- Worldwide: More prevalent in the developing world
- More common in warm than in cool climate
Site of infection (Habitat)
- Small intestine especially duodemnum, jejunum and upper ileum
- Swim free, rapidly in spiral motion and attached to intestinal epithelium
- Bile duct and Gall bladder occasionally invaded
- Vegetative form (Trophozoite) --> 7-22microns. Average 14-15 microns
- Cyst form: 10-14 microns
Describe the shape
Oval or pear shaped.
Broad anteriorly, tapering posteriorly.
Flat ventral surface, convex dorsal surface.
Where is the sucking disc?
The anterior portion of the ventral surface. It is bordered by the curved intracytoplasmic portion of the anterior flagella axonem.
Axonems of the caudal pair of flagella are
straight, closely approximated, run parallel to each other dividing the body into two halves through the whole length
What environment favours multiplication?
An alkaline environment, increased by achlorohydra & rich carbohydrate diet
Morphology of the cyst?
1. Oval & the contents are shrunken from cyst wall
2. Four nuclei
3. Axostyle, visible as 2 rods dividing cyst
4. Parabasal bodies cross axostyle
5. Remnants of flagellae, coiled
How is it transmitted?
- Through food and water contaminated with sewage flies or food handlers, and hand to mouth
- It is more common in population groups practising anal-oral intercourse
Pathogenesis: How many cysts are needed, and where does it occur?
- As few as 10 are able to produce infection
- Encystation occurs in the upper regions of the small intestine, where the parasites multiply by simple binary fission
Explain the mechanisms of mucosal injury
1. Attachment of trophozoite to the epithelium can disrupt and distort microvilli
2. Trophozoites produce cytopathic substances responsible for this disruption of epithelial structure and function (proteinases & surface lectin)
3. Mucosal damage occurs by both mechanical and biochemical factors
Explain histological features of the pathology
Shortening of the villi, cellular infiltration of the lamina propria of the mucous membrane
How does it cause diarrhea?
Attachment to mucous membrane --> Inflammation & hyperaemia --> Diarrhea
How does it cause fatty stools and steatorrhea
Associated with inability to absorb fats and vitamin A (malabsorption)
What is the microscopical observation?
Cysts are seen more than trophozoites.
- In diarrheic stools, it is usual to find only trophozoites
- Concentration technique such as zinc sulfate floatation is useful
- No RBCs or Charcot Leyden crystals
Duodenal content may be sampled by the _____ which is gelatin capsule containing a coiled thred