Giardia Duodenalis (Lamblia)

Created by SesterSparrow 

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Notes

Geographical Distribution

- Worldwide: More prevalent in the developing world
- More common in warm than in cool climate

Host

- Man, especially children
- Mice and rats can be infected

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

Size

- Vegetative form (Trophozoite) --> 7-22microns. Average 14-15 microns
- Cyst form: 10-14 microns

How many pairs of flagella?

Four

Describe the shape

Oval or pear shaped.
Broad anteriorly, tapering posteriorly.
Flat ventral surface, convex dorsal surface.

How many nuclei?

two nuclei, each with central karyosome

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.

What is the purpose of the sucking disk?

Attachment (mechanical irritation)

On which surface (ventral or dorsal) are the structures symmetrically represented?

Ventral

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

How does it multiply?

By longitudinal binary fission

What environment favours multiplication?

An alkaline environment, increased by achlorohydra & rich carbohydrate diet

Where is the cyst commonly seen?

In stools

Ecystation starts ____ and proceeds _____.

Starts anteriorly, proceeds posteriorly

The trophozoite in the duodenum encysts by the time they reach the ____

rectum

What kind of stools can the trophozoites be seen in?

Diarrheic stool

Under moist conditions, cysts will ____

remain viable for months outside the host

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

_____ infections are usually asymptomatic

Light

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)

How does it cause peptic ulcer?

Duodenitis and even duodenal ulcer with hunger pains may occur

If it reaches the gall bladder...

give a picture of cholecystitis

The parasite may induce motility disturbances and cause

Abdominal cramps

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
-Fat globules

Duodenal aspiration is more reliable if?

No cysts are passed (contents may be cultured)

Duodenal content may be sampled by the _____ which is gelatin capsule containing a coiled thred

Enterotest capsule

Treatment?

- Metronidazol (Flagyl)
- Tinidazol

Prevention?

- Treatment of cases
- Personal hygeine
- Fly control
- Proper sewage disposal
- Proper water supplies
- Chlorinating water does not kill the cyst, water should be boiled or filtered to remove the parasite

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