free-living amoebae causing human
infections
_ are normal inhabitants of soil and water where they feed on bacteria.
_ A few members have the ability to become facultative parasites when an
opportunity to enter a vertebrate exists.
_There are able to infect humans
Naegleria fowleri
Acanthamoeba spp.
Naegleria fowleri
When a victim swims or
sinks into freshwater.
- all victims have had a
history of swimming in
freshwater lakes or ponds or
swimming pools a few days
before the onset of symptoms
Naegleria fowleri
_ Naegleria fowleri is a free living brain-eating amoeba.
_ Typically found in warm fresh water (thermo tolerant
amoeba).
_ worldwide distribution.
_ It exists in trophozoite and cyst forms and in a transient
flagellate stage.
_ Naegleria fowleri is the causative agent of primary amebic
meningoencephalitis (PAM).
_ The period incubation is short, the symptoms are acute, and
death is almost certain and rapid.
_Naegleria fowleri invades the C.N.S. via penetration of the
olfactory mucosa and nasal tissues (nose).
_ Since Naegleria fowleri trophozoites and cysts are
susceptible to chlorine, swimming pools should be
adequately chlorinated.
Naegleria fowleri
Naegleria fowleri
• Structures of the amoeba form are : Trophozoit and flagellate .
• The infective stage is trophozoit stage
• Method of transmission is by penetrate the mucosal layer of olfactory tissue
and nasal cavity
• Leads to Primary amebic meningoencephalitis
• Most symptoms involving fever , headache, stiff neck and confusion.
• Diagnosis with X-ray , IHAT in CSF.
•Occasionally, a C.T scan may be ordered to rule out cerebral hematoma.
culture media of CSF and PCR .
Acanthamoeba culbertsoni
Free-living trophozoites and cysts occur in both the soil and
freshwater.
Trophozoites occur only as amoeboid forms
Acanthamoeba culbertsoni
• Free-living amoeba
• Lives in water have been found in soil; sea
water; sewage; swimming pools; contact lens
equipment; medicinal pools; dental treatment
units and air conditioning systems
• Contact lens wearers can get keratitis (infection
of the cornea) by using tap water for lens
disinfection or by swimming when wearing
lenses
Acanthamoe
ba
Acanthamoeba
_ Acanthamoeba are ubiquitous organisms in nature.
_ Most species are free-living.
_ Cysts are common and are very resistant to chlorine.
_ Some are opportunists that can cause infections in human.
_ Infections with these amoebae are more common in
immunocompromised patients.
_ Amoebae can be introduced through environmental
exposures, including swimming while wearing contact lenses
or using contaminated contact lens solutions.
_ Acanthamoeba genus causes 3 clinical syndromes:
1 - granulomatous amebic encephalitis (GAE).
2 - Disseminated granulomatous amebic disease (eg, skin,
sinus, and pulmonary infections).
3 - Amebic keratitis: a sight-threatening disease. Most cases
occur in people who wear contact lenses.
Acanthamoeba results in lesions of the skin, eye, brain, etc.
The symptoms of GAE including :
Alter mental status, headache ,fever, neck stiffness,
seizures, focal neurological signs and coma leading
to death
keratitis : corneal inflammation and corneal perforation often followed by blindness.
Laboratory Diagnosis of infections with
free-living amoebae:
• Keratitis:
• Acanthamoeba trophozoites or cysts
can be demonstrated with corneal
scrapings or a biopsy sample via wet
mount, stains, histopathologic
examination.
• Granulomatous amebic encephalitis: _
This condition is diagnosed via brain
biopsy. (cyst and trophozoit)
Flagellate protozoa.
• 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.
Flagellate
Protozoa
Intestinal & urogenital
Blood Flagellate
flagellates
Trichomonas.
Giardia
Chilomastix
Giardia lamblia
Malabsorption
syndrome
(Giardiasis)
Most common intestinal flagellate of humans
 Most common water-borne and food-borne
disease.
 Children
worldwide
Giardia lamblia
• Also known as G. intestinalis or G. duodenalis.
• Diseases: Giardiasis, lambliasis, flagellate diarrhea,
(malabsorbtion syndrome)
• Geographic distribution: world wide, more prevalence in warm
climates.
• Habitat: Upper portions of small intestine.
• Infective state: Cyst
Reservoirs: Men, dogs, cats, wild animals
Mechanisms of Transmission: fecal contamination
Contamination routes: Oral
•
•
•
•
Incubation period bout 2-3 weeks
Resistant to chlorine.
Filtration is necessary to eliminate contamination
Consist of 2 stages: 1)trophozoite 2)cyst
Morphology
• G. lamblia has two morphological
stages: the trophozoite and the
cyst.
•
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.
•
asymptomatic group :

•
Well-nourished children with adequate immune
response and adults who harborfew parasites and / or less
virulent .
symptomatic group :

Generally children under six months, with some degree of
malnutrition or poorimmune response. Characterized by the
large number of parasites present.
Clinical signs
The clinical features associated with Giardiasis
watery foul-smelling diarrhea, abdominal cramps,
flatulence, anorexia, and nausea. are additional
frequent complaints during chronic infections. In the
majority of chronic cases the parasites and
symptoms spontaneously disappear.
Also have fat-soluble deficiencies, folic acid
deficiencies, and structural changes in intestinal
villi.
Children exhibit clinical symptoms more frequently
that adults
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
Examination of duodenal fluid or duodenal
biopsy:To identify Giardia lamblia and other enteric
pathogens.
To visualize changes in histologic features.
Factors that promote infection
•
Poor quality of the means of disposal of garbage and excreta.
Swarm of flies.
•
Fecal contamination of drinking water and irrigation.
•
Poor health education of the population.
•
Artificial feeding of infants (carelessness in the preparation of
bottles).
•
(homosexual).
•
The cyst is viable for two months in cold water and is resistant
to water.
•
Sometimes this infection is a family, and
parents with symptomatic children infected but asymptomatic .
Chilomastix mesnili
– Non-pathogenic; endocommensal.
– Trophs and cysts in the life cycle.
– The cyst stage is resistant to environmental
pressures and is responsible for transmission of
Chilomastix
– Cysts and trophozoites can be found in the feces
(diagnostic stages).
– Worldwide.
– Habitat : the cecum.
– Water borne parasite  infected by contaminated
water.
C. mesnili
• Even though they are not pathogenic
and endocommensal, their presence
indicates poor hygiene practices and
sanitation.
• Because of this need to be able to
distinguish these from pathogenic
organisms.
Chilomastix mesnili
• TROPHOZOITE - 6-24 µm
long by 3-20 µm wide.
• 4 flagella arise from
kinetosomes at
anterior end; 3 flagella
extend anteriorly, 1 extends
into the cytostome (flagella
are difficult to see in stained
trophozoites).
Chilomastix mesnili
• CYST is lemon-shaped;
6 to 10 µm in diameter.
• Contains single
nucleus, cytosome, and
retracted flagella.
Non-Pathogenic
Intestinal Flagellates
Chilomastix mesnili
Life cycle of Chilomastix mesnili
Infection occurs by the
ingestion of cysts in
contaminated water,
food, . In the large (and
possibly small)
intestine, excystation
releases trophozoites.
Chilomastix resides in
the cecum and/or colon;
considered a
commensal organism
Laboratory diagnosis
Pathogenicity: none (if present with large numbers, may
be result in some disturbance).
Microscopic examination:
Stool examination for trophozoites or cysts