PARA 410 Lecture Notes - Lecture 4: Hymenolepis Nana, Taenia Solium, Intestinal Villus
12 Jun 2018
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Parasitology – lecture 04 (January 15th, 2018)
Review:
- Which Taenia cestode can cause complications in humans; why?
o Port tapeworm causes complications (Taenia solium) because the human can be the accidental
intermediate host by eating the eggs and they can develop the cysticercosis
▪ Accidental host is never good, because it starts to develop in the wrong niche and causes cysts and
other things
- What are the life cycle differences in both species?
o Answer this for practice
- For diagnosis, how can one distinguish between the two Taenia species
o For T. saginata there are more side branches, the eggs are morphologically indistinguishable
- What is the third Taeniidae family member we covered; what is special about the morphology of the adult cestode
o 1 of each body part → E. granulosus/multilocularis
- What are the differences in the juvenile forms of the Taeniidae cestodes we covered?
o Juvenile of Taenia?
▪ Cysticercus
→ cysticercosis
o Juvenile of Echinococcus?
▪ Hydatid cyst
→ Echinococcosis/Hydatid disease
Slide 2
ORDER cyclophyllidea
- Family Hymenolepididae
o Hymenolepis nana - dwarf tapeworm
o Hymenolepis diminuta - rat tapeworm
Slide 3 – Family Hymenolepididae
- Large family of cestodes in birds and mammals
o Characterized by proglottids that are wider than they are long
o Mature proglottids contain a small number of testes (3 or 4)
o Gravid proglottids disintegrate in host and release eggs
- Intermediate hosts are invertebrates
- Family hymenolepididae has only two species that infects humans
o Hymenolepis nana and Hymenolepis diminuta
Slide 4 – Hymenolepis nana
- Hymenolepis nana – dwarf tapeworm
- Has a world-wide distribution and infects mostly children (because they play in dirt)
- Rodents are a reservoir host for this tapeworm (intermediate host to a certain point)
- This is the only tapeworm that does not necessarily need an intermediate host to complete its life cycle
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Slide 5 – Hymenolepis nana
- A small tapeworm (1.5-4.5 cm in length)
- Adult has 150-200 proglottids and lives in the lumen of the small intestine
- Scolex has four suckers and a single row of hooks
Slide 6 – Life cycle
Slide 7 – Hymenolepsis nana Life cycle
- Eggs of Hymenolepis nana are immediately infective when passed with the stool and cannot survive more than 10
days in the external environment (1)
- When eggs are ingested by an arthropod intermediate host (2) (various species of beetles and fleas may serve as
intermediate hosts), they develop into cysticercoids, which can infect humans or rodents upon ingestion (3) and
develop into adults in the small intestine
- When eggs are ingested (4) (in contaminated food or water or from hands contaminated with feces), the
oncosphere contained in the eggs are released
- The oncospheres (hexacanth larvae) penetrate the intestinal villus and develop into cysticercoid larvae. (5)
find more resources at oneclass.com
find more resources at oneclass.com
Slide 8 – Hymenolepsis nana life cycle
- Upon rupture of the villus, the cysticercoids return to the intestinal lumen, evaginate their scoleces (6), attach to
the intestinal mucosa and develop into adults that reside in the small intestine producing gravid proglottids
- Eggs are passed in the stool when released from proglottids through its genital atrium or when proglottids in the
small intestine (8)
- An alternate mode of infection consists of internal autoinfection, where the eggs release their hexacanth embryo,
which penetrates the villus, continuing the infective cycle without passage through the external environment (9)
o The life spam of adult worms is 4-6 weeks, but internal autoinfection allows the infection to persist for
years
Slide 9 – Hymenolepis diminuta
- Hymenolepis diminuta – rat tapeworm → definitive host
- Found throughout the world. Primarily an infection of children
- A small tapeworm (20-40 cm in length)
- Scolex has 4 suckers and 0 hooks
- Many reservoir hosts, including dogs, cats, and many rodent species
Slide 10 – Hymenolepis diminuta – Life Cycle
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
What are the life cycle differences in both species: answer this for practice. For diagnosis, how can one distinguish between the two taenia species: for t. saginata there are more side branches, the eggs are morphologically indistinguishable. What is the third taeniidae family member we covered; what is special about the morphology of the adult cestode: 1 of each body part e. granulosus/multilocularis. What are the differences in the juvenile forms of the taeniidae cestodes we covered: juvenile of taenia, cysticercus. Cysticercosis: juvenile of echinococcus, hydatid cyst. Family hymenolepididae: hymenolepis nana - dwarf tapeworm, hymenolepis diminuta - rat tapeworm. Large family of cestodes in birds and mammals: characterized by proglottids that are wider than they are long, mature proglottids contain a small number of testes (3 or 4, gravid proglottids disintegrate in host and release eggs. Family hymenolepididae has only two species that infects humans: hymenolepis nana and hymenolepis diminuta.
