micro sheet # 3 Dr. 7assan - muna sawwan

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micro sheet # 3 Dr. 7assan - muna sawwan

Post by Shadi Jarrar on 29/4/2011, 3:20 pm

بسم الله الرحمن الرحيم

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In the last two lectures we covered the introduction of parasites and the general morphology of the parasites and we said that there is:
- Protozoa: Unicellular.
- ??? : Multicellular.

Today, we will talk about some individual parasites.

First group: Protozoa.
1) Entamoeba histolytica:
- There are many amoebae that are free living and usually they are not pathogenic "with exception of one or two", but E. histolytica is a harm one for human.
- (As far as you concern as a dental student, you have to know about Entamoeba gingivalis).
- Its found in mouth associated with tooth caries and in people with a very bad oral hygiene, 90% of those people you find it in their oral cavity but it doesn’t cause caries or gingivitis but it lives in that bad environment.
- E. histolytica present in many people, 10% of world population are infected with it (very prevalent), and its usually found in large intestine.
- It has a nucleus which has a central Trophozoite, 20-30µm in diameter and chromatin distributed uniformly around the nucleus membrane.
- Cytoplasm is divided into 2 areas:
a. Clears thinner outer called ectoplasm.
b. Denser inner called endoplasm.
- You know that amoeba uses the pseudopodes to move and infect, this is effective by the ectoplasm.
- Ectoplasm is the mobile of this organ, while in the endoplasm, of course, they have all the organelles for metabolism, and usually in the endoplasm there is a vacuole containing debris and bacteria, and a very specific characteristic feature is the presence of ingested RBCs.

Notes:
- Trophozoite: feed and excrete.
- Amoeba: divide by binary fission.

The infection is very common but the disease is relatively rare, why?
1. Because of the different enzymatic patterns.
2. Some are resistant to lysins by complement system.
3. Environment in which they live dictate the pattern of produced enzymes.
4. Normal Flora in large intestine, amoeba usually grows where bacteria found, and some bacteria may change the enzyme patterns.
So, some may have amoeba but not infected.

- Now, we said that Trophozoite is the one responsible for pathogenicity, but for transmission you need intermediate host. But, here there is no such mean for transforming the whole organism from one person to another, the organism have to change their morphology to cyst with a hard covery and 4 nucleus.
- The cyst pass with feces and if feces contaminate food, then this food is eaten by someone, the cyst go to the stomach and sense they are resistant to acid (not like Trophozoites) they survive and go to the small intestine, and there, under the effect of hydrolytic enzymes the cyst will disintegrate and the 4 nuclei are librated, and will divide very quickly into 8, so 8 amoebae that move quickly to the large intestine.
- Very simple feco-oral transmission with No intermediate host.
- Parasites are either tissue or luminal parasites, Trophozoite is a luminal parasites.

Pathenogenicityof E. histolytica:
- Some peoples consume food with cysts of E. histolytica, but for reasons (not really understood) are not infected, this persons consumed cysts either get the cyst and 4 nuclei or not get any cyst.
- Now, who get the cyst and 4 nuclei is the person who is infected but that doesn't mean that he has the disease. But, in the 2 cases: 1) the majority will not have the disease but considered as a carrier; 2) some have the disease (desentry).

What desentry means:
It’s a bloody diarrhea that has pus and mucus in it with rise in body temperature and abdominal pain.

Two types of desentry:
1. Bacillary caused by shigella.
2. Amoebic caused by E. histolytica.

- Now, back to the carrier, he may out of sudden has relapse and suffer from the disease, there are serious complication of the disease:
1) The wall of the large intestine may rupture and cause peritonitis, so the amoeba is considered as the third common cause of death regarding protozoa after malaria and shistosoma.
2) It may reach the blood stream and then reach the liver through portal circulation and cause liver abscess (mass in the right hypochordorium) with fever and eosinophilia.
- Now it became luminal and tissue parasite, so E. histolytica is both.
- Liver abscess if not treated can be fatal.

Again and again:
- Carrier may has the disease (desentry) or free of symptoms for the rest of his life, but the problem is t hat he is a source of infection excrete cysts with feces all the time, or he may has some MILD symptoms like tendemess and abdominal pain.

How to diagnose it:
- Through examination of feces: you look for either Trophozoite or the cyst, because Trophozoite exist in a large number in the stool (diarrhea) but it is better to search for cysts because it will be always present irrespective to the presence of diarrhea or not. So the cyst is the best means of diagnosis.
- Now, if you look for Trophozoite you have to examine fresh liquid stool.

2) Giardia lamblia:
- Very common protozoa specially in children, live in small intestine.
- If look at the organism, its oval in shape, moves by means of flagella, 4 in each side, has 2 nuclei situated in the middle with very prominent nucleoli.
- Very characteristic owl eye appearance, some say it resembles kite.
- Cyst contain 4 nuclei and flagella are inside and covered by protective layer.
- Cyst excreted with feces, so it contaminates food, and if eaten by someone it travels to the small intestine, and then Trophozoite appears.
- Feco-oral transmission.
- Causes diarrhea: watery and some times can resemble that of steatorrhea. Like what happens with malabsorption.
- These organisms stick them selves to the villi of intestine by sucker and if they are in a large number they cause destruction of the brush border (microvilli) by mechanical or chemical means (its really unknown). Some say that it produces toxins and others say it destruct the brush border by the effect of sucking, so malabsorption happens.

How to diagnose it:
- By examining feces.
- Again, remember that it affects children more, so they suffer from diarrhea and don’t grow normally.

3) Trichomonas vaginalis:
- It has 4 anterior and 1 posterior flagella, and on both sides an adulating membrane, its very mobile and rapid, so, if you examine it under microscope it will be moving every where.
- It’s a luminal parasites in the vagina if the conditions are not healthy, but in normal healthy vagina (low pH) these organisms are killed.
- It produces infections (vaginalis) that cause frothy yellow discharge.
- In males, it can cause disease in urethra usually its not symptomatic but it could be if it is infected the prostate and epididimes.
- Transmission: sexually (mainly affect females), but not always it may be transmitted by mechanical means (towels, etc …) unlike gonorrhea, syphilis, these 2 organisms are always sexually transmitted.
- Trichomonas vaginalis don’t have cysts, because the mean of transmission is very very direct and doesn’t have to live out side, and because it is resistant.
- Examination: vaginal or urethral discharge you look for these very motile trichomonas.

4) Botulinum coli:
- Botulinum means like a sac, coli means live in large intestine.
- Belongs to ciliates.
- Very large protozoa, 80 µm.
- Covered by cilia, so it moves very quickly.
- With 2 nuclei:
a. Mega (macro) nucleus that controls the function of the organism.
b. Mini (micro) nucleus for division of the organism.
- Have two openings:
a. Anterior opening called cytostome.
b. Posterior opening called cytopyge.
So, it feeds through the cytostome, and excrete through cyytopyge.
- Live in large intestine and produce diarrhea which is similar to that of desentry.
- Can be present in animals, specially hogs that may form a reservoir for the infection (not intermediate host).
- You have to differentiate between reservoir and intermediate host or vector:
1. Reservoir: organisms can exist in animals not only in humans.
2. Intermediate host: the organism must be transmitted through it to infect other.
- So, Botulinum coli is a zoorotic organism (can be present in animals).





The End

Done by: Muna Sawwan
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Shadi Jarrar
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عدد المساهمات : 997
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تاريخ التسجيل : 2009-08-28
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الموقع : Amman-Jordan

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