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بهداشت - Laboratory

بهداشت

بهداشت مواد غذایی وعلوم ازمایشگاهی



CESTODES AND ACANTHOCEPHALANS

 

Objectives: Because the cyclophyllidean tapeworms shed gravid proglottids, you must be able to recognize both the proglottid and the eggs expressed from it in order to diagnosis the infection. Although in many cases the drug used to kill the adult tapeworms works against many cestode species it is important to identify which tapeworm you are dealing with as the intermediate host will be different and, therefore, the control measures will differ for each cestode.

The acanthocephalans are parasites found in a variety of animals, however they are not very important in domestic animals in the United States. In this lab we will present you with the basic structure of the adult acanthocephalan (using the thorny-headed worm of swine as our model) so you will be able to recognize parasites of this phylum if you should ever come across one.

 

Phylum PLATYHELMINTHES

Class Cestoda

Tapeworms of Small Animals

 

Diphyllobothrium latum ([Dog, cat, mink, seal, human] - Cyclops - Fresh water fish Life cycle)

This pseudophyllidean tapeworm utilizes a crustacean as the first intermediate host and fresh water fish as the second intermediate host and paratenic hosts.

A. Adults - DEMO - Notice the large size of this worm and the typical pseudophyllidean segments.

B. Eggs - DEMO - Typical pseudophyllidean eggs. They look like Trematode eggs (60 X 45 :m) and may not float in most common flotation solutions. 

 

Spirometra mansonoides (Cat - Cyclops - Frog or Water snake Life cycle)

This pseudophyllidean tapeworm utilizes a crustacean and a vertebrate (esp. frogs and water snakes) as intermediate hosts.

A. Adults - DEMO - Notice the typical pseudophyllidean segments.

B. Eggs - Bottle #144 (60x35 µm); unembryonated in the feces.   Note: These eggs will not float. (Foreyt pg.59)

 

Echinococcus granulosus (Dog - Sheep Life cycle)

The adult of this small (3 to 4 segments) taeniid tapeworm inhabits the small intestine of dogs, the metacestode (the hydatid cyst) is found in sheep (usually in the liver). This tapeworm is a public health concern as man can be an accidental intermediate host.

A. Adults - Student Slide box #9

Echinococcus granulosus

Adults (Scale is in mm)

Echinococcus granulosus

Stained adult

Echinococcus granulosus

Adults in situ (dog small intestine).

Note the small size; this worm consists of the scolex with 4 suckers and an armed rostellum, an immature proglottid, a mature proglottid containing the genital organs, and a terminal gravid proglottid filled with eggs. Diagram 1 shows a drawing of the internal anatomy of  Echinococcus. This is for your information only.

Remember: Because the eggs in the proglottid are fully embryonated and infectious for humans, the feces of dogs suspected of being infected must be handled with caution. Lab ware, etc., must be sterilized after use or disposed of safely.

B. Larva (metacestode) - Demo of hydatid cysts. These fluid-filled cysts contain many protoscoleces and smaller cysts (brood capsules).

Echinococcus granulosus

Hydatid cysts in the liver of a sheep.

 

Echinococcus granulosus

Hydatid cysts being removed from the liver of a human.

 

Echinococcus granulosus

Diagram of a hydatid cyst.

For an enlarged view click here.

 

Echinococcus granulosus

Cross section of a hydatid cyst.   Host tissue can be seen in the upper left corner, then the wall of the cyst, the germinal layer and finally a daughter cyst, containing protoscoleces, floating free in the fluid-filled interior.

 

Taenia sp. (Dog, Cat - Small Mammal or Human - Livestock Life cycle)

Tapeworms of this genus are found in the small intestine of carnivores and the larval stage is found in various tissues of the mammals that serve as the prey of the carnivore.

A. Eggs - T. saginata - bottle #14 (pg. 33, Foreyt)

All eggs of taeniid tapeworms (Taenia, Echinococcus) look alike. They are round (30-35µm) and have a striated embryophore (shell). Note the six hooks in the oncosphere (embryo), a common feature of all cyclophyllidean tapeworm eggs.

B. Adults - mature proglottids Student-Slide box #1

Note: The reproductive organs within the proglottids and the lateral irregularly alternating genital pores. Diagram 1 shows a drawing of the internal anatomy of a mature proglottid. This is for your information only.

Scolex - Student Slide box #2 (Also see Diagram 1. Note: parts are labeled for your information only.)

Note the 4 suckers; is there a rostellum?

Gravid proglottids Student-Slide box #3

Note: The branched uterus, full of eggs (the number of branches is characteristic of the individual species of Taenia). (Also see Diagram 1. Note: parts are labelled for your information only.)

For a movie of a live, moving Taenia proglottid, Click Here (This is a very large file, do not download with a phone modem).

C. Larva (metacestode) - DEMOS.

The cysticercus (bladder worm) is a relatively small, fluid filled cyst which contains the inverted protoscolex.

Taenia saginata

Cysticerci in the heart of a cow.

 

Taenia saginata

Cysticerci digested free of cow tissue.

Note that many of the protoscoleces have everted.

 

Taenia taeniaformis (Cat - Mouse Life cycle)

Taenia taeniaformis

Adult worms

Taenia taeniaformis

Life cycle

The larval stage in the liver of the mouse is a strobilocercus.

 

Dipylidium caninum (Dog, Cat - Flea Life cycle)

The adult of this cestode is found in the small intestine of dogs (and sometimes children) while the cysticercoid is found in fleas or chewing lice.

A. Adults - Student Slide box #5 and 6

Scolex (SSB #5)               Note: The 4 suckers and armed rostellum.

Dipylidium caninum

Adult worms may reach up to 50 cm in length.

Proglottids (SSB #6)

Note: The bi-convex shape ("cucumber seed"), the duplicated reproductive organs and two lateral genital pores.

Dipylidium caninum

Mature Proglottid

Note: The bi-convex shape ("cucumber seed"), the duplicated reproductive organs and two lateral genital pores.

 

Proglottids on feline feces

At least 7 proglottids can be seen on this fecal specimen.  Four are near the kitty-litter and 3 others are to the right of the kitty-litter.

These are usually noticed by the owner who will tell you they saw "rice grains" or tapeworms in the cat's stool.  The segments may or may not  be in the sample that is brought to you as the proglottids are motile.

B. Eggs - Student Slide box #4 (pg. 33, Foreyt)

The egg packets have been expressed from gravid proglottid.

Dipylidium caninum egg packets.

Note: Each egg packet contains up to 20 eggs and within each is an onchosphere bearing 3 pairs of hooks.  The egg packets pass from the dog within the gravid proglottid, from which they must be expressed for identification.

Note: Each egg packet contains up to 20 eggs and within each is an oncosphere bearing 3 pairs of hooks. Take a proglottid from the dish on the center bench. Place the segment on a slide with a drop of water, place a second slide on top of the segment and apply gentle pressure to straighten it out and flatten it without crushing it. Note the shape and look for the two genital pores (if the proglottid is not gravid these features will be all you have to identify the cestode). Now apply more pressure and crush the proglottid between the two slides and look for the characteristic egg packets that will be released. Note also the calcareous granules found in the parenchyma: these are characteristic of cestodes. (Proglottids dry out quickly, so many times the client presents you with "Sesame-seed"-like objects. These can be re-hydrated by soaking in water for a few minutes and then crushed to release the eggs.)

 

Mesocestoides (Dog, Cat - Arthropod - Vertebrate Life cycle)

This tapeworm utilizes a mite as the first intermediate host and various vertebrates (including dogs and cats) are the 2nd intermediate host. The adult worms are found in the small intestine of dogs in cats.

A. Gravid proglottid - DEMO - note the paruterine organ full of eggs. These proglottids are often "club" shaped.

Mesocestoides corti

Mature proglottid.  Note the paruterine organ (to the left in the photo).  Gravid, "club-shaped" proglottids pass in the feces

Mesocestoides corti eggs

These eggs were expressed from a gravid proglottid.  They measure 40 to 60 µm in diameter.

نوشته شده در یکشنبه 1388/11/18ساعت 13:17 توسط رضوان الله پویا و سجاد رحیمی |


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