Protozoal gastroenteritis Flashcards
Acute gastroenteritis & Gardiasis disease are caused by which parasite ?
Giardia Lamblia
Describe the morphology of Giardia Lamblia
- a flagellate that lives in the duodenum and upper jejunum
- 2 forms :
- Trophozoite
- Cyst
Describe the morphology of trophozoite in Giardia Lamblia
- pyriform shaped (half pear) rounded anteriorly and pointed posteriorly
- measures 15 μm x 9 μm
- convex dorsally
- it’s motile, with slow oscillations about its long axis, resembling falling leaf
- Ventrally : has 2 concave sucking discs, which helps in its attachment to the intestinal mucosa
- It is bilaterally symmetrical and possesses:
1. 1 pair of nuclei
2. 4 pairs of flagellae
3. Blepharoplast, from which the flagella arise (4 pairs)
4. 1 pair of axostyles, running along the midline
5. 2 sausage shaped parabasal or median bodies, transversely posterior to sucking disc
Describe the morphology of cystic form in Giardia Lamblia
- infective form of the parasite
- small and oval
- measuring 12 μm x 8 μm
- surrounded by a hyaline cyst wall
- internal structure includes 2 pairs of nuclei grouped at one end
- axostyle lies diagonally, forming a dividing line within cyst wall
- Remnants of the flagella and the sucking disc may be seen in the young cyst
Mode of transmission in G.lambila.
- by ingestion of cysts in contaminated water and food
- Giardia passes its life cycle in one host (humans only)
- Children are commonly affected
Explain the life cycle of G. lamblia
- Within half an hour of ingestion :
* cyst hatches out into two trophozoites
* multiply successively by binary fission
* colonize in the duodenum and upper part of jejunum - Due to unfavorable conditions, encystment occurs usually in colon
- Cysts are passed in stool and remain viable in soil and water for several weeks
Pathogenicity of G. lamblia
- does not invade the tissue, but remains tightly adhered to intestinal epithelium by means of the sucking discs
- affects brush border epithelium of intestine leads to ——> deficiency of enzymes and interferes with intestinal absorption
- Variant-specific surface proteins (VSSPs) of Giardia play an important role in virulence and infectivity of the parasite
- Antigenic variation helps the parasite in evasion of host immune system
Clinical features of G.lambila
- Mostly asymptomatic
- in some cases, Giardia may lead to :
* mucus diarrhea
* fat malabsorption (steatorrhea)
* dull epigastric pain
* flatulence - stool is frothy and contains excess mucus and fat but no blood
- Children may develop :
* chronic diarrhea
* malabsorption of (fat, vitamin A, vitamin B12, folic acid, proteins, sugars)
* weight loss - Chronic giardiasis : may be due to failure to develop immunoglobulin A (IgA) against specific Giardia antigen
What diagnosis is done for G.lambila ?
- Stool Examination:
- identification of cysts in the formed stools and the trophozoites and cysts in diarrheal stools
- macroscopic examination :
- fecal specimens have an offensive odor, are pale colored, fatty, and float in water
- microscopic examination:
- cysts and trophozoites can be found in diarrheal stools by saline and iodine wet preparations
- Often multiple specimens need to be examined.
- In asymptomatic carriers, only the cysts are seen
State the morphology of Trophozoites
- vegetative or growing stage of the parasite
- the only form present in tissues
- irregular in shape and varies in size from 12–60 μm ( average being 20 μm)
- actively motile in freshly-passed dysenteric stool
- Cytoplasm: Outer ectoplasm is clear, transparent, and refractile
- Inner endoplasm: is finely granular, having a ground glass appearance
- endoplasm : contains nucleus, food vacuoles, erythrocytes, occasionally leucocytes, and tissue debris
What is the disease caused by Entamoeba histolytica?
Ameobic dysentery
Describe Pseudopodia structure in Entamoeba histolytica
- finger-like projections formed by sudden jerky movements of ectoplasm in one direction
- followed by the streaming in of the whole endoplasm
- direction of movement may be changed suddenly, with another pseudopodium being formed at a different site
- formation and motility are inhibited at low temperatures
Describe the structure of Entamoeba histolytica nucleus
- has cartwheel appearance: central karoyosome
- surrounded by clear halo
- anchored to the nuclear membrane by fine radiating fibrils
Mention trophozoites of Entamoeba histolytica
- a diagnostic feature——> acute dysenteric stools often contain phagocytosed erythrocytes
- divide by binary fission in every 8 hours
- Infection is not transmitted by trophozoites 🛑
What is the fate of trophozoites?
- Trophozoites survive up to 5 hours at 37°C and are killed by drying, heat, and chemical sterilization
- They are rapidly destroyed in stomach and cannot initiate infection
Describe the cyst in Entamoeba histolytica
- spherical in shape
- about 10–20 μm in size
- early cyst:
- single nucleus
- a mass of glycogen
- 1–4 chromatoid bodies or chromidial bars
- Mature cyst :
- glycogen mass and chromidial bars disappear
- the nucleus undergoes 2 successive mitotic divisions ——> form 2 and then 4 nuclei
- quadrinucleate
- cyst wall :
- highly resistant to gastric juice and unfavorable environmental conditions
Explain the infective form life cycle of E. histolytica
- Mature quadrinucleate cyst passed in feces.
* The cysts can remain viable under moist conditions for about 10 days
How is E.histolytica transmitted?
- Man acquires infection by swallowing food and water contaminated with cysts
- Mostly; E.histolytica remains in the large intestine without causing any illness —-> Such persons become carriers or asymptomatic cyst passers
- cysts pass through the stomach undamaged and enter the small intestine ( resistant to action of gastric juice)
- Excystation: cyst wall is damaged ——-> due to alkaline medium at lower part of the ileum
- Metacyst stage —-> Quadrinucleate ameba is liberated
- The nuclei in the metacyst immediately undergo division to form —-> 8 nuclei ( each gets surrounded by its own cytoplasm to become 8 small amoebulae or metacystic trophozoites)
- Some develop into cysts, which are passed in feces to repeat the cycle
Habitat of metacystic trophozoite
mucosal tissue of caecum and colon
Explain how Intestinal Amoebiasis cause disease
- Amoebae cause disease only when they invade the intestinal tissues
- Penetration of the amoeba is facilitated by the motility of the trophozoites and the tissue lytic enzyme, histolysin ( damages the mucosal epithelium)
- Amoebic lectin another virulence factor mediates adherence
- amoeba penetrates to sub mucosal layer and multiplies rapidly, causing —-> lytic necrosis and thus forming —-> an abscess
The abscess breaks down to form —-> an ulcer - Flask-shaped Amoebic ulcer:
is the typical lesion in intestinal amoebiasis. The intervening mucous membrane between the ulcers remains healthy - Amoebae are seen at the periphery of the lesions and extending into the surrounding healthy tissues
Mention all the Extraintestinal Amoebiasis
- Hepatic Amoebiasis (amoebic liver abscesses)
- Pulmonary Amoebiasis
- Metastatic Amoebiasis
- Cutaneous Amoebiasis
Describe Pulmonary Amoebiasis
May occur:
- hematogenous spread from the colon
- most often follows extension of hepatic abscess through the diaphragm
- lower part of the right lung is the usual area affected
- Hepatobronchial fistula usually results with expectoration of chocolate brown sputum.
Describe Hepatic Amoebiasis
- Enlarged tender liver with the center of the abscess contains thick chocolate brown pus (anchovy sauce pus), which is liquefied necrotic liver tissue
- It is bacteriologically sterile and free of amoeba
- At the periphery, there is almost normal liver tissue, which contains invading amoeba. Usually located in the upper right lobe of the liver
What is Metastatic Amoebiasis?
Abscesses of distant organs is by hematogenous spread and through lymphatics
What is Cutaneous Amoebiasis?
It occurs by direct extension around anus, colostomy site, or discharging sinuses from amoebic abscesses
How to diagnose Intestinal amoebiasis?
By Stool examination
a. Macroscopic appearance:
* stool is foul-smelling, copious, semi-liquid, brownish black in color
* intermingled with blood and mucus. It does not adhere to the container
b. Microscopic appearance: Saline preparation:
- Actively motile trophozoites throwing pseudopodia can be demonstrated in freshly-passed stool. Presence of ingested RBCs clinches the identity of E. histolytica
- Cyst has a smooth and thin cell wall
- at least 3 consecutive specimens should be examined
Diagnosis of Extraintestinal amoebiasis
- Microscopy :
- Liver abscess—-> diagnostic pus aspiration is done, the pus obtained from the center of the abscess may not contain amoeba as they are confined to the periphery
- Aspirates from the margins of the abscess would show the trophozoites
- Cysts are never seen in extraintestinal lesions**
Balantidium coli
- The only ciliate protozoan parasite of humans
- The largest protozoan parasite of humans
- Resides in large intestine of man, pigs, and monkeys
- occurs in 2 stages: trophozoite and cyst
Describe Trophozoite of Balantidium coli
- actively motile and is invasive stage of the parasite found in dysenteric stool
- Motility—> due to the presence of short delicate cilia
- large ovoid cell, about 60–70 μm in length and 40–50 μm in breadth
- anterior end is narrow , there is a groove (peristome) leading to the mouth (cytostome), and a short funnel shaped gullet (cytopharynx)
- posterior end is broad ; there is a small anal pore (cytopyge)
- cilia around the mouth are larger (adoral cilia)
- cell has 2 nuclei:
1. large kidney-shaped macronucleus
2. small micro nucleus ( lying in the latter concavity) - cytoplasm has 1 or 2 contractile vacuoles and several food vacuoles
Describe cyst of Balantidium coli
- cyst is spherical in shape
- measures 40–60 μm in diameter
- surrounded by a thick and transparent double layered wall
- cytoplasm is granular
- Macronucleus, micronucleus and vacuoles are present in the cyst
- found in chronic cases and carriers
What is the natural host in B.coli?
Pig
What is the accidental host in B.coli ?
Man
How humans acquire B.coli?
by ingestion of food and water contaminated with feces containing the cysts of B. coli
- Infection is acquired from pigs and other animal reservoirs or from human carriers
Once the cyst is ingested, excystation occurs in the _________
small intestine
Reservoirs of B.coli
- Pig
2. Monkey
From each cyst, a single______ is produced which migrates to large intestine
trophozoite
Liberated trophozoites multiply in the large intestine by which way?
transverse binary fission
What is the life cycle of B.coli by conjugation?
Sexual union by conjugation also occurs infrequently, during which reciprocal exchange of nuclear material takes place between 2 trophozoites enclosed within a single cyst wall
Encystation in B.coli
- occurs as the trophozoite passes down the colon or in the evacuated stool
- The cysts remain viable in feces for one or two days
When clinical diseases appear from B.coli
Clinical disease results when the resistance of host is lowered, the trophozoites burrow into the intestinal mucosa
This leads to mucosal ulcers and submucosal abcesses, resembling lesions in amoebiasis
What are the clinical features of B.coli
- Most infections are asymptomatic
* Symptomatic disease or balantidiasis resembles amoebiasis causing dysentery with abdominal colic tenesmus nausea and vomiting
B. coli does not invade _______ or any other ______ sites
B. coli does not invade liver or any other extraintestinal sites
How to diagnose B.coli?
By stool examination :
- Motile trophozoites occur in diarrheic feces and cysts are found in formed stools
- The trophozoites can be easily recognized by their large size, macronucleus, and rapid-revolving motility
- The cysts can be recognized in the formed stools by their round shape and presence of large macronucleus
