By finding characteristic, lateral-spined eggs in the feces, particularly in the mucous flakes; eggs occasionally in urine.
(b) By hatching the eggs
(c) By rectal biopsy as already described under the diagnosis of S. haematobium.
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