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Free-Living Amoebae
Dr. Amira Taman
Amoebae
Parasitic
Pathogenic
Entamoeba histolytica
Free-living
Commensal
Entamoeba coli
-Naegleria fowleri
-Acanthamoeba
castellani
General characters
(free-living)
 Free-living
 Opportunistic pathogens in human (under unknown conditions).
 Widely distributed in soil and water.
 Naegleria fowleri and Acanthamoeba castellani
Features
Habitat
Pathogenicity
Intestinal
amoebae
Intestine
Free-living
amoebae
Soil and water
Pathogenic
Opportunistic
(diseases in colon, (affect CNS,
liver and other
cornea and skin)
extra-intestinal
sites)
Flagellated forms Absent
May be present
Naegleria fowleri
Free-living in fresh or brackish water (lake, river and
ponds) and soil.
Morphology
Amoebo-flagellate
Three forms
Amoeboid
Flagellate
Cyst
Amoeboid (Trophozoite )
Rounded / elongated 15-30u.
The infective stage
Single nucleus
Feed and divide by binary fission.
Can be transformed into flagellate
and cyst form
Found in CSF and tissue
Flagellate form
Elongated / pear shaped
Anterior nucleus
Two free flagella
Found in water at 27-37 ̊C
Non feeding & non dividing
Never present in tissue
Can be transformed to amoeboid form
Cyst form
oRounded with single nucleus
o7-15u
oThick double cyst wall
oFound in soil
oNever in tissue
Infection
 Swimming or diving in warm water(aspiration of water)
contaminated with N. Fowleri (trophzoite) esp. in summer.
 Trophozoit is neurotropic ( nose- olf mucosa-olf pulb-cribriform
plate-subarachinoid space).
 1ry amoebic meningoencephalitis (fatal)
- haemorrhagic inflammation
- necrosis of brain tissue
- Amoeba is the only form detected in brain tissue,
flagellates and cysts never found in tissue or CSF
1ry amoebic meningoencephalitis
 Children and young adult
 Previously healthy
 History of bathing, swimming, diving or playing
in warm stagnant, fresh water
 Few days to 2 weeks prior to onset of symptoms
 Headache, temp 38.2-40
 Stiff neck, mental status changes and seizures
Diagnosis
 History of swimming in pools or natural warm water
 Clinical picture
 CSF fresh film (amoeboid), purulent but no bacteria.
Increase pressure, PMN cells , increase protein, presence
of RBCs
 Stained : giemsa, trichrome and Wright stains
 Culture on non-nutrient agar plate seeded with E. Coli
 Leucocytosis in peripheral blood (25,000)
 Serodiagnosis not useful, PCR, CT
Treatment of PAM
No satisfactory treatment.
 Hospitalization
 Palliative treatment
 Amphotericin B “drug of choice”.
 Act on amoebic plasma membrane .
 IV or intrathecal
 Miconazole, rifampin and sulfisoxazole.
Prevention
Public education
Chlorination of swimming pools and public water
public supplies
Acanthamoeba castellani
 In dust, soil, sand, river ponds and tape water.
 2 forms: Trophozoite and Cyst (infective stages).
 Both stages may exist in the environment and tissues.
 In man : affect CNS, eye, skin and lungs.
 Opportunistic parasite, causes severe disease in
immunocompromised.
Trophozoite
 Variable in shape 10-40 u in
diameter
 slender spine-like projections of
plasma membrane
(acantopodia).
 Contractile vacuole
 Nucleus with large central
karyosome
cyst
 Polygonal, spherical; or star-
shaped.
 15-20u in diameter
 Double wall, outer smooth
irregular ectocyst and inner rough
polyhedral endocyst with many
pores (osteoles)
Portal of entry
Skin, mucosal ulcer, lung inhalation or cornea.
Mode of infection
Inhalation of aerosol or dust containing cyst
or trophozoites.
Invasion through broken skin.
Corneal trauma, prolonged use of contact
lenses.
Diseases
 1) Granulomatous
amoebic encephalitis:
 Affects immunocompromised
Course is sub-acute or chronic (from weeks to years)
 Reaches brain through blood supply from lung or skin
abrasions.
 forms focal granuloma at deeper brain tissues
Headache, seizures, stiff neck, nausea and vomiting
Tissues contain Trophozoite, cysts and multinucleate
giant cells.
 2) Amoebic keratitis:
 Direct contact of cornea with contaminated water or
contact lens
 Chronic progressive, ulcerative keratitis
 Severe unilateral ocular pain
 Vision is affected, neutrophils infiltrations
 Loss of vision
 Trophozoite and cyst are present in corneal tissue
 3) chronic granulomatous skin ulcers
Laboratory diagnosis
 Brain tissue and CSF
Trophozoite and cyst
 Culture on non nutrient agar
 CSF elevated protein, normal or decrease glucose.
 Corneal scraping (direct saline wet mount)
 Culture of contact lens saline or corneal scraping
 CT multiple brain focal lesions.
 IFA of tissue.
Treatment
 No effective therapy is available
 Sulfadiazine, penicillin and chloramophenicol.
 In keratitis, drug is effective (ketoconazole) with topical
application ( miconazole) followed by keratoplasty.
Prevention
 Health education
 Avoid swimming in stagnant water
 Use of proper contact lens fluid
Characters
Naegleria
Acanthamoeba
Forms
3 stages
Trophozoite,
flagellate and cyst
Two only
Trophozoite and
cyst
Trophozoite Actively motile
Sluggishly
motile
Cyst
polyhedral
Round
Amoeba affecting brain
 1ry amoebic meningoencephalitis (PAM)
 Granulomatous amoebic encephalitis (GAE)
 Amoebic brain abscess.
Amoeba affecting skin
- Granulomatous skin ulcer
- Cutaneous amoebiasis