For undergraduate students. it will help them to get prepared for the university exams as well as for the NET/SET.

1. ENTAMOEBA
HISTOLYTICA
BY : Hukam Chand
AP ZOOLOGY
GC DRANG AT NARLA

2. Entamoeba histolytica- The Intestinal Amoeba
GEOGRAPHICAL DISTRIBUTION
It has universal distribution; found in tropical, subtropical, temperate and even in
arctic and antarctic regions. Incidences of infection are high in China, India, Mexico
and parts of South America.
HABITAT
E. Histolytica inhabits the large intestine and lower part of small intestine of
humans worldwide.
HABIT
• It creeps in an amoeboid manner with single pseudopodium (lobopodium).
• Nutrition is chiefly holotrophic.
• The parasite secretes a proteolytic enzyme, cytolysin, which injures the intestinal
mucosa and liberates blood. It takes RBCs, WBCs and broken cells.
• It is a microaerobe (needs little oxygen).
• It reproduces by binary and multiple fissions.
• It forms cysts, which escape with host’s faeces. Human infection occurs by taking
food and water contaminated with cysts.

3. MORPHOLOGY
• Its active form is known as
trophozoite.
• Trophozoite is an irregular, slightly
greyish, about 18-25 μm long.
• Its form changes as it moves. Body is
covered by plasma membrane.
Cytoplasm is divided into outer
ectoplasm and inner endoplasm.
• Endoplasm contains single nucleus.
Nucleus has delicate nuclear
membrane, a small karyosome at the
centre and chromatin granules on
inner surface of nuclear membrane.
• Mouth, cytopyge and contractile
vacuole are absent.

4. LIFE HISTORY
• Certain trophozoites from time to
time prepare for encystation.
• In this process, they become
spherical, smaller and sluggish,
glycogen granules are accumulated
, and 2-3 chromatoidal bodies
begin to appear. Now trophozoites
are known as precystic forms.
• The parasites now secrete a
delicate, shining, colourless,
transparent wall around them and
become cysts. Cysts are spherical
and pass out with the faeces of the
host. During this process the
nucleus of the cyst undergoes two
divisions so that when the cysts
reach outside world they are
tetranucleate.
• Infective stage- Tetranucleate cyst
(four nuclei and chromatoidal
bodies.

5. •The cysts of E. histolytica are highly resistant to
desiccation, temperature and chemicals.
•They remain viable in soil and water for several
weeks to month. The cysts are the infective
forms.
Transmission:
•They may enter into new host in faecally
contaminated food and drinks. Contamination
may occur by settling of cysts from the air or be
brought about by houseflies and cockroaches.
These insects act merely as mechanical vectors.
•Hands of food handlers can also contaminate
food.
•Where human excrement is used as a manure,
is often a source of food and water
contamination. Person to person contact can
also transmit cysts.
•The cysts pass through the gut , resisting the
gastric acidty and reach the ileum, where
excystation occurs. Upon rupture of the cyst
wall a single tetranucleate oraganism comes
out.
•Tetranucleate organism divide once and
produce eight small uninucleate individuals
called metacystic forms.
•The metacystic forms pass into the large
intestine and become trophozoites. The latter
mature in due course.
Life history of E. histolytica.

6. PATHOGENICITY
• It causes amoebic dysentery or
entamoebiasis and abscess formation in
liver, lungs and brain.
• Amoebic dysentery- The proteolytic
enzyme cytolysin damages the mucosa of
intestine, which leads to bleeding ulcers
that cause dysentery. Patient passes out
blood with mucus in stools and
experiences severe gripping pain in
abdomen, fever, nausea, exhaustion and
nervousness.
• Abscess formation- The parasites that
invade intestinal mucosa may be carried
by bloodstream to the liver, lungs and
brain. There it feeds on cells and cause
severe lesions and abscesses, which may
cause death
Diagrammatic representation

7. CONTROL MEASURES
• General cleanliness
and washing of hands
with soap and water
before handling food.
• Washing of the
vegetables and fruits
before taking.
• Protection of foods
and drinks from flies
and cockroaches by
keeping them
covered.