PHYLUM : Protozoa
SUB PHYLUM : Sarcomastigophora
CLASS : Rhyzopodea
ORDER : Lobosa
FAMILY : Amoebidae
GENUS : Entamoeba
SPECIES : histolytica
1.Entamoeba histolytica is a histozoic, pathogenic and monogenetic parasite invading the mucosal and submucosal layers of the large intestine in man.
2.The infection of the parasite generally causes diarrhea, dysentery and liver abscesses in man.
3.The parasite occurs distributed all over the world.However,it is very common in tropical and subtropical countries than temperate regions. It occurs in the areas of dense human population where food and water are contaminated with human night soil.
4.Entamoeba histolytica spreads through faeco-oral route by unhygienic habits like biting of nails, not washing hands properly before taking food etc.,
5.The parasite was discovered by Lambl in1859.
6.The pathogenic nature of the parasite was reported by Losch in 1875.
7.The name Entamoeba was proposed by Cossagrandi and Barbagallow in 1895.
8.The pathogenic and non-pathogenic stages of Entamoeba are recognized by Schanotunn in 1903.
The life cycle of Entamoeba histolytica , includes three stages ,
2.Precystic stage and
3. Cystic stage.
A. Trophozoite is the motile, feeding and pathogenic stage of E. histolytica.
B. It measures about 20-30 microns in diameter.
C. Trophozoite is surrounded by the limiting membrane called plamalemma.
D. The cytoplasm can be divided into two regions, namely the peripheral ectoplasm and central endoplasm.
E. The ectoplasm is homogeneous, non granular , translucent and the endoplasm is heterogeneous, granular and opaque.
F. Endoplasm contains a number of cell organelles like nucleus , ribosomes and food vacuoles .
G. The nucleus is spherical and vesicular. It measures 4-6 micrometers in diameter .It appears cartwheel like with
1. Peripherally arranged chromatin beeds ,
2. Centrally located endosome and
3. Radiating fine filaments of nucleoplasm.
Having cartwheel like nucleus is the diagnostic character of E. histolytica.
H. Since , the parasite feeds on tissue contents including blood, the food vacuoles are filled by RBCs , which is another distinguishing feature of E. histolytica.
I. Ribosomes occur freely distributed in the cytoplasm and endoplasmic reticulum is absent.
J. Other cell organelles like contractile vacuoles, golgi complex and mitochondria are absent indicating te anaerobic nature of the parasite.
K. It is monopodial and moves always in a straight line with the help of a blunt pseudopodium.
L. It reproduces asexually by binary fission in the wall of large intestine of man.
M. It invades the intestinal tissue by releasing the histozoic enzyme histolysin.
Some of the daughter amoebae that are entered into the lumen of intestine develop transform into precystic stage.
A. It is the nonmotile , nonfeeding and nonpathogenic stage of E. histolytica.
B. It is relatively smaller in size , measuring about 10-20 micrometers.
C. It is almost round in shape with a blunt pseudopodium that does not help in locomotion.
D. The nucleus is relatively larger and cart wheel like.
E. The cytoplasm does not contain RBC and food particles. It contains reserve food in the form of glycogen granules and chromatoid bars ( made of ribonucleo protein ).
A. It is found in the lumen of the large intestine .
B. It is round in shape and is surrounded by a thin , delicate and highly resistant wall.
C. The precess of development of cyst wall is called encystation which is a means to tide over the unfavourable conditions that the parasite is going to encounter while that the parasite is going to encounter while passing to a new host.
C. Soon after the encystations , the nucleus undergoes two successive mitotic divisions to form four daughter nuclei.
D. The cystic stage with four nuclei is called tetranucleate cyst or mature cyst which is the infective stage to man.
LIFE CYCLE OF ENTAMOEBA HISTOLYTICA
1. The life cycle of Entamoeba histolytica , includes three stages , namely
a. Trophozoite stage,
b. Precystic stage and
d. Cystic stage.
2. The adult stages of Entamoeba are called trophozoites. These are the motile, feeding and pathogenic forms.
3. The trophozoites undergo binary fissions in the wall of the large intestine and produce a number of daughter amoebae.
4. They feed upon the bacteria and the host’s tissue elements, grow in size and again multiply.
5. Here, the precystic stages transform into cystic stages by getting cyst wall around itself. Which inturn develop into tetranucleate cysts after the nuclear divisions.
6. These tetranucleate cysts come out along with the faecal matter and can remain alive for about 10 days.
7. These cysts reach new human host through contaminated food and water.
8. They pass into the small intestine of a new human host where the cyst wall gets ruptured by the action of the trypsin, reieasing the tetranucleate amoebae. Such tetranucleate excystic amoebae are called metacysts.
9. The four nucliei of metacyst undergo mitotic divisions and produce eight nuclei. Each nucleus gets a bit of the cytoplasm and thus eight daughter entamoebae or metacystic trophozoites are produced.
10. These young ones devlop into feeding stages called trophozoites. They invade the mucous membrane of the large intestine and grow into mature trophozoites.
2. These ulcers contain cellular debris , lymphocytes, blood corpuscles and bacteria. It leads to the formation of abscesses in rhe wall of large intestine. Ultimately it results in stool with blood and mucous.This condition is called amoebic dysentery or intestinal amoebiasis or tropical amoebiasis.
3. Some people do not exhibit any symptoms. Such pepple are called carriers or asymptomatic cyst passers as their stool contains the tetranucleate cysts. They help in spreading the parasite to other persons.
4. Extra-intestinal amoebiasis
Some times, the trophozoites may rupture the wall of capillaries, enter the blood stream and primarily reach the liver where they mey cause abscesses.From there, they may go to lungs, heart, brain , kidneys, gonads ,etc., and cause abscesses in those parts leading to severe pathological conditions.
The following hygienic habits help prevent spread of this disease;
A. Using boiled and filtered water
B. Washing of hands properly before taking food.
C. Proper washing of vegetables and fruits before using them.
D. Covering of food and drinks. So that they are beyond the reach of house flies, cockroaches etc.,
E. Maintaining personal cleanliness like trimming of nails etc.,
F. Using septic tank toilets.
G. Community prophylaxis includes ;
1. Proper disposal of sewage water.
2. Supply of protected drinking water.
3. Identification and isolation of vectors.
4. Abstaining from eating of snacks from local vendors.
5. Avoiding the use of human night soil as manure.