PARASITOLOGY

DR.ABID HUSSAIN CHANG

Professor
Parasites occur in two distinct
forms:

Protozoa---Unicellular
Metazoa---Multicellular

.Protozoa divided into 4 groups

.Metazoa into 2 groups
Parasitology Classification
Parasite

Host

Definitive host
Intermediate host
Protozoa-Introduction
 Are unicellular & widely distributed in nature
 Basic structure:
Protoplasm differentiated into cytoplasm &
nucleus
A limiting membrane or plasma membrane
which is pliable– some cases
Outer coat is more rigid– Majority of protozoa
 Locomotion, an important characteristic-
three organelles: Flagella, cillia, pseudopodia
Amoeba-Common Terms

Trophozoite: Motile form

Cyst: Non motile.cystwall/membrane.Infective stage in

most

Pre-cyst: Rounded form of Trophozoite preceeding

cystic stage

Excystation: Process of emergence of

trophozoite from the cyst

Encystation: Process of formation of cyst

from trophozoite
Amoeba- classification
1-Pathogenic intestinal amoeba:
Entamoeba histolytica
Endolimax nana
2-Non pathogenic intestinal amoeba:
Entamoeba hartmanni
Entamoeba coli
Iodamoeba butschlii
3-Free living amoeba:
Naeggleria spp
Acanthamoeba spp
Intestinal and
Urogenital
Protozoa
 Enatamoeba histolytica
(Amoebic Dysentery & Liver abscess)
 Two stages in life cycle:

.Trophozoite– Motile
.Cyst– ----------Non motile
.Trophozoite is found in intestinal & extra
intestinal lesions & in diarrheal stools.
.Cyst .Manly found in non diarrheal stool
.Not highly resistant and
readily killed by boiling, also removed by
filtration but,
not by chlorination
Cyst- four nuclei- diagnostic

V/S other amoeba

Excystation
in GIT– Amoeba with four
nuclei-divides–).
These enter large intestine & may:
1-invade host tissues 2- live in
lumen of colon without infection 3-
Encyst

Only Cysts can survive in external

environment for any length of time

Antibodies-not protective but

diagnostic
 Pathogenesis & Life cycle
 Infection -------By ingestion of cysts
.Transmission--fecal oral route
.contaminated food & water
Cysts differentiate into
Trophozoites in ileum.
Trophozoites invade colonic
epithelium, secrete proteolytic
enzymes that cause necrosis.
Invasion results in bleeding & RBCs
ingested by trophozoites
Pathogenesis & Life cycle…….
 More deeper invasion till reach
muscularis & submucosa.
.Destroy tissues near and far & necrosis
results.
.Formation of small abscesses, ultimately
result in ulcers
 The Ulcers may be: Shallow erroding
only Mucosa or Deeper entering
Submucosa.
 In S/mucosa: Trophozoites multiply
rapidly & spread laterally forming
Flask shaped ulcer (broad based)
Pathogenesis & Life cycle……
Invasion of submucosa–
invasion of portal circulation
Most frequent systemic disease

site is Liver & Abscesses

form.
(Lungs & brain)
Clinical features
Acute Dysentery + Lower
abdominal discomfort + Flatulence +
Tenesmus
.may last for few days or weeks and
resolves spontaneously or transforms
into chronic disease:
Chronic Diarrhea on & off +Wt.
loss +Fatigue

90% are Asymptomatic carriers

 IntestinalComplications:
.Amoeboma :

A granulomatous lesion resembling

adenocarcinoma colon
can occur in some-
Common sites: Cecum,Recto-
sigmoid

.Hemorrhage
.Appendicitis
.Perforation
Clinical features
Amoebic liver abscess-
.Right upper quadrant abdominal
pain
.Wt. loss, fever, hepatomegally,
.tender abdomen.
.Leukocytosis & raised ESR
.Anchovy sauce- Brownish yellow
pus
Pus is a mixture of sloughed liver
tissue & blood.
Laboratory diagnosis

1-Intestinal Amoebiasis:
.Fecal Examination: for trophozoites &
cysts
Trophozoites are present in Diarrheal
stool
Cysts are present in Formed solid stool
.Charcot-Leyden crystals
.E.histolytica antigen in stool-specific
.PCR detects nucleic acids of organism
Serologic test for invasive disease
Laboratory diagnosis
2-Extraintestinal Amoebiasis:
Cysts or Trophozoites may not be present
in feces -
so valuable are,

Serological tests: (+ve in >90%
cases)
.4 most commonly used:
1.Gel diffusion 2.Indirect hemaglutination
3.Latex agglutination 4. Flourescent antibody
test
also ELISA
Lab diagnosis Extraintestinal Amoebiasis

Aspiration of Liver abscess:

Bacteriologically sterile
.Contains:
. Degenerated liver cells
. Few RBCs
. Occasional leukocytes
. Trophozoites may be present
 Giardia
Giardia lamblia is main
type- Giardiasis
 Two stages in life cycle
Trophozoite Pear shaped
Resembles Badminton racket
two nuclei, flagella (four pairs)
suction disk for attachment to
intestine
Movement: Falling leaf movement
(Rolls on itself)
Cyst, oval, , four nuclei
.thick walled
Pathogenesis

Infection by ingestion of cysts in

fecally contaminated food and water
Excystation occurs in duodenum,
trophozoite attaches to gut. does
not invade mucosa &
does not enter blood stream
.causes inflammation of duodenal
mucosa leading to malabsorption of
protein & fat
 Clinical features

Watery, non bloody diarrhea,foul

smelling
+ nausea, anorexia,
flatullence, abdominal cramps-
No Fever
Laboratory diagnosis

 Examination of Diarrheal stools:

Trophozoites or cysts/both—less
reliable
 Deudenal aspirates-- more reliable

String test
Weighed object connected to string is
swallowed and pulled back when
touches deudenum, attached cont
 ELISA- Detects Giardia antigen
Free living Amoebae

Found in soil and water

Naegleria Fowleri- more
common than
Acanthamoeba castellani
Infection results from swimming
in contaminated water
Amoebae pass through nasal
cavity,
invade cribriform plate and then
 Clinicallycauses *Primary
meningo encephalitis*
 Should be suspected in
individuals with meningo-
encephalitis who have been
swimming in fresh water
pools, ponds 3-7 days
previously
Labdiagnosis:

CSF: Microscopy may reveal

the presence of trophozoites
RBCs
Bacteriologically sterile
Treatment: Nitroimidazoles --
no value
.Amphotericin B – only drug
with efficacy
should be given I/V not orally
.If poor response, administer
 Urogenital Protozoa
 Trichomonas hominis ---
Large intestine
 Trichomonas tenax -----
Mouth
 Trichomonas
vaginalis ---- is main
 Life cycle has only one stage
(Trophozoite)
no cyst stage
 A pear shaped organism with a
central nucleus & 4 anterior
flagella
 5th flagellum turns back &
attached to body by undulating
Pathogenesis
This is only parasite that is
transmitted by sexual contact.
(Man acting as carrier) Then it
resides in vagina & prostate
damaging epithelial cells by
release of cytotoxic chemicals.
Clinical Features:
 Women: Vaginitis:
watery, foul smelling,
greenish vaginal discharge with
itching & burning,
dyspareunia.

 Men: Mostly asymptomatic

10% have urethritis with
burning micturition, Dysuria
and thin, white, urethral
discharge may be present.
Lab diagnosis
Samples:

.Vaginal or prostatic
secretions or semen
.Wet mount film
under microscope
shows pear shaped
trophozoite having
typical
Jerky motion
NAAT: are highly
Blood & Tissue Protozoa

Plasmodium
Toxoplasma
Trypanosoma
Leishmania
Plasmodium
Malarial parasite
Fourtypes of Plasmodia Cause
Malaria:

1- P.vivax (common)
2- P.falciparum (common)
3-P.ovale
4-P.malariae
P.knowlesi---- in Southeast Asia
Vector is female Anopheles mosquito
Life cycle= two phases

1-Sexual cycle occurs in

F.Anopheles mosquitoes
2-Asexual cycle occurs in humans

Other routes of transmission:

Transplacental, Blood transfusion
 Life cycle in Humans-Asexual
(Schizogony)
 Life cycle in Humans: Begins with the introduction of Sporozoites into
the blood from saliva of biting mosquito.
 Sporozoites enter liver cells(30 minutes) & change into Merozoites
(Exo Erythrocytic phase)
 Merozoites are released from liver & infect RBCs (Erythrocytic
phase).
 organism changes into ring shaped Trophozoite, then changes into,
 Schizont filled with many merozoites.
 Life cycle
Merozoites are released, infecting other
RBCs
The RBC cycle repeats at regular
intervals
The periodic release of merozoites
(Typical for each species) causes the
typical recurrent symptoms of chills,
fever & sweats in malaria.

Merozoites
in human RBCs develop into
gametocytes
Life cycle in Mosquito (sporpgony)

These RBCs containing

gametocytes are ingested by
female anopheles mosquito during
bite.
Gemetocytes produce male
Microgamete & female
Macrogametes in its gut,
fertilization occurs,
 Zygote is formed-, changes into,
Life cycle in Mosquito

 Ookinete (motile)
.Penetrates & burrows into gut wall of
mosquito & changes into circular body

 Oocyst whithin which many

sporozoites produce which migrate
to salivary glands & transmitted to
humans when mosquito bites for its
blood meal.
Pathogenesis
Pathologic findings are mainly
due to destruction of RBCs
due to
Release of merozoites &
lysis in spleen-----
Splenomegally
Pathogenesis

P.falciparum Malaria is more

severe than other plasmodia.
 More number of RBCs are
damaged & occlusion of
capillaries with aggregates of
parasitized RBCs
 This can lead to severe life
threatening hemorrhage &
necrosis esp: in brain (Cerebral
malaria)
Pathogenesis
Excessive hemolysis & kidney
damage resulting in
hemoglobinuria. Urine dark
coloured (Black water Fever)
---ARF
P.malariae fever- 72 hours
(Quartan malaria as it recurs
every 4th day) & for 48 hours for
other plamodia (tertiam malria
as it recurs every third day)
Tertian by P.falciparum is called
 Persons who do not produce Duffy blood group antigen (Black
west africans) are resistant to P.vivax because this antigen works
as receptor required for P.vivax
 G6PD deficients are also protected against P.falciparum.
 Patients with sickle cell anemia are resistant to malaria because
their RBCs are defficient in ATPase activity
RBCs don’t produce sufficient energy required for growth of
parasite.
 Clinicalonset
Abrupt features
of fever & chills +
headache+ myalgias +Arthralgias
about 2 wks after mosquito bite.
Fever is continuous in early phase,
and typical periodic cycle is absent.
+++Anemia, Splenomegally &
hepatomegally
P.falciparum causes life
threatening lesions
Cerebral malaria with extensive
brain damage & Black water fever
 Lab Diagnosis
 Examination of
blood (Thick & thin Giemsa
stained smears)

.Trophozoites (within
RBCs)

Ring shaped

.Gametocytes
Banana or
crescent shaped
(P.falciparum)
spherical in others
Toxoplasma
Toxoplasma

Toxoplasma gondii .
 A very common parasite of
human & animals
 Causes Toxoplasmosis
Atleast 1/3rd world population
contracts Toxoplasma

TORCH
Toxoplasma
 Animals involved ---- Range is Wide
 Definitive host is domestic cat &
felines
Humans & other mammals are
intermediate hosts.
 Host immune system limits spread
Cell mediated immunity---Major role
Antibodies also kill it.
Organism persists as cysts within
tissues
Life cycle…
In Cat (Definitive host):
Begins with ingestion of
raw meat (eg.mice)
Bradyzoites released from cysts
in small intestine, penetrate &
infect mucosal cells
1stly: Asexual cycle occurs
---- formation of merozoites-----
enter fresh host cells & initiate
different cycles
Life cycle
Some of Merozoites Transform
into sexual stages- (initiate
gametogony)
.Macrogamate---Fertilized by a
motile Microgamate----Zygote ---
Oocyst formed
Disintegration of host cell epith.
reulting in Oocysts passed in cat
feces.
 Man is infected when
ingests soil contaminated
with oocysts.
 Human infection occurs with
ingestion of cysts in
undercooked meat (Lamb or
pork) from animals that
grazed in soil contaminated
with cat feces

Life cycle- Human (Intermediate host):

Infection: 1-by accidental contact

with Oocysts in cat feces. or
2- eating improperly
cooked meat
(Pork, Mutton ,Beef, Poultry)
containig cysts
.Cysts rupture in small intestine-New
forms ingested by macrophages,form
Tachyzoites (Rapidly multiplying)
.Only Asexual development in
man & no oocysts formed.
.Merozoites enter
lymphatics & blood----

Cysts & Pseudocysts in

various organs (Brain
muscle etc--Bradyzoites –
slowly multiplying)
Pathogenesis..
Routes of transmission :By
Ingestion of Cysts in undercooked
meat or cat feces
Transplacental from mother to
fetus

 Spread: Mainly to Brain , lungs, liver &

eyes
Form Cysts (Endozoites)
 Congenital infection: Can occur only when mother is
infected during pregnancy but not if infected before
pregnancy because no trophozoites to pass through
placenta
Clinical features
Mostare asymptomatic
Congenital : (More severe in
congenital form)
Abortion or Stillbirth or,
Neonatal disease
(Encephalitis,
hydrocephalus, intracranial
calcifications)
+ fever, jaundice,.
Clinical features- (Congenital )
 Less severe lesions as
Chorioretinitis (Pigment ringed scar),
Congenital Toxoplasmosis, leading causes
of blindness in children
Hepatosplenomegally generally
missed at birth may be observed latter in
life.

 Mental retardation in some- months or

years latter.
Clinical features-

Acquired Toxoplasmosis:
less severe form

 May show involvement of Eyes &

Lymphatics
Eyes :
Uveitis, Choroiditis, Choroidoretinitis
Lymphatic system :
Lymphadenopathy with/ without fever

 Rarely-- Myocarditis - Myositis

Clinical features

Toxo. in immunodefficient host:

(Result of reactivation of latent
infection)
.Mild to severe, ending in fatal
acute fulminating disease.

 Necrotizing Encephalitis,
Myocarditis, Pneumonitis (Autopsy
findings)
 Lab diagnosis..
Giemsa staining & microscopy:
Crescent shaped trophozoites
 Isolationor detection of parasite not always
possible/successful
Serological tests to detect
antibodies
.Flourescent antibody test :(a Sensitive
test) For acute & congenital infections (IgM)

Flourescein labelled anti IgM is used for congenital

toxoplasmosis also because IgG may be from mother
Lab diagnosis..

.Dye test of Sabin & Feldman:

.Depends on the cytoplasmic lysis of

endozoites when they are exposed
to the antibody in the presence of a
heat sensitive non specific substance
found in the serum of certain
individuals known as Accessory factor
.Modified parasites appear unstained
or clear when treated with methylene
blue
 .Indirect Haemagglutination
test:
.A very sensitive test but
. D/A is that it takes longer to
become positive compared with
Dye test & FAT.
. Once positive it remains so for
years
TRYPANOSOMA &
 LEISHMANIA

.Also called
Hemoflagellates
Trypanosoma
Three (3) major pathogens:

1- Trypanosoma cruzi- Chaga`s

disease

2- Trypanosoma gambiense
3- Trypanosoma rhodesiense

.Both cause Sleeping sickness

Trypanosoma cruzi
 Causeschaga`s disease (American
Trypanosomiasis)

 LifeCycle: Rueduvid bug is the vector which

transmits organism when bites humans or other
reservoir hosts (Dogs, cats, rats)

In Man:
At the time of bite, the bug releases organisms in
feces, Trypomastigotes (Metacyclic forms), which
are rubbed into bite site & enter blood of person
and penetrate cardiac muscle & change into
Amastigote, Epimastigote & Trypomastigote forms.
 Inside
Bug--- Trypomastigotes ×××
& change to Epimastigotes before
becoming Trypomastigotes which
can be excreted in feces.

Affects many cells as,

Myocardial, Glial &
Reticuloendothelial cells
 Disease occurs mostly in rural areas because the bug resides in rural
huts & feeds at night.
 Preferentially bites arround mouth or eyes hence named also as

kissing bug.
 Produces focal lymohangitis & oedema at bite site--- facial edema &
a nodule (Chagoma)
 Cardiac muscle is severely affected, may result in Congestive heart
failure
 Neuronal cells are also affected which can result in Cardiac Arrythmias
& loss of tone in colon (Megacolon)
Clinical features
 Primary lesion (Chagoma) usually found on face near eyelids
producing swelling of eye & temporal region (Romana`s sign)
+ Fever + Lymphadenopathy +
Hepatosplenomegally
 Cardiomyopathy:
.In Mild, Extrasystole + slight Tachycardia
.In severe cases: Partial or Complete Heart block leading to Cardiac
failure (Cause of death)
 Some cases: Dilatation of esophagus (Mega esophagus) &
Megacolon (Dilatation of colon)
Laboratory diagnosis
 Isolation of T.cruzi from blood:
a) Can be found by direct examination (stained & wet films) but
requires concentration methods as centrifugation so rarely done.
 Bone marrow examination can be alternate.
 Muscle biopsy (Amastigotes)
B) culture , on N.N.N (Novy,McNeal, Nicolle) medium is very
useful
 Xenodiagnosis:

Atleast 6 clean uninfected laboratory

bred reduvid bugs are allowed to feed
on suspected pt. & hindgut of bug
examined after 2 weeks for
epimastigotes

 Serological
methods: are + in
majority cases

.Indirect haemagglutination
.Flourescent antibody test (FAT)
Trypanosoma gambiense &
Trypanosoma rhodesiense

Cause Sleeping sickness

(African Trypanosomiasis)

Vector: Tsetse fly (Glossina):

Which bites & injects organism to
human, where they enter into
bloodstream, undergo different
developmental stages
.Spread to lymph nodes & brain
 Life cycle
In tsetse fly : Bite---Ingests Trypomastigotes from
reservoir host.
.××× in gut and migrate to salivary glands & change to Epimastigotes.
.××× then form metcyclic Trypomastigotes & transmitted by tsetse fly
bite.

In man: From injection site in skin enter bloodstream (Blood

form trypomastigotes) & ××.

Rarely as Amastigotes in
tissue--- v/s T.cruzi &
Leishmania
Pathogenesis & Clinical
features
Spreads from skin to L.N & Brain
through blood.
Sleeping sickness progresses to
coma-- due to demyelinating
encephalitis.
 Skin ulcer occurs at bite site (Trypanosomal chancre)
 Intermittent weekly fever & lymphadenopathy (Organism
enters blood)
 Pathogenesis & Clinical features

Winterbottom sign (Enlargement

of posterior cevical L.N)
Encephalitis characterized by

.headache, insomnia & mood

changes. followed by,
muscle tremors, slurred speech.
.This progresses to somnolence &
coma
.Untreated case can lead to death
Laboratory diagnosis
 Demonstration of parasite:
Blood or aspirate of chancre or L.N
CSF (Trypanosomes)
 Serologic :

ELISA
CFT
FAT
Tr: Suramin - Melarsoprol (In CNS
disease)
Leishmania
4 major pathogens:
.L.donovani (visceral leishmaniasis
)
.L.Tropica---- Both cause cutaneous
.L.mexicana-- leishmaniasis
.L.braziliences--cause muco-
cutaneous
leishmaniasis
Leishmania donovani
Causes kala azar (visceral
leishmaniasis)
Life cycle Vector: Sand fly
(Female) which sucks blood from an
infected host (dogs,foxes, rodents)
and ingests macrophages containing
amastigote stage of organism.
Dissolution of macrophages releases
amastigotes--- change to
promastigotes & multiply.
 Finally migrates to pharynx of sand fly from where they can be transmitted
during next bite

 In humans after bite,

Promastigotes are engulfed by &
survive within macrophages—change
into Amastigotes.
 Infected macrophages die, progeny
organism released which infects other
macrophages & reticuloendothelial
cells.
 They are transmitted to sand fly during
bite.
Pathogenesis

 Organs of reticuloendothelial system

(Liver, spleen & bone marrow) are
severely affected
 Reduced bone marrow activity results in

Anemia, Leukopenia & thrombocytopenia

resulting in
secondary infection & bleeding tendency

Spleenomegally is striking
 Clinical features
 Visceral leishmaniasis: (Kala-azar)

.Intermittent fever, weakness, weight

loss
Massive Splenomegally,
Hyperpigmentation
(kala azar – Black sickness).

Disease runs for months to years.

.

weakness, infection & GIT bleeding

occur. .Death if not treated
Muco cutaneous
leishmaniasis:
Starts as pustular swelling in
mouth or on nostrils
.May become ulcerative after
many months & extends into
nasopharyngeal mucous
membrane.
.2ndary infection very
common-with destruction of
Cutaneous leishmaniasis:
Starts as
.Painless papule on exposed
parts (Face,extremities)

.Ulcerates after few months

(Circular/oval ulcer with
indurated margin)
 Laboratory Diagnosis
 Visceral L: Blood changes are earlier
.Detecting Amastigotes in Stained blood slide, bone marrow
.spleen (by splenic puncture.
. L.N aspirate or biopsy
Culture: N.N.N medium Slow. Takes 1 month
.Serologic: FAT
Indirect immunoflourescence
IgG-

.Formol gel test- A drop of commercial formaldehyde +1 ml pt

serum--- a coagulum.

.Leucopenia Anemia
Lab. Diagnosis Cutaneous & Mucocutaneous
 Consists of microscopical exam. of a smear made from margins of
Sore/ulcer & stained by leishman----Amastigote forms will be found
inside macrophages.
 Cultures : N.N.N medium
 Montengro test: Consists of intradermal injection 0.1 ml of antigen
prepared from cultures of promastigotes---
*Erythema & Induration—48 hours*

TR: Sodium stibogluconate (Antimony compound)