Here is a term paper on ‘Echinococcus’. Find paragraphs, long and short term papers on ‘Echinococcus’ especially written for college and medical students.
Term Paper # 1. Habits, Habitat and Distribution of Echinococcus:
Echinococcus granulosus is a minute tape worms 3 to 6 mm long. It is common in Africa, Australia, New Zealand, Iceland, Holland and South America. It is found in hundreds in the intestine of dogs, cats and wolves forming the primary host. The larvae of this parasite develop into hydatid cysts in man, cattle, sheep, pig and other domestic and wild herbivorous animals, forming the secondary or intermediate host.
Term Paper # 2. External Features of Echinococcus:
Shape and Size:
The adult worm is very much like Taenia but differs from it in size. It is very small in size, measuring 2 to 8 mm in length.
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Structure:
The body is divisible into three regions:
1. Scolex
2. Neck
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3. Proglottids or strobila
1. Scolex or Head:
The anterior end of body consists of a knob-like scolex, which anchors the worm to the host’s intestine. It is a highly muscular structure. It measures 500µ in diameter. It is provided with four well-defined adhesive suckers. The rostellum in retractile and contains at its base a double row of 28-50 and 30-36 hooks, respectively.
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2. Neck:
The narrow part of the scolex, behind the suckers, forms the neck. It is the area of strobilization.
3. Proglottids:
There are usually three proglottids— namely first or immature, second or mature and third or gravid proglottid.
(i) First Proglottid:
It is not very distinct. It occurs just below the scolex and is slightly wider than the neck. It has distinct organization except the genital rudiments in the form of dark cells in the centre.
(ii) Second Proglottid:
It is the mature proglottid and contains well-developed genitalia. It is much larger than the first proglottid. There are a large number (20 to 30) of testes. The vas deferens is an extremely coiled tube leading into the genital chamber. There are two compact ovaries. Vitellaria are found below the ovary. Ootype is surrounded by Mehlis’s glands.
(iii) Third Proglottid:
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It is the gravid proglottid. It is much broader and longer than the second proglottid. The main stem of uterus develops indistinct out pocketings containing a large number of eggs. Digestive system, respiratory organs are absent. Excretory system maintains osmoregulation. It consists of excretory canals and flame cells. The nervous system is similar to that of trematodes but not so advanced.
Term Paper # 3. Life History of Echinococcus:
When the uterus of a gravid proglottid bursts, the eggs are liberated and passed out along with faces of dog. The eggs develop into the onchosphere stage. The onchospheres are swallowed as contamination by the intermediate host, which is either man or an herbivorous mammal, such as cattle, kangaroo, sheep or rabbit, etc.
In the duodenum of the host, the embryonic shell is dissolved by the digestive juices and the typical six-hooked embryo (hexacanth) hatches out. The embryo attacks and penetrates the mucosa by its hooks to reach into blood vessels where the hooks are shed.
After 3 hours of egestion, the embryo reaches its final place of development in the lung, liver, kidney or even heart, brain or eye and develops into a large, watery hydrated or bladder. The host forms a fibrous cyst wall around the bladder, which is now called a hydatid cyst.
It grows very slowly in man, but over a period of years it may become enormous in size, sometimes as large as an orange or a football. Developing from a single onchosphere, it is a compound cyst, consisting of cyst within cysts, the smallest of which bear scolices. The multiple scolices present a spiny and berry-like appearance, hence the generic name Echinococcus (Gr., echinos, spiny; occus, berry) of the parasite. Hydatid cysts may be removed by surgery but they are sometimes fatal.
The various kinds of larval cysts, formed in the life history of echinococcus, are as follows:
1. Unilocular Hydatid Cyst:
A unilocular hydatid is spherical in shape and filled with a clear cystic fluid. The cyst wall is made of 3 layers. The innermost layer or endocyst is a thin syncytium forming the germinal layer. The middle layer or ectocyst is cuticular, amorphous and laminated. The outer layer or pericyst is made of connective tissue cells and fibres secreted by the host. The mother cyst also gives rise to several daughter cysts by budding.
The daughter cysts are formed either inside the mother cyst by endogenous budding or on the outside by exogenous budding. The endogenous daughter cysts fall free into the fluid cavity of the mother cyst, while the exogenous daughter cyst, after detachment, migrate to other parts of the body, where they continue to grow further. The daughter cysts possess a fibrous cyst wall lined internally by the syncytial germinal layer or bladder wall.
Rounded and hollow brood capsules are also continuously budded off from the germinal layer of the parent cyst, to which they remain attached for some time by means of a narrow pedicel. In older brood capsules, the inner wall gives rise from 3 to 30 scolices, each connected by a narrow pedicel at least for a time. As new brood capsules continue to grow, the hydatid may increase to enormous size.
When the infective brood capsule is ingested by the final host, each scolex quickly develops into an adult worm and the cycle is repeated.
2. Multilocular Cyst:
They are found in cattle (bovines). It is considered to be the result of differential reaction inside the host. When the growth of the cyst becomes rapid, number of pouches is formed and then it is known as a multilocular cyst.
3. Alveolar Hydatid in Man:
The cyst is of irregular shape, spongy in nature and devoid of cystic fluid. It is commonly sterile and it undergoes degeneration and calcification.
Mode of Infection to Man:
Man obtains infection with too much intimate association with dogs. The tapeworm eggs and proglottids often remain attached to the lips or whiskers of the dogs because of their insanitary habit of licking their posterior ends. Children specially are liable to get infection by allowing dogs to kiss them or by contamination of their food and drinks.
Term Paper # 4. Pathogenesis and Control of Echinococcus:
Pathogenesis:
Cysts are harmful when they develop rapidly. Inflammatory reactions in the surrounding tissues of the host result in the development of fibrous tissue. The osseous tissue is weakened. The liver is enlarged. The presence of cysts in brain or eyes may prove fatal. The escaping hydatid fluid contains toxins and causes vomiting, diarrhoea, abdominal pain, eosinophilia and sometimes collapse.
Control:
(a) Prophylaxis:
1. Avoid playing with dogs.
2. Hands should be thoroughly washed before eating.
3. Dogs should not be allowed to eat raw meat and viscera of sheep, cattle and dogs in endemic areas.
(b) Treatment of Therapy:
1. Surgical:
It is dangerous to remove cysts by surgical methods but the cysts may be killed by injecting them with formalin solution.
2. Areclin Hydrobromide:
One-sixteenth grain per 10 lb weight removes 95% Echinococcus from dogs.