Tapeworms Taenia saginata and Taenia solium: Morphology, Life Cycle, and Pathogenicity, Lecture notes of Parasitology

Download Tapeworms Taenia saginata and Taenia solium: Morphology, Life Cycle, and Pathogenicity and more Lecture notes Parasitology in PDF only on Docsity!

Taenia solium and Taenia

saginata

Taenia solium

-^ The common name for Taenia solium is pork tapeworm i.e the armedtapeworm of man. •^ The restellum resembles the conventional figures of the sun, hence the name“solium”. •^ It is worldwide in distribution •^ The infection is common amongst those eating raw or insufficiently cookedmeasly pork. •^ It is uncommon in Jews and Mohammeedans who are not generally porkeaters.

Scolex of T.solium

Contd.

-^ The neck is short,measuring from 5 to 10 mm in length. •^ Proglottides- The total number is less than a thousand. •^ A gravid segment measures 12mm by 6mm. •^ The gravid uterus consists of a median longitudinal stem with 5 to 10compound lateral branches on each side. •^ The gravid segments are expelled passively, in chains of 5 to 6 at atime, and not singly.

Contd.

-^ The worm has a life span of as much as 25 years. •^ EGGS-

The characterstics of eggs are as follows:

1.^ Spherical and brown in colour. 2.^ Measures 31-43μm in diameter. 3.^ The thin, outer transparent shell, when present, represents theremnant of the yolk mass; it causes the eggs to clump together. 4.^ The inner embryophore is brown,thick walled and radially striated. 5.^ It contains an oncosphere(14 to20μm in diameter) with 3 pairs ofhooklets. 6.^ Does not float in saturated solution of common salt. 7.^ Eggs are resistant and may remain viable for 8 weeks. 8.^ Eggs are infective to pig as well as to man.

Taenia saginata

-^ The common name is beef tapeworm;the unarmed tapeworm of man. •^ It is worldwide in distribution. •^ In India, it is particularly prevalent amongst Mohammedans. •^ But is not generally found amongst Hindu community who do not as arule eat beef. •^ Adultworm lives in the small intestine of man.

Contd.

-^ Morphology-

Adult worm

-^ It is white and semitransparent,measuring 5 to 10 meters in length butit may be upto 24 metres. •^ The scolex measure 1 to 2 mm in diameter, is quadrate in outline andhas 4 circular suckers. •^ The head is not provided with any rostellum or hooklets. •^ Adult worm moves against the peristaltic movement in the host’sintestine.

Scolex of T.saginata and T.solium

Contd.

-^ The neck is fairly long and narrow. It is fragile. •^ Proglottides- The number varies 1,000 to 2,000. •^ The length of a gravid segment is 3 to 4 times its breadth. •^ When relaxed, the terminal gravid segment measures about 2 cms inlength by 0.5 cm in breadth. •^ The gravid segments are expelled singly and may force their waythrough the anal sphincter often showing great activity outside.

Contd.

-^ The life span of the adult worm is considerable, it may live forupwards of 10 years. •^ Eggs – As there is no uterine opening , the eggs are liberated by therupture of ripe proglottides. •^ Eggs are infective to cattle only. •^ Rest of the characterstics of the egg are same as those for T.solium.

Egg

Contd.

-^ Life cycle of T.saginata

-The worm passes its life cycle in two hosts: 1. The definitive host:man which harbours the adult worm. 2. The intermediate host: Cattle which harbours the larval stage. • The adult worm lives in the small intestine of man. • The eggs or gravid segments are passed out with the faeces on theground. • The animals swallow these eggs while grazing in the field. • On reaching the alimentary canal of the intermediate host, theradially striated walls of the eggs rupture and oncosheres areliberated.

Contd.

-^ These penetrate the gut wall with the aid of their hooks and gainentrance into the portal vessels or mesenteric lymphatics then to thesystemic circulation. •^ The naked oncospheres are filtered out from the circulating blood intothe muscular tissues. •^ Ultimately they settle down in the muscular tissue and undergoesfurther development. •^ The oncospheres lose their hooks on reaching their destination. •^ It takes about 60 to 70 days for the oncospheres to metamorphose intothe cysticercus stage.