Hymenolepis nana
Anticipatory
Objectives
- To identify parasite shape.
- To describe the path of the parasite in human
body.
- To identify the diagnostic and infective stages.
Geographical Distribution
-
It is also known as dwarf tape worm.
-
It is cosmopolitan, more common in warm climate
especially with bad sanitation.
-
It is the commonest tape worm in
Habitat
Adult lives in the small intestine of man, rat and mice (definitive hosts).
Development of H. nana
- Gravid segments detach and disintegrate liberating eggs (diagnostic stage) that pass with faeces.
- Then the development may takes one of the following two easy:
•
Eggs
(infective stages) are immediately infective. When man gets infected,
egg hatches in the small intestine and liberates onchosphere which penetrates
the mucosa and develops into cysticercoid larva.
•
After one week, the cysticercoid
returns to the lumen and develops into adult. Eggs appear in the faeces after
two weeks.
• In children, hyperinfection may
occur due to autoinfection.
• Infection spreads easily between groups of people living together because the eggs are immediately infective.
2. Indirect cycle:
• Sometimes the egg of the parasite is eaten by flea larva or grain beetles (intermediate hosts) in which egg hatches, liberating onchosphere which passes to the body cavity where it develops into cysticercoid. Cysticercoid remains alive until the larva metamorphoses into adult flea.
• When man gets infected, the cysticercoids nana (infective stage) are set free in his small intestine and develop into adult.
*In direct cycle man gets
infected by ingestion of eggs through
→ Contaminated food and drink.
↓
→ External autoinfection (hand to mouth).
*In indirect cycle man is infected by accidental swallowing of these insects with food.
True-False QuestionTrue False
Transition