Animal Diversity (Non Chordates) : Entamoeba histolytica- structure, life cycle, disease, therapy and prevention

 

Introduction

Entamoeba histolytica was first discovered by Lambl in 1859 and its pathological nature was described by a Russian Zoologist ‘Friedrick Losch’ in 1875. He discovered this protozoan in the faeces and intestinal ulcers of a dysentery patient and succeeded in transferring it to puppies.

Classification

Phylum-          Protozoa

Class-              Rhizopoda

Order-             Amoebida

Genus-            Entamoeba

Species-          histolytica  

Distribution

Entamoeba histolytica is cosmopolitan i.e., found everywhere and all most all parts of the world.

Example- Mexico, China, India, South America, Philippines etc.

Particularly it is found in tropical and subtropical areas. It is more common in backward countries, where sanitation is not proper.

Habit and Habitat

Entamoeba histolytica is an endoparasite. It is found in the intestine of man and other vertebrates. It lives in the colon of man.

Enton = within

Amoebae = change

Histos = tissue

Lysis = dissolve  

Entamoeba dissolves intestinal mucosa and feed up on the tissue debris of mucosa. It produces ulcers and secrete pus from intestinal mucosa. It enters in brain, lungs and liver in chronic patients. It produces Amoebic dysentery or Amoebiasis in man.

Infants under a year old are rarely infected with it, while children and young adults are very susceptible to the parasite.

Entamoeba is monogenetic, it found in man, pig, gorilla, dog and buffalo also.

Structure

Entamoeba histolytica is found in three forms according to shape and size.

1.       Trophozoite form or Magna form

2.       Minute form or pre-cystic form

3.       Cystic form

 

1.       Magna form-

This form is large and motile. It is 20-30 micron in size. Due to large size, it is called magna form. It produces disease in man. The cytoplasm of magna form is clearly divisible into ectoplasm and endoplasm. Single pseudopodia is found, hence it is monopodial species.

In the endoplasm, food vacuoles, RBCs and bacteria are found. Contractile vacuole absent. Nucleus is large 4-6 micron in size. Below nuclear membrane chromatic granules are found. In the center, a round endosome or karyosome is present. Around endosome, a clear area is present called Halo.

Nucleoplasm is in the form of striations like spokes of cycle.

It produces disease in man or in vertebrate because it is ficolin form. It feeds on tissue of intestinal mucosa.

 

Entamoeba histolytica: Vesicular nucleus 

2.       Pre-cystic form or minute form-

This form is smaller than magna form. It lives in the cavity of large intestine. It is non-feeding form. It is 15-20 micron in size. It is produced by trophozoite form. Nucleus is familiar to the nucleus of trophozoite form.

 

3.       Cystic form-

Minute form because round and secretes a hard cyst with single nucleus is called monocystic form. Nucleus of monocystic form divides to form two nucleus. It is called binucleated cystic form. The two nucleus of binucleate cystic form divides to form four nucleus, now it is called tetranucleate or quadrinucleate cystic form. One or two glycogen masses found in cyst as reserve food materials. All three forms mononucleate, binucleate and tetranucleate cystic form are present in the cavity of large intestine. These comes out from the faeces of host (man).

 

Entamoeba histolytica: Structure of three stages of life cycle 

 

 

Reproduction and Life Cycle of Entamoeba histolytica

Entamoeba histolytica is mono-genetic because it completed its life cycle in single host (man).

Magna form is found to attached with intestinal mucosa, it feeds and grows. It divides by binary fission. Division is like mitosis. Single entamoeba produces two amoebae. It grows to form again magna form. Some of magna form becomes smaller and form minute form. It do not feed. It lies in the cavity of intestine.

Minute form becomes cystic form because it’s cyst is protecting the parasite from digestive enzymes of the host. All these forms comes out from the faeces of man. Cyst is hard, light and greenish in colour.

On faeces, flies sit and flies carries the cyst to open food and water and vegetables. In this way food and water becomes contaminated and it infect new host (man).

In the tetranucleate cystic stage is ingested through contaminated food and water. It reaches to the stomach but there are no effect of gastric juice on cyst. When cyst reaches to intestine. It ruptures by the action of intestinal juice and tetra nucleate stage comes in the lumen (cavity) of host. This stage is called metacystic stage. Metacystic stage with four nucleus divides and redivides to form eight amoebae. Each becomes large and form magna form. Magna form attaches with the intestinal mucosa. It feeds on mucosal cells or intestinal cells. Sometimes, it rupture the intestinal wall and reaches to blood streams. It may reaches to liver and brain. It produces hepatitis and secondary complications. From the intestinal mucosa blood with mucus comes out and passes through anus along with stool.

Entamoeba histolytica: Reproduction and life history 

Disease

This disease is called blood dysentery. It produces abdominal pain and host appetite. Sometimes produces anemia due to loss of blood. In this way loss of weight is common. Patients want to continued in the lavatory. Frequent intestinal pain takes place.

Diagnosis

In a simple way, the microscopical detection of trophozoites or cysts in faecal smears.

Therapy

Treatment of amoebic dysentery is not very difficult but the permanent cure is sometimes hard to achieve as relapses do occur. For temporary relief, an alkaloid Emetine is effective. A synthetic derivative of Emetine, called Dehydroemetine, is equally effective. The antimalaria drug, chloroquine is effective against amoebic abscesses in the liver but not elsewhere. Some of the latest iodine compounds, such as Vioform , Chiniofon, Diodoquin, etc., have shown more lasting results. Certain antibiotics, such as Fumagillin, Terramycin, Erythromycin and Aureomycin have proved to be effective in the eradication of the parasite.

Prevention

It is the matter of personal as well as municipal hygiene.

For personal hygiene, we need to follow following habits-

1.       Protection of food and water from contamination by houseflies, cockroaches, etc.

2.       Cutting finger nails regularly.

3.       Washing hands with soap and water after handling dirty articles, before taking meals and after using toilet.

4.       Avoiding use of unboiled water and improperly washed vegetables and raw salads.

5.       Avoiding passing out of stool on open grounds, street sides or vegetables fields.

 

The municipal hygiene is the responsibility of the town areas. They must take the following preventive measures-

1.       Proper disposal of sewage.

2.       Purification of drinking water.

3.       Chemical treatment of human faeces to be used as fertilizer.

4.       Proper sanitation of roads, streets, lanes and open drains.