This document provides information about parasites and parasitology. It discusses different types of parasites like protozoa, helminthes, and examples. It then focuses on Entamoeba histolytica, describing its life cycle, morphology, geographical distribution, pathogenesis, clinical presentation, diagnosis, treatment and epidemiology. Key points are that E. histolytica is a protozoan parasite that causes amoebic dysentery. It exists in trophozoite and cyst forms and is transmitted when cysts from infected feces contaminate food or water. The parasite infects the large intestine where it can cause intestinal lesions or spread to other organs.

1. PARASITOLOGY
Mr. Visanth V S
Asso. Professor
IGSCON, Amethi

2. Parasite
• A parasite is a living organism which
depends on a living organism for its survival
and derives nutrition from the host, without
giving any benefit to the host

3. Host
• Definite Host: It is the host that harbors the adult
stage of the parasite or where the parasite
replicate sexually.
• Intermediate Host: It is the host that harbors the
larval stages of the parasite or where the parasite
replicate asexually.
• Reservoir : It is the host that harbors the parasite
and acts as an important source of action.

4. Classification of Parasites
Sl No Class Examples
1.Protozoa (Unicellular)
a. Rhizopoda Entamoeba histolytica
b. Mastigophora
(flagellates)
Giardia lamblia
Trichomonas vaginalis
Leishmania donovani
Trypanosoma
c. Sporozoa Plasmodium
Toxoplasma
d. Ciliates oBalantidium coli
2.Helminthes

5. PROTOZOA

6. Protozoa
Protozoa are subdivided into four groups
Rhizopoda
Mastigophora
Sporozoa
Ciliates

7. Entamoeba histolytica
A typical amoeba; moves by pseudopod
extension.

8. Geographical Distribution
E.histolytica has been found in all
populations through out the world.
It is more prevalent in tropics and subtropics
than the cooler climates.
Habitats
Trophozoites of E.histolytica lives in
mucous and submucous layers of large
intestine

9. Morphology
E. histolytica exists in three forms;
Active trophozoites
Inactive cyst
Intermediate precyst

10. Trophozoites
10-60 X 15-30 m average (15-30 m)
Movement results from long finger like pseudopodial extension of
ectoplasm into which the endoplasm flows.
Cytoplasm is clearly differentiated into:
Ectoplasm: is clear with well developed pseudopodia.
Endoplasm: dense & fine granular enclosing:
Nucleus: spherical and 4m containing central karyosome &
peripheral evenly distributed small chromatin dots.
Food vacuoles: contain leucocytes-bacteria-may be RBCs.

11. Precyst
• 10-20 m
• Round or oval with a blunt pseudopodia.
• Absent cyst wall
• Single nucleus present and endoplasm free from RBC.
Cyst
• Round and 10-20 m average (15 m).
• It is surrounded by a highly refractile mebrane called cyst
wall.
• Nuclear structure is similar to that of trophozoite.
• Four nuclei are present in mature quadrinucleated cyst.
• Glycogen mass & chromatoid bodies are present in
immature cysts –disappear in mature ones.

12. Cyst

13. Life Cycle

14. Cysts are formed in bowel
L
I
F
E
C
Y
C
L
E
Cysts passed with stools
Ingestion of food & water
contaminated with cyst
Cyst reaches intestine
Cyst wall weakened by alkaline
pH
Excystation occurs , 4 nuclei comes out
Binary fission occurs , 8 trophozoites
are formed
They move towards ileocecal region

15. Life cycle of
E. histolytica

17. Life Cycle of Entamoeba inside human colon
Mucosa of large intestine
In the
lumen
Quadrinucleate cyst
Enter with food
Pass out in stool
Precyst Uninucleate cyst Binucleate cyst
Binary fission
Attached
to mucosa
trophozoite
Lumen(non invasive) form

18. Pathogenesis
Depends on:
 Parasite virulence.
 Host resistance.
 Condition of the intestinal tract.
Trophozoites produce histolytic
enzyme that produce necrosis of
mucosa leading to the formation of
flask-shaped ulcer.
Incubation period is 1-4 weeks.
E histolytica produces dysentry.
Intestinal lesions are acute
amoebic dysentry and chronic
intestinal amoebiasis.
Trophozoites exist in the base of
the ulcer

19. This is followed by:
• Proliferation of connective tissue.
• Intensive ulcerations.
• Extra-intestinal invasion to brain,
liver, lung or skin.
Brain
abscess
Liver
abscess
(common)
Lung
abscess
Skin
abscess
Blood vessel

20. Clinical Picture
Asymptomatic: parasite in lumen and cysts pass in stool.
Symptomatic: (gradual onset), fever (low grade), diarrhea, dysentery,
abdominal pain, localized abdominal tenderness, tenesmus &
strain, painful spasm of anal sphincter (indicates rectal ulceration).
Acute intestinal amoebiasis
Recurrent attacks of dysentery with intervening periods of
constipation, abdominal distension & Flatulence, weight loss and
cachexia.
Chronic intestinal amoebiasis.
Rare progressive disease of high mortality (high fever- severe bloody
diarrhea – diffuse tenderness – peritonitis)
Extra-intestinal amoebiasis
Amoebic hepatitis or amoebic abscess, lung abscess, brain
abscess or skin abscess.

21. Complications
• Amoeboma.
(localized granulomatous mass misdiagnosed
with carcinoma)
• Hemorrhage.
• Perforation of ulcer.
(secondary peritonitis --- rare but fatal)
• Stricture of colon.
(secondary to fibrosis)
• Appendicitis.

22. Laboratory Diagnosis
1. Stool Examination: Trophozoites are found in diarrheic
stool. Cysts are found in formed stool.
- Wet preparation.
- Iodine stained.
- Permanent stain with iron haematoxylin or
trichrome.
– Concentration techniques for cysts.
2. Culture Studies
3. Serological tests
4. Proctosigmoidoscopy
5. Liver biopsy

23. Treatment
 Metronidazole
 Chloroquine
 Tinidazole
 Dialoxanide furoate
 Emetine
 Secnidazole

24. Epidemiology
• Cyst passers are the main source of infection.
• Cysts remain viable in faeces for few days, in water for
longer periods.
• Cysts are killed by dryness, heat (over 55ºC) and by
chlorine.
Control
 Treatment of patients.
 Examination and treatment of food handlers.
 Environmental sanitation.
 Personal prophylaxis.
Human faeces should not be used as fertilizers.

25. Difference Between Bacillary & Amoebic Dysentry
Bacillary Amoebic
Frequency 10/day 6-8/day
Amount of stool small More
Consists of blood, mucus but hardly fecal
matter
Feces mixed with blood and mucus
Bright red color Dark red
Viscid mucus adherent to container Liquid or formed mucus
Odorless Offensive
Alkaline Acidic
Pus cells numerous Less in number
RBC lies discretely In clumbs
Charcot Leyden crystals absent Present
E.histolytica absent Present
Bacteria present absent