Life Cycle of Entamoeba histolytica

Entamoeba Histolytica

Entamoeba histolytica is a microscopic and endoparasite of human causing a disease known as amoebiasis. It is one of the more serious of the parasitic infections of humans, affecting an estimated 50 million persons worldwide. It is an amoeba, meaning a single cell organism that divides by binary fission and can replicate in the intestinal tract, primarily in the large intestine or colon. In the colon the organisms actually bore their way into the bowel wall, and cause ulcerations, severe bloody diarrhea called dysentery, and abdominal pain.

It is cosmopolitian in distributin (found across the globe). It is abundantly found in the tropical and subtropical region and are mostly common on the place where sanitation is poor.

Morphology

Entamoeba histolytica exists on three forms, namely,

Ø Trophozoite/Magna form (Pathogenic and Active Stage)

Ø Pre-Cystic Stage/ Minuta Stage

Cystic Stage (Infective and resting Stage)

Trophozoite

Pre Cystic Stage

¢ Smaller in size as compared to tropozoite stage.

¢ Encystment occurs by forming cyst wall in intestinal lumen.

¢ Food vacuoles are absent here

¢ Ingested food particles and RBC are seen in endoplasm

Cystic Stage

Ø Dormant/resistant stage

Ø Spherical

Ø 1-4 nuclei, (4 in mature cysts), uninucleate to quadrinucleate (mature cyst)

Ø Bluntly rounded chromatoidal bars

Ø Matured Cyst can sustain 12 days in a cool and moist place and in water 9-30 days

Life Cycle

The life cycle of entamoeba histolytica completes in a single host. viz Man. So it is also called a monogenetic parasites. Human Beings get infecton with this parasite through the consumption of contaminated food and water with quadrinucleate cyst. The gystric juice inside the stomach cannot dissolve the cystic wall due to some kind of resistance on it. As soon as the cyst reaches to the small intestine it will get dissolved through the trypsin enzyme present in duodenal region. From this cyst, now arises a parasite known as metacyst. This process is known as excystation. Now the nucleus of metacyst divides to form eight nucleated metacyst. Finally eight tropozoites will develop from a single metacyst. These tropozoites starts to grow and lodges into the mucosa and submucosa region of large intestine.

Under the commencement of unfavourable condition, a cystic wall starts to develop in each trphozoite. This stage is called Pre-Cystic stage. The single nucleus of the cyst soon undergoes a division to form two and then into four daughter nuclei. This stage of cyst is quadrinucleate. It does not develop further in the large intestine and reaches to outer environment through the faeces. Finally, if these cysts are consumed by next person s/he will get infected again. In this way life cycle of entamoeba histolytica completes in a single host.

Mode of Infection

Ø Oral –faecal type

Ø By ingesting food and water containing quadrinucleate cyst

Ø House fly may act as vector sometimes

Incubation Period- 4-5 days

Pathogenecity

¢ Primary lesions in large intestine at submucosa region

¢ Histolysi, cytolysis, necrosis

¢ Secondary lesion in liver, lungs and brains (Chronical Stage)

Treatment

The choice of drugs are,

Metronidazole, Paramomycin, Diloxanide furoate, Indoquinol, Chloroquine, Schnidazole etc

Prophylaxis (Prevention)

¢ Washing hand with soap and water after toilet

¢ Use toilet

¢ Do not consume under cooked food

¢ Boil water

¢ Wash the vegetables properly

¢ Health Education and awarness

¢ Cover the food stuff.