Difference between revisions of "Cyclophyllidea Life-Cycle"

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[[Image:Dipylidium caninum 2.jpg|right|150px|thumb|''Dipylidium caninum'' - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine]]
 
[[Image:Dipylidium caninum 2.jpg|right|150px|thumb|''Dipylidium caninum'' - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine]]
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Indirect with one or more intermediate hosts. When the egg is ingested by the intermediate host, the gastric and intestinal secretions digest the thick shell and activate the 6-hooked oncosphere. Using its hooks, it tears through the mucosa of the host to reach the blood or lymph system, or in the case of invertebrates, the body cavity. Once it has reached its predilection site, the oncosphere loses its hooks and develops, depending on the species, into one of the following larval stages, known as a metacestode. There are six types of metacestode (in increasing order of complexity:
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==Overview==
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Cyclophyllidae cestodes have an indirect life cycle involving one or more intermediate hosts before developing into adult form in the definitive host. Eggs must be ingested by an intermediate host species, once ingested the gastric and intestinal secretions breakdown the thick shell and activate the 6-hooked oncosphere. The oncosphere uses its hooks to tear through the gastrointestinal mucosa to reach the blood or lymph system. In invertebrate hosts the oncosphere will enter directly into the body cavity from the gastrointestinal tract. The oncosphere then travels to its predeliction site, loses its hooks and develops into the larval stage known as a metacestode. This can be one of a number of forms dependant on the species of cestode.
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==Metacestodes==
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There are six types of metacestode (in increasing order of complexity:
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===Cysticercus===
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This is a simple metacestode consisting of a fluid filled bladder containing a single inverted scolex.
  
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1) '''Cysticercus''': a fluid-filled bladder with one inverted scolex
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===Cysticercoid===
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This is a simple metacestode that is only found in invertebrates. It is small, pinhead sized, and instead of a bladder has a potential space containing a single scolex that is not inverted.
  
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2) '''Cysticercoid''': pinhead size; only found in invertebrates; like the cysticercus, but the bladder is reduced to a potential space and the scolex is not inverted
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===Strobilocercus===
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This metacestode is only formed by the cat tapeform ''Taenia taeniaeformis'' and is similar to a cysticercus however the single scolex is attached to the containing bladder by a chain of segments.
  
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3) '''Strobilocercus''': restricted to the cat tapeworm Taenia taeniaeformis; like a cysticercus, but the single scolex is attached to the bladder by a chain of segments
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===Coenurus===
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Similar in form to the cysticercus, however the coenurus contains multiple inverted scolices.
  
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4) '''Coenurus''': like a cysticercus, but has multiple inverted scolices
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===Hydatid cyst===
  
 
5) '''Hydatid cyst''': the metacestode of Echinococcus granulosus; this fluid-filled bladder can grow to the size of a football; it is lined with germinal epithelium that buds off brood capsules internally; inverted scolices form inside these; hydatid sand is the name given to the brood capsules and scolices in the hydatid fluid; the host attempts to wall off the hydatid cyst with fibrous tissue; between this and the germinal membrane is an amorphous layer
 
5) '''Hydatid cyst''': the metacestode of Echinococcus granulosus; this fluid-filled bladder can grow to the size of a football; it is lined with germinal epithelium that buds off brood capsules internally; inverted scolices form inside these; hydatid sand is the name given to the brood capsules and scolices in the hydatid fluid; the host attempts to wall off the hydatid cyst with fibrous tissue; between this and the germinal membrane is an amorphous layer
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3) '''irritation''', e.g. infected flea on animal = exaggerated grooming of animal = swallowed
 
3) '''irritation''', e.g. infected flea on animal = exaggerated grooming of animal = swallowed
  
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[[Category:Cyclophyllidea]][[Category:To_Do_-_Parasites]]
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[[Category:Cyclophyllidea]][[Category:To_Do_-_NickJ]]

Revision as of 10:30, 9 July 2010


 This article is still under construction.


Dipylidium caninum - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine

Overview

Cyclophyllidae cestodes have an indirect life cycle involving one or more intermediate hosts before developing into adult form in the definitive host. Eggs must be ingested by an intermediate host species, once ingested the gastric and intestinal secretions breakdown the thick shell and activate the 6-hooked oncosphere. The oncosphere uses its hooks to tear through the gastrointestinal mucosa to reach the blood or lymph system. In invertebrate hosts the oncosphere will enter directly into the body cavity from the gastrointestinal tract. The oncosphere then travels to its predeliction site, loses its hooks and develops into the larval stage known as a metacestode. This can be one of a number of forms dependant on the species of cestode.

Metacestodes

There are six types of metacestode (in increasing order of complexity:

Cysticercus

This is a simple metacestode consisting of a fluid filled bladder containing a single inverted scolex.

Cysticercoid

This is a simple metacestode that is only found in invertebrates. It is small, pinhead sized, and instead of a bladder has a potential space containing a single scolex that is not inverted.

Strobilocercus

This metacestode is only formed by the cat tapeform Taenia taeniaeformis and is similar to a cysticercus however the single scolex is attached to the containing bladder by a chain of segments.

Coenurus

Similar in form to the cysticercus, however the coenurus contains multiple inverted scolices.

Hydatid cyst

5) Hydatid cyst: the metacestode of Echinococcus granulosus; this fluid-filled bladder can grow to the size of a football; it is lined with germinal epithelium that buds off brood capsules internally; inverted scolices form inside these; hydatid sand is the name given to the brood capsules and scolices in the hydatid fluid; the host attempts to wall off the hydatid cyst with fibrous tissue; between this and the germinal membrane is an amorphous layer

6) Alveolar cyst: the metacestode of Echinococcus multilocularis; this is like the hydatid cyst, but daughter cysts bud off the external, as well as the internal, surface of the germinal layer, with the result that the metacestode expands by infiltrating through the tissue, rather like a tumour.

When the metacestode is ingested by the final host, the scolex attaches to the mucosa, the remainder of the structure is digested, and a chain of proglottids (segments) begins to grow from the base of the scolex.

Infection of the final-host involves at least three epidemiological relationships:

1) predator-prey, e.g. cat eating infected mouse

2) accidental, e.g. horse eating infected pasture mites

3) irritation, e.g. infected flea on animal = exaggerated grooming of animal = swallowed

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