STRONA G£”WNA » Subject 8 (Labours, 1st year DDS)

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Subject 8 (Labours, 1st year DDS)


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General characteristics of Cestoda (tapeworms)

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• Tapeworms exhibit a great variety of size.
• The body consist of a scolex, a neck and proglottids (immature proglottids, mature proglottids and gravid proglottids).
• Scolex is equipped with bothria = suctorial grooves, four suckers and hooks for attachment.
• The digestive tract is absent.
• The body wall is covered by a tegument by use of which tapeworms absorb nutrition.
• All species are hermaphroditic.
• The general life cycle involves following stages: egg – oncosphere – larva - the adults.
• All the species of Cestoda are heteroxenous (with exception of Hymenolepis nana).

Diphyllobothrium latum

Kind of parasite: heteroxenous and polyxenous.

Definitive host(s): human and fish-eating mammals.

Intermediate host(s): 1st – copepod, 2st – freshwater fish.

Infective stage: plerocercoid in muscle of fish

Transmission by ingestion of raw fish containing plerocercoids.
Site of infection: the small intestine.

Diagnostic method(s): microscopic identification of eggs or mature proglottids in stool specimens.

Geographical distribution: endemic in northern Europe, Asia, the Arctic and North America.
Remarks:
Prevention consist in protection of freshwater lakes from contamination with untreated sewage and treatment of infected patients. Prevention consist mainly in health education aimed at changing the eating habits.

Taenia saginata

Kind of parasite: heteroxenous and monoxenous.

Definitive host(s): human.

Intermediate host(s): cattle.

Infective stage: cysticercus larva in the muscle of intermediate host.

Transmission by ingestion of raw or poorly cooked beef containing cysticerci.

Site of infection: the small intestine.

Diagnostic method(s): microscopic identification of gravid proglottids (they have 15-30 lateral branches of uterus on each side) in stool.

Geographical distribution: cosmopolitan.

Remarks:
• speciation of Taenia is impossible if solely based on microscopic examination of eggs, because all Taenia species produce the eggs that are morphologically identical;
• prevention consist in treatment of infected individuals, protection of cattle from contamination with human feaces, inspection of beef for cysticerci and refrigeration or cooking of beef.

Taenia solium

Kind of parasite: heteroxenous and monoxenous.

Definitive host(s): human.

Intermediate host(s): pig and sometimes human.

Infective stage: cysticercus larvae (if human is the definitive host); eggs (if human is the intermediate host).

Transmission:
• the definitive hosts (humans) are infected by eating raw or poorly cooked pork containing cysticerci;
• human cysticercosis may occur after the ingestion of eggs or by reverse peristalsis (autoinfection).

Site of infection: the small intestine for adult stage and every organs and tissues for cysticercus larvae.

Diagnostic method(s):
• microscopic identification of gravid proglotids (they have 7-13 lateral branches of uterus on each side) in stool;
• the diagnosis of cysticercosis is made by biopsy, CT and X-ray examination;
• immunological methods.

Geographical distribution: cosmopolitan.

Remarks:
• speciation of Taenia is impossible if solely based on microscopic examination of eggs, because all Taenia species produce eggs that are morphologically identical;
• prevention consist in treatment of infected individuals, protection of pigs from contamination with human feaces, inspection of pork for cysticerci and refrigeration or cooking of pork;

• in the prevention of human cysticercosis early detection and elimination of the infection with adult tapeworm and a high level of personal hygiene (autoinfection is possible) would be of crucial importance.

 Author: Piotr Nowosad date: 2020-05-07  print    back  
 
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