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Term Paper on Schistosoma (Blood Fluke of Man)
Term Paper Contents:
- Term Paper on the Distribution, Habits and Habitat of Schistosoma
- Term Paper on the External Features of Schistosoma
- Term Paper on the Digestive System and Excretory System of Schistosoma
- Term Paper on the Nervous System and Reproductive System of Schistosoma
- Term Paper on the Life History of Schistosoma
- Term Paper on the Pathogenesis and Treatment of Schistosoma
Term Paper # 1. Distribution, Habits and Habitat of Schistosoma:
A number of trematodes inhabit the blood of their host but the best known blood flukes belong to the family Schistosomatidae. The schistosomes of man and other mammals belong to the genus Schistosoma. It causes the human disease schistosomiasis or bilharziasis.
The human blood flukes are the most serious trematode parasites of man since ancient times. They have world-wide distribution. Three important species of schistosoma are known to infect man. S. haematobium is common in Africa, particularly Egypt, and Southwestern Asia.
It inhabits the blood vessels of the bladder and urinary tract. S. mansani occurs in Egypt, parts of South and Central Africa from where it reached West Indies and northern part of South America probably in the days of slavery. It is found in the abdominal cavity of man in the small branches of mesenteric and hepatic portal veins. S. japonicum is found in Japan, China, Celebes and the Philippines. It lives in the small veins of bladder or portal and mesenteric vessels.
Term Paper # 2. External Features of Schistosoma:
Schistosoma is trematode peculiar in many respects. It parasitizes the blood vessels of the host. It is a dioecious, digenetic trematode having separate sexes with a pronounced dimorphism, but the two sexes remain close together in pairs.
Shape and Size and Colour:
Body is thin and cylindrically elongated. The males are comparatively thicker and smaller than the females. The males of Schistosoma haematobium, S. mansoni, and S. japonicum measure 10-15 mm, 6-9 mm and 10-20 mm, in length respectively. The female also varies from 20 to 26 mm in length, according to species.
Body of the parasite is grayish or pinkish in colour. The intestine presents reddish colour due to degenerating blood cells of the host.
The body surface is rough and spiny. In S. haematobium it has fine tubercles, and that of S. mansoni has large tubercles, while that of S. japonicum is non-tuberculate.
In both the sexes, the anterior end carries a small oral sucker surrounding the mouth aperture. A second but large posterior sucker or acetabulum is present ventrally close to the oral sucker.
The mouth opens at the tip of the anterior and surrounded by the oral sucker. The single gonopore lies ventrally just behind the acetabulum. A tiny excretory pore may also be seen ventrally at the posterior end of body.
Schistosoma is unisexual. The male is smaller than the female, which is long and delicate. A thick male permanently carried a slender but longer female in a gynaecophoric canal formed by folding of the ventral body wall.
Term Paper # 3. Digestive System and Excretory System of Schistosoma:
The mouth, surrounded by the oral sucker at the anterior end of the body, leads into a narrow oesophagus. Pharynx is absent. Clusters of oesophageal glands surround the oesophagus which leads behind into intestine. The intestine immediately bifurcates in two branches which reunite in the middle of the body, forming a long and blind ending caecum.
It consists of a bladder with a pair of collecting tubules and flame cells. The excretory products of the flame cells escape through a single minute excretory pore lying ventrally near the posterior end of the body.
Term Paper # 4. Nervous System and Reproductive System of Schistosoma:
As in Fasciola, it consists of a circumoral ring and two lateral longitudinal canals.
The male and female individuals are separate. The male is usually broader and encloses the very slender female in his ventral fold on the body, called the gynaecophoric canals.
(a) Male Reproductive Organs:
The male has four tests; a short vas deferens arises from the testes and joins a seminal vesicle which enters a penis, the penis opens by a gonopore below the acetabulum.
(b) Female Reproductive Organs:
The female has an elongate ovary above the point where the intestinal caeca rejoin, from the ovary an oviduct passes in front. In the posterior third of the female are vitelline glands from which a vitelline duct joins the oviduct. The oviduct meets an ootype surrounded by Mehlis’s gland. From the ootype arises a straight uterus containing a few capsules, it opens by a female gonopore below the acetabulum.
Term Paper # 5. Life History of Schistosoma:
The female is permanently held in the gynaecophoric canal of the male and the paired worms move against the blood stream in a state of permanent copulation.
Fertilization and Ovulation:
Fertilization takes place in the oviduct. Fertilized eggs become encapsulated or shelled by vitelline secretions which also form yolk cells.
The female leaves the body of male and deposits fertilized and shelled eggs, one at a time, in the end of a small vein or venule of the urinary bladder (S. haematobium) or of large intestine. Each egg or capsule contains a miracidium larva. After complete laying of the eggs or capsules, the female moves away.
The shell of the egg bears a spine which facilitates its penetration into the intestine or urinary bladder. By the pressure in the small venule, by the enzymes and by the activity of miracidium larvae contained in the egg capsules, the veins rupture and the eggs escape. In S. mansoni, the eggs are passed into the intestine and escape with the faeces. But in S. haemotobium, they are passed in the urinary bladder and ultimately to outside with the urine.
The eggs measure 170µ in length 112µ in breadth. They contain motile miracidia larvae. The larvae hatch out of the eggs near ditches and ponds, on coming in contact with water.
It measures 130µ in length and 60µ in breadth. The larva contains ciliated epithelial covering. Two pairs of penetration glands occur, one pair anterior and other pair posterior. Miracidium is further characterized by a primitive gut, nerve centre and two pairs of flame cells. Groups of germ cells are also present.
The miracidium larva bores into the body of a freshwater snail and reaches its liver, where it develops into a sporocyst larva. By parthenogenesis, it may produce a second generation of daughter sporocysts. The redia larval stage is absent. The sporocyst develops parthenogenetically into the cercaria larvae.
Body of the cercaria is short and oval with a long forked fail, both covered with minute spines. Oral and ventral suckers are present. The mouth leads into the oesophagus which leads into a trifid intestine, which is the rudiment of the two limbs of intestine. Pharynx is absent. The larva contains an excretory system and nerve elements. There are five pairs of penetration glands-2 pairs of anterior oxyphilic glands and 3 pairs of posterior basophilic glands.
Infection to the Final Host:
The cercariae come out of snails and swim freely in water, and without encysting they penetrate the human skin with great rapidity during bathing or washing or they may be swallowed by drinking infected water. Cercariae enter the blood vessels, go to the heart, then lungs, and then to the liver where they grow; after that they enter the hepatic portal or pelvic veins and become sexually mature.
The cercariae developing from one egg will produce flukes of only one sex, and females do not mature in a host where no males are present. When a male finds a female, it encloses her in the gynaecophoric canal.
Term Paper # 6. Pathogenesis and Treatment of Schistosoma:
The disease is known as Schistosomiasis. In Egypt 69-80% population is affected and at least 10% deaths are caused by these parasites.
The clinical aspect of this disease has three stages as follows:
1. First Stage of the Disease:
Itching is caused by the penetrating cercaria in the skin. The cercariae of a number of blood flukes of aquatic birds can also penetrate human skin, causing dermatitis or skin inflammation that is known as “swimmer’s itch”. Dermatitis requires a week to subside and there are no further pathogenic symptoms. During migration from skin to portal system, they cause headache, general pain, eosinophilia, diarrhea and dysentery.
2. Next Stage of Maturation:
During egg lying, it causes pain in urinary bladder which may develop stones and thrombosis. A kidney trouble with discharge of blood, called haematuria, may be caused. The chief damage is caused by the eggs, deposited in the wall of urinary bladder or intestine before they leave the body in the urine or faeces. Eggs may also be deposited in the arterioles of the lungs causing cardio pulmonary schistosomiasis.
Schistosomiasis can be cured by use of antimony compounds such as tartar emetic, fuadin and anthiomaline. Snails serving as intermediate host can be killed by draining their pastures, by introducing ducks to feed on them or by sprinkling copper sulphate or copper carbonate or contaminated waters. Human infection can be checked by sanitary control of infected water.