Parasitology is the scientific discipline concerned with the study of the biology of parasites and parasitic diseases, including the distribution, biochemistry, physiology, molecular biology, ecology, evolution and clinical aspects of parasites, including the host response to these agents.

1. Lec 2
• CLASSIFICATION OF MEDICAL PARASITOLOGY
• Medical Protozoology - Deals with the study of
medically important protozoa.
• Medical Helminthology - Deals with the study of
helminthes (worms) that affect man.
• Medical Entomology - Deals with the study of
arthropods which cause or transmit disease to man.

2. Classification of Medically important
Parasites
The parasite divide into three main groups
Arthropoda(Medical
Entomology) include
Insecta (Butter fly)
Arachnida (Mite)
Crustacea (Cyclops)
Metazoa
Parasite consist of
multicellular cells,
Bilaterally symmetrical
animals, having well-
differentiated tissues
and complex organ
Protozoa
Parasite consist of a
single celled organism
which is morphologically
and functionally
complete and can
perform all function of
life ,reproduction by
asexual or sexual

3. Taxonomic classification of Protozoa
Species-
examples
Genus-
examples
Class
Phylum
Sub kingdom
E. hstolytica
E.nana
I.butchlii
D.fragilis
Entamoeba
Endolimax
Iodameba
Dientameba
Sarcodina-
(Amoeba)
move by
pseudopodia
Sarcomastig-
ophora
further divided into
Protozoa
G. Lamblia
T.vaginalis
T.brucci
L.donovani
Giardia
Trichmonas
Trypanosoma
Leishmania
Mastigophora
(Flagellates)
move by flagella
P. falciparum
T.gonidi
C.parvum
I.beli
Plasmodium
Toxoplasma
Cryptosporidium
Isospora
Apicomplexa
(Sporozoa)
no organelle of
Locomotion
B. coli
Balantidium
Ciliophora
move by cillia

4. Amebas: Move by extending cytoplasmic projections
(pseudopodia)
Ciliates: Move by synchronous beating of hair- like cilia
Sporozoa:(also called apicomplexa) are obligate,
intracellular parasites. They generally have non motile
adult forms.
Flagellates: Move by rotating whip-like flagella

5.  Protozoa are diverse groups of unicellular, eukaryotic
organisms:
 There are about 45,000 protozoan species; around 8000 are
parasitic, and around 250 species are important to humans.
Many have evolved structural features (organelles) that mimic the
organs of multicellular organisms.
 Reproduction is generally by mitotic binary fission, through in
some protozoal species ,sexual ( meiotic) reproduction with several
variations occurs as well. Protozoal infections are common in
developing tropical and subtropical regions where sanitary
conditions and control of the vectors of transmission are poor .
 However, with increased world travel and immigration, protozoal
diseases are no longer confined to specific geographic locales.

6. • Shape
• There is no one shape or morphology which would include a majority of
the protozoa.
• Shape range from the amorphous and ever changing forms of amoeba,
to relatively rigid forms.
• All protozoa have certain morphologic features, like nucleus,
cytoplasm(endoplasm &ectoplasm)
• Nuclear structure - important in species differentiation.
• Size - helpful in identifying organisms; must have calibrated objectives
on the microscope in order to measure accurately.
• Cytoplasmic inclusions - chromatoid bars; red blood cells; food vacuoles
containing bacteria, yeast, etc.
• Appearance of cytoplasm - smooth & clean or vacuolated.(endoplasm &
ectoplasm)
• Endoplasm : the nucleus consist of moderately dense, finally granular
protoplasm that function in the digestion of ingested food and other
process.
• Ectoplasm : serves for locomotion, for obtaining and ingesting food, and
for respiration and excretion.
• Type of motility - directional or non-directional; sluggish or fast.

7. Nuclear Structure:
• Chromatin - nuclear DNA. Present as “peripheral”
chromatin and the karyosome.
• Karyosome - a small mass of chromatin within nuclear
space. Also called “endosome” or “centrosome.”
• Peripheral Chromatin - chromatin adhering to the nuclear
membrane.
• Nuclear membrane - membrane surrounding all nuclear
material.
Feeding
• Protozoa may absorb food via their cell membranes
• Amoebae & other intestinal forms surround food and
engulf it into food vacuoles.
• Others Like Balantidium have opening or mouth pores
they sweep foods into food vacuoles and contractile
vacuoles

8. • Protozoa Reproduction
• A sexual Binary fission
Multiple Fission
• Sexual Fusion of gametes
Conjugation
Some Protozoa use a combination, of sexual and asexual reproduction
• Protozoa Motility
• Mechanism : Flagella , Cilia, Ameboid motility and Gliding motility
• Protozoa generally have two Stage:
• Trophozoite - the motile vegetative ,quite stage; multiply via binary
fission; colonizes host.
• Cyst - the inactive, non-motile, infective stage; survives the
environment due to the presence of a cyst wall. Cysts do not multiply,
however, some organisms divide within the cyst wall.

9. IMPORTANT PROTOZOA
Amebas are unicellular organism belong to the: Sarcodina, common
in the environment, found different species of amoebae naturally
parasitize the human mouth and intestines.
They are three groups of Amoeba
Free Living
Neagleria fowleria
Nonpathogenic ;-
Entamoeba coli
E.gingivalis
Endolimax nana
Iodameba butschili
Pathogenic :-
Entamoeba histolytica

10. • Entamoeba histolytica
• Disease : Amoebiases
• E. histolytica associated with intestinal & extra
intestinal infection.
• E. histolytica inhabits large intestine.
• The other Species are important because the
may be confused with E. histolytica
• They are transmitted by Feco-orally route.
• It occurs in three stages:
• Trophozoite, precyst and cyst
3/27/2023

11. Trophozoite :-
Viable trophozoites vary in size from
about 12-60μm in diameter.
Motility is rapid, progressive, and
unidirectional, through pseudopods.
The nucleus is characterized by
evenly arranged chromatin on the
nuclear membrane and the presence
of centrally located karyosome.
The cytoplasm is usually described as
finely granular with few ingested
bacteria or debris in vacuoles.
In the case of dysentery, however,
RBCs may be visible in the cytoplasm,
and this feature is diagnostic for
E.histolytica.
Lecture One
11

12. • Pre cyst
• It is colourless, Round or oval, Range between
10 – 20 μm in size smaller than Trophozoite &
larger Than Cyst, Sluggish movement, No RBCs
3/27/2023
Lecture two

13. Cyst : (infective stage)
• Found in the lumen of large
intestine.
• Cysts range in size from 10-
20μm. contains four nuclei
when mature, has inclusions
namely; glycogen
• As the cyst matures, the
glycogen completely
disappears.
• The structure of the nucleus is
same as of trophozoite.
3/27/2023
Lecture two

14. Lab.Three

15. Life cycle:

It passes its life cycle in only one host. Man acquires the
infection by ingestion of water and food contaminated with
mature cysts( infective dose usually 1000 cysts ).Infection
may be acquired by anal-oral sexual practices among male
homosexuals. In the small intestine the cyst wall is lysed by
trypsin and a single tetranucleate amoeba is liberated. Each
nucleus divides by binary fission giving rise to eight nuclei,
thus from each mature cyst eight small amoebulae

( Metacystic trophozoites)are produced. This process is
known as excystation . Metacystic trophozoites are carried in
the faecal stream into the caecum. They invade the mucosa
and ultimately lodge in the sub mucous tissue of large
intestine
.


16. Life cycle:

During growth, E. histolytica secretes a proteolytic enzyme of the
nature of histolysin which brings about destruction and necrosis of
tissue and produces flask-shaped ulcers. The amoebae are mostly
present at the periphery of the lesion .At this stage, a large
numberof trophozoites are excreted alone with blood and mucus
in the stool leading to amoebic dysentery. In a few cases, erosion of
the large intestine may be so extensive that trophozoites gian
entrance into the radicles of portal vein and are carried away to
the
liver where they multiply leading to amoebic hepatitis and
amoebic liver abscess.

The trophpzoites , in the lumen of the large intestine, discharge
undigested food particles and transform into precysts and then
into mature cyst . These are the infective forms of the parasite
.This process is Known as encystation.
Lab.Three

17. • Encystation
• Trophozoite round up
• Secretion of cyst wall
• Aggregation of ribosomes (Chromatoid Bodies)
• Two round of nuclear division(1 4) nuclei
• Excystation
• Occurs in small intestine
• Cyst wall disruption
• Nuclear division (4 8)
• Cytoplasmic divisions (8 amebula)
• Trophozoite Migrate to large intestine.
3/27/2023
Lecture two

18. Pathogenesis
 E. histolytica causes intestinal and extraintestinal amoebiasis .
 Infection with E. histolytica may be totally a symptomatic
(90%) or life threatening event.
 E. histolytica, although not strictly an apportunistic pathogen
in that it can cause disease in immunocompetent individuals,
is more common in patients with HIV infection.
 Amoebiasis tends to be more sever in pregnant and lactating
mothers , and in children especially in neonats.

19. Pathogenesis
Some of the mechanisms that have been proposed for causation
of disease are:
-Secretory enzyme : trypsin, pepsin, amylase and hyaluronidase
have been isolated from trophozoite , which resulting tissue
destruction.
-Soluble or trophozoite –free products: these are called as
enterotoxins or cytotoxine , their role in mediating damage to
the tissue.
-Contact-dependent cytolysis: E. histolytica can also cause tissue
injury by direct contact with target cells, lectin mediated
adherence of trophozoite, amebapore forming large
membrane holes. Cytolysis, which appears to require both
intact microfilament function and amoebic phospholipase.
The lysis of neutrophils, which are attracted to trophozoites,
may amplify tissue damage. Dissolution of the extracellular
matrix by cysteine proteases
.

20. -
Other factor influencing pathogenesis
Strain variation
Role of bacteria
Infective dose
Nutritional status
Associated disease
Pregnancy
Drugs
Immunity
Intestinal mucus
Dietary iron

-

21. Pathogenesis
• Non invasive (asymptomatic)
• Caused by E. dispar, less Frequently by E.hisolytica
• E. dispar adheres to cell in vary much the same as E. histolytica.
• asymptomatic cyst passer
• Non-dysentric diarrhea, abdominal cramp, other GI symptoms
 Invasive (symptomatic) E. histolytica
• Necrosis of mucosa ulcer, dysentery
• Ulcer enlargement severe dysentery, colitis, peritonitis
• Metastasis extraintestinal amoebiases.
A- liver amoebiasis
B-Pulmonary amoebiasis
C- cerabral amoebiasis
D- other extraintestinal foci
3/27/2023
Lecture two

22. 
 Intestinal amoebiasis
 Develop early as two to four weeks after infection with E.
histolytica or after asymptomatic periods of months or even
years.
• the amoebae invade the colonic mucosa, producing
characteristic ulcerative lesions and a profuse bloody diarrhea
(amoebic dysentery). the ulcers may be generalized involving
the whole length of the large intestine or may be localized in
the ileo-caecal or sigmoido-rectal region .
• . The size vary from pin-head size to more than 2.5 cm in
diameter .They may be deep or superficial.
• Abdominal discomfort and episodes of diarrhea of varying duration
including blood-mixed.
• Dysentery which ameba can detected, including Trophozoite
containing RBCs
• Fever ,dehydration and toxemia can also present
• In this cases ,antibodies are usually present in serum.


23. 
 E. histolytica may also cause appendicitis and amoebomas.
The latter are pseudotumoural lesions, whose formation is
associated with necrosis, inflammation and oedema of the
mucosa and submucosa of the colon. Amoebomas are
generally single, but occasionally multiple.

 The condition is usually acute with dysentery, abdominal
pain and a palpable mass in the corresponding area of the
abdomen.
 .

24. • Extra intestinal amoebiasis

About 5% individuals with intestinal amoebiasis, 1-3 months
after the disappearance of the dysentric attack, develop hepatic
amoebiasis. E. histolytica are carried as emboli by the radicles of
the portal vein from the base of the ulcer in the large intestine.
They multiply in the liver and lead to cytolytic action. The
amoebae cause obstruction of the portal venules resulting in
anaemic necrosis of hepatic cells.

Amoebic liver abscess varies in size. It may occur in any part
of the liver. Atypical liver abscess include an acute illness with
fever, right upper abdominal tenderness and pain, or sub acutely
with prominent weight loss, fever and abdominal pain.
Laboratory abnormalities include leukocytosis and an elevated
alkaline phosphatase level. .
 Pus of the Liver abscess:
The center of an amoebic liver abscess contains a viscous red-
brown or grey-yellow fluid consisting of cytolysed liver cells ,
red blood cells and leucocytes. It is referred as pus but contains
very few pus cells .

25.  Complications of amoebic liver abscess
 With the continued lysis of liver tissue, the abscess may grow in
various directions coming in contact with neighbouring organs
through which its contents may be discharged .
 A right-sided liver abscess may rupture externally .In such cases
amoebae may cause infection of the skin leading to granuloma
cutis.
 It may rupture into the lungs and pus containing the trophozoites
may be expectorated . It may also rupture into right pleural cavity
leading to empyema thoracis ,below the diaphragm causing
subphrenic abscess and into the peritoneal cavity producing
generalized peritonitis.

26.  A left-sided liver abscess may rupture into the
stomach leading to haematemesis and in the
pericardial cavity leading to pericarditis .
 From the liver, E. histolytica may inter into
general circulation involving lungs, brain,
spleen, skin,etc

27. • Pulmonry Amoebiasis
• Primary:- rare condition even without hepatic amoebiasis,
trophozoite can reach the pulmonary capillaries, via the portal
circulation.
• Secondary :- arise as a complication of liver abscess from the
liver to the base of right lung, resulting in pneumonia.
Cerebral amoebiasis
• is single and of small size located mostly in one of the cerebral
hemisphere.
• Splenic amoebiasis
• Found in association with hepatic abscess
• Cutaneous amoebiasis
• May develop when the skin is in prolonged contact with
amoeba from any cause, such as liver abscess, or colostomy
wound in the site of ruptured appendicular and peri-colic
abscess.
• Mucosa bathed in fluids contain Trophozoite
• Perianal ulcers

28. Epidemiology
1-The infection is due to transmission of mature
cysts with contaminated foods (Fruit,
Vegetables), drinking water or fecally
contaminated hands of infected persons or
carriers.
2-A symptomatic patient are important in the
transmission of the disease.
3-contamination of water is prime source of
infection in many areas.
4- flies and cockroaches can function as
mechanical transmitters by carrying cysts from
the feces to foods. 3/27/2023
Lecture two

29. 5- E.histolytica has a worldwide
distribution. Although it is found in cold
areas, the incidence is highest in tropical
and subtropical regions that have poor
sanitation and contaminated water
6-Super chlorination or addition of iodine
to drinking water are insufficient to kill
cyst.
7-More common un children over 5 years
and in adult males rather than females.
3/27/2023
Lecture two

30. Lecture two
Diagnosis
In intestinal amoebiasis:
•
Examination of a fresh dysenteric faecal specimen or
rectal scraping for trophozoite stage. (Motile amoebae
containing red cells are diagnostic of amoebic
dysentery).
• Examination of formed or semiformed faeces for
cyst stage. (Cysts indicate infection with either a
pathogenic E.histolytica or non-pathogenic E.dispar.)
3/27/2023

31. Extraintestinal amoebiasis
• Hepatic amoebiasis : based on aspirate & liver biopsy to
identify trophozoite.
• Pulmonary ; based on identify trophzoites in sputum
sample.
• Serlogical tests :
• IHA,IFAT
• ELISA,PCR (distinguishes E.histolytica from E. dispar).

32. Treatment
• Treatment of amoebiasis is based on the use of
amoebicides and replacement of fluid, electrolytes
and blood.
• Amoebicides with luminalaction:
Diiodohydroxyquin,Diloxanide furoate, Paromomycin.
• Amoebicides effective in the liver, intestinal wall and
other tissues: Emetine, Dehydroemetine.
• Amoebicides effective only in the liver : Chloroquine
• Amoebicides effective in both the tissue and the
intestinal lumen: Metronidazole, nitroinidazole.
3/27/2023
Lecture two

33. Prevention:
• - Avoiding faecal contamination of food and water.
• - There should be proper disposal of human faces through proper
drainage system. Contamination may result from discharge of sewage into
rivers.
• - Purified water should be distributed through pipelines to avoid
contamination.
• - Boiled water is safe, the amount of chlorine normally used to purify
water is insufficient to kill cyst.
• - Asymptomatic carriers passing large numbers of cysts in their stools
are important source of infection, they should be removed from food-
handing occupations and treated properly.
• - Using human excreta as fertilizer may lead to contamination of
vegetables .Vegetables that are usually eaten raw should be cleaned with
uncontaminated running water and treated with 5% acetic acid before
consuming .
• - Houseflies and cockroaches ingest cysts and can pass them after
periods as long as 24 hours .They can also carry cysts mechanically on their
body .therefore, food exposed to flies and cockroaches should not be
consumed .
• For symptomatic intestinal disease, or extra intestinal infections, the drugs
of choice are metronidazole.

34. Control
• Personal hygiene
• Group hygiene
• Protection of water supply from being contaminated
with feces
3/27/2023
Lecture two