Transcript Slide 1

 PROTOZOA
 Unicellular, eukaryotic organisms of kingdom Protista (3-2000
mm).
 Protozoan means “first animal”.
 20,000 species, only a few are pathogens.
 Most are free-living organisms that inhabit water and soil.
Some live in association with other organisms as parasites or
symbionts.
 Reproduce asexually by fission, budding, or schizogony.
 Some exhibit sexual reproduction (e.g.: Paramecium).
 Trophozoite: Vegetative stage which feeds upon bacteria and
particulate nutrients.
 Cyst: Some protozoa produce a protective capsule under
adverse conditions (toxins, scarce water, food, or oxygen).
 PROTOZOA (Continued)
 Nutrition
 Some ingest whole algae, yeast, bacteria, or smaller
protozoans. Others live on dead and decaying
matter. Parasitic protozoa break down and absorb
nutrients from their hosts.
 Some transport food across the membrane.
 Others have a protective covering (pellicle) and
required specialized structures to take in food.
– Ciliates take in food through a cytostome.
 Digestion takes place in vacuoles.
 Waste may be eliminated through plasma membrane
or an anal pore.
Protozoan classification
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The groups are:
flagellates (or Mastigophora)
amoebae (or Sarcodina)
sporozoans (or Sporozoa, Apicomplexa)
and
• ciliates (or Ciliophora).
Ecological Niches in the
Human Body:
• 1. Skin: Leishmania
• 2. Eye: Acanthamoeba
• 3. Mouth: Amoebae and flagellates
(usually non-pathogenic)
• 4.Gut: Giardia, Entamoeba (and invasion to
liver), Cryptosporidium,
Isospora, Balantidium
• 5. G.U. tract: Trichomonas
Ecological Niches in the
Human Body:
• 6. Bloodstream: Plasmodium,
Trypanosoma
• 7. Spleen: Leishmania
• 8. Liver: Leishmania, Entamoeba
• 9. Muscle: Trypanosoma cruzi
• 10. CNS: Trypanosoma, Naegleria,
Toxoplasma, Plasmodium
INTESTINAL PROTOZOA
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Pathogenic
Entamoeba histolytica
Balantidium coli
Giardia lamblia
Dientamoeba fragilis
Cryptosporidium parvum
Enterocytozoon bieneusi
Septata intestinalis
Cyclospora cayetanensis
Isospora belli
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Commensal
Entamoeba hartmani
Entamoeba dispar
Entamoeba coli
Endolimax nana
Iodamoeba bütschlii
Chilomastix mesnili
Trichomonas hominis
Blastocystis hominis
Entamoeba histolytica
Trophozoites and Cysts
• multiple well defined
pseudopodia often extended
eruptively
• Differentiation into endo- and
ectoplasm
• Spherical nucleus (4-7 mm) with
small central nucleolus and
characteristic radial spokes
Phagocytosis
Trophozoites and Cysts
• Tissue forms often contain
phagocytosed RBCs
• Trophozoites encyst and
cysts mature as they travel
through the colon
• Only mature cysts are
infective
Trophozoites and Cysts
Trophozoites and Cysts
 Round (10- 16 mm), 4 nuclei
 150 nm cyst wall with fibrillar
structure
 Impermeable cyst wall is
responsible for chlorine
restistence
• Chromidial bodies and bars
are semicrystalline arrays of
riobosomes
Entamoeba cysts (light microscopy)
E. coli
E. histolytica
E. histolytica trophozoites and cysts
(Ingested red blood cells)
Right:
E. histolytica
trophozoites
(trichrome stain)
Right:
E. histolytica cysts
iodine (L); trichrome (R)
E. histolytica
pathology/clinical symptoms
• worldwide with infection rates ~50% in endemic
areas such as C. & S. America, Africa, Asia.
• 90% of patients are asymptomatic contributing to
the spread of disease. Long term infection will
result in pathogenesis. Damage may go unnoticed
for some period of time. Trophs are responsible for
all pathology.
• E. histolytica usually is a benign gut commensal as
many other amoebae. A certain stimulus (gut flora,
diet, host immune status …) transforms the
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organism into a pathogen
E. histolytica
pathology/clinical symptoms cont.
Intestinal: may be a single event or
recurrent
a)amoebic colitis: cramps with
alternation between loose stool
and constipation
b)dysentery: infected patients hydrolytic enzymes penetrate
small hole or ulcer in mucosa,
reaches musculature & spreads
laterally causing significant
undercutting = severe pain,
sloughing of mucosa  blood &
mucus in watery stools, “tear
drop” or “flask-like” intestinal
lesions.
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Colitis is the most common form of disease
associated with amoebae
• Amoeba invade mucosa and
erode through laminia propria
causing characterisitic flask
shaped ulcers contained by
muscularis
E. histolytica pathology continued
• extraintestinal: Trophs perforate bowel causing
peritonitis, and travel to other organs:
• liver: crater-shaped abcesses on surface of liver
with chocolate colored exudate.
• Anemia, weight loss & elevated alkaline
phosphatase due to liver damage.
• Abcesses in brain, lung, kidney even more rare
Typical pathology of E. histolytica:
a) flask-shaped abcess in mucosa
b) crater-shaped liver abcess
c) liver abcess damage – tube of
“chocolate puss” from abcess
Ulceration can lead to secondary
infection and extraintestinal lesions
Complications
 amebic liver abscess
 intestinal perforation, peritonitis
 intestinal hemorrhage
 intestinal ameboma
 amebic appendicitis
Amebic liver abscess
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Most common
complication of
extraintestinal amebiasis
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Fast growing abscess filled with debris,
amoebae are found only at borders
Lead symptoms are are right upper
quadrant pain and fever
30-50% of patients with liver abscess
show also pneumonic involvement
Rupture is again a major thread,
especially rupture into pericardium
Draining abscesses is today only
performed in extreme cases when
rupture is feared
Responds well to chemotherapy
Diagnosis:
 stool examination - for trophozoites and
cysts
 amoebic serology
 abscess aspirate
 Antigen capture and PCR tests can
distinguish E. dispar from E. histolytica in
heavier infections.
FLAGELLATES
•These organisms have more than one flagellum.
These flagella enable them to move.
•Flagellates inhabit reproductive tract, alimentary
canal, tissue sites, blood stream, lymph vessels
and cerebrospinal canal
•Imp spp Giardia lamblia
Distribution: Worldwide, more common in hot
climates than temporal regions
Habitat: Upper portions of small intestine. The
disease is called Giardiasis (malabsorbtion
syndrome)
Morphology
• G. lamblia has two morphological
stages: the trophozoite and the
cyst.
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Trophozoite:
pear shaped, with a broad
anterior
10-12µm long and 5-7µm wide
It is also relatively flattened,
with a large sucking disk on
the anterior ventral side, which
serves as the parasite’s
method of attachment to the
mucosa of the host.
The trophozoite also has two
median bodies and four pairs
of flagella (anterior, caudal,
posterior and ventral)
Cyst:
• egg-shaped, and measures 814µm by 7-10µm
• After encystation, each
organelle duplicates, so each
cyst contains four nuclei, four
median bodies, eight pairs of
flagella--although these
organelles are not arraigned in
any clear pattern. Upon
excystation, each cyst
produces two trophozoites.
• The flagella and adhesive disk
are lost as the cyst matures but
median bodies and axoneme
persist.
Giardia Life Cycle
Pathogenesis
• The clinical features associated with Giardia
infection range from total latency (ie,
asymptomatic), to acute self-resolving diarrhea,
to chronic syndromes associated with nutritional
disorders, weight loss and failure to thrive.
• The specific mechanisms of Giardia
pathogenesis leading to diarrhea and intestinal
malabsorption are not completely understood
and no specific virulence factors have been
identified.
• Attachment of trophozoites to the brush border
could produce a mechanical irritation or mucosal
injury.
• In addition, normal villus structure is
affected in some patients. For example,
villus atrophy and crypt cell hypertrophy
and an increase in crypt depth have been
observed to varying degrees..
• Giardia infection can also lead to lactase
deficiency as well as other enzyme
deficiencies in the microvilli.
• This reduced digestion and absorption of
solutes may lead to an osmotic diarrhea.
Clinical signs
The clinical features associated with Giardiasis
range from total latency (ie, asymptomatic), to acute
self-resolving diarrhea, to chronic syndromes
associated with nutritional disorders, weight loss
and failure to thrive.
Children exhibit clinical symptoms more frequently
that adults and subsequent infections tend to be
less severe than initial infections. The incubation
period is generally 1-2 weeks, but ranges of 1-75
days have been reported.
• Anorexia, nausea, and epigastric
uneasiness are additional frequent
complaints during chronic infections. In the
majority of chronic cases the parasites and
symptoms spontaneously disappear.
Diagnosis
Stool Examination:
Stool examination is the preferred method for
Giardia diagnosis. Diagnosis is confirmed by
finding cysts or trophozoites in feces.
Serology /ELISA to detect IgM in serum provides
evidences of current infection