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  Tapeworms and Examples, Biology tutorial

Introduction:

Tapeworms or Cestodes are the most specialized of the Platyhelminthes parasites. All the cestodes encompass at least one and at times more than one, secondary or intermediate host and also their primary host. While the intermediate hosts are mainly invertebrates of some sort, the primary host is in general a vertebrate.

Though, in certain cases both the hosts are vertebrates, as in the common Beef Tapeworm (that is, Taenia saginatus) and in some species there might be just a single host. A number of tapeworms comprise mankind in their life cycles however infection is not usually a serious health problem and can be cured. There are more than 1,000 species of tapeworms acknowledged to science, and almost every species of vertebrate is liable to infection from at least one species of the tapeworm.

Diphyllobothrium latum (the Broad Fish Tapeworm):

Diphyllobothrium latum is the fish tapeworm of the man. It consists of a fairly cosmopolitan distribution, however is mainly common in the Baltic area, Russia and the Great Lakes area of the U.S.A.

Morphology of the adult Tapeworm:

The adult parasites are usually between 2 and 12 m in length by up to 2 cm in width, however might grow even longer in certain cases. The anterior organ of attachment is a Bothria, a pair of shallow, lengthened muscular grooves, typical of tapeworms of the order Pseudophyllidea. The body is splitted into proglottids, as is the case of all pseudophyllidean tapeworms. Such proglottids are wider than they are long, apart from at the terminal end, where they are just about square in shape.

Internally the proglottids are typical of pseudophyllidean tapeworms having numerous testes and vitellaria arranged on the lateral margins of the proglottid having a central bilobed ovary. A significant difference among this parasite and the other tapeworms of man is that the uterus opens to the exterior (that is, cyclophyllidean tapeworms include closed uteruses). Eggs are thus actively deposited by the parasite, in contrast to the disintegration of the proglottids observed in the other human tapeworms. 

Life cycle:

Infection by the adult worm is accomplished through the ingestion of raw, poorly cooked or pickled salmon, trout, pike, perch, Mite fish, eel, grayling, ruff and so on, harboring the plerocercoid larvae. After 5 or 6 weeks, the larva matures to the adult worm. Both the eggs and proglottids are passed in the stool. The eggs build up in 2 weeks, and hatch to become ciliated coracidium larvae and are ingested through the first intermediate host, the copepod. The copepods, having the procercoid larvae are ingested byfisl-t. The second intermediate host encompasses the plerocercoid larvae.

Morphology:

The adult worm reaches up to 10 m having 3,000 proglottids. The scolex is lengthened and spoon shaped with two long sucking grooves. It measures 1 mm in width by 2.5 mm in length. The mature and gravid proglottids are wider than long having the typical rosette-shaped uterus. They measure up to 2 cm in width. The eggs are oval and operculate. They measure 65-70 by 45-50.

Pathology and clinical symptoms:

Symptoms based on the mass of the worm, amount of its by-products absorbed by the host and the susceptibility of host to the foreign substances. A few infected people exhibit no symptoms. There might be intestinal obstruction, abdominal pain, diarrhea and anemia.

Diagnosis:

Diagnosis depends on the recovery of the characteristic eggs or proglottids. Proglottids are frequently passed in chains in a few cm or longer. The proglottid morphology having the rosette-shaped uterus confirms the species.

Prevention:

Avoid ingestion of raw or undercooked trout, salmon, perch and pike.

Dipylidium caninum (the Dog Tapeworm):

This Tapeworm is principally a parasite of the Dog and the Cat. Though, man and in particular children might as well be infected.

Life cycle:

When the eggs are ingested through intermediate host-the larvae of the flea or the dog louse-the oncosphere hatch, go through to the gut and build up into cysticercoids in around 2 weeks. If the infected flea or louse is ingested through a final host that is, dogs, foxes, hyenas, jackals, cats, and humans, the cysticercoids mature to adults in the small intestine in around 20 days. The eggs and gravid proglottids are ejected in the feces.

Morphology:

Adult worms measure 10 to 70 cm in length and 2 to 3 mm in width. The scolex consists of four suckers having 40 to 60 hooklets arranged in 3 to 5 rows around the rostellum. Immature proglottids are trapezoidal, become gradually long with rounded sides toward the posterior end. Mature proglottids have two sets of reproductive organs along with a genital pore on each lateral margin. In the gravid proglottid, eggs are enclosed by thin sacs to make egg-capsules or egg-ball. The eggs are spherical, measuring 40 to 50 pm in diameter. The oncosphere is covered through a thin eggshell and an embryophore.

Pathology and clinical symptoms:

Most of the infected persons are asymptomatic. Severe infection might cause indigestion, diarrhea, abdominal pain, anal pruritus and nervous symptoms.

Diagnosis:

Diagnosis based on the recovery and recognition of gravid proglottids or egg-balls in the stool.

Prevention:

Pets must be kept free of the parasites. The insects must be effectively controlled. The children should be taken safety measures.

Tapeworms of the Genus Hymenolepis:

There are a number of species comprised in this genus, two of which are ordinary parasites of the man.

H. nana - The Dwarf Tapeworm:

Life cycle:

H.nana can build up directly in the small intestine of the definitive hosts and also in an intermediate hosts (that is, insects). When larva-bearing eggs enter the human gastrointestinal tract the oncosphere are discharged into the duodenum and join to the yin where each builds up into a cysticercoid. In 2 to 3 weeks, the cysticercoid builds up into a tapeworm. It is a very common parasite of the house mice and is found in the human, particularly in children.

Morphology:

Adult worm is just 10-45 mm long and 0.5-1 mm wide having 100-200 segments. The eggs (30-50 am) are oval to spherical and nearly colorless.

Pathology and clinical symptoms:

Light infections are asymtomatic. When high numbers of worms are present they might give rise to abdominal pain, headache, diarrhea, anorexia and different non-specific symptoms.

Diagnosis detection of eggs in feces:

Prevention: Personal hygiene, destruction of mice and rats, and a well-balanced diet to encourage resistance to infection.

H. diminuta - The Rat Tapeworm:

This tapeworm is much longer than H. nana, growing up to 60 cm or more in length. This is mainly a parasite of the rat, humans only being infected through accidental ingestion of the insect intermediate host. This species is of more significance as a research model for the study of the physiology, biochemistry, chemotherapy and immunology of the tapeworm infections. In addition there are a number of species found in the animals, comprising:

  • H. carioca: A general non-pathogenic parasite of fowl in the USA. 
  • H. microstoma: A parasite of rodents. 
  • H. lanceolata: A pathogenic parasite of geese, ducks and other anseriform domestic fowl. 
  • H. coronula: A parasite of the anseriform domestic fowl. 
  • H. cantaniana: A parasite of chickens and other galliform domestic fowl.

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