dr. amira taman free-living amoebae. amoebae parasitic pathogenic entamoeba histolytica commensal...
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Dr. Amira Taman
Free-Living Amoebae
General charactersGeneral characters(free-living)(free-living)
Free-living
Opportunistic pathogens in human (under unknown conditions).
Widely distributed in soil and water.
Naegleria fowleri and Acanthamoeba castellani
Features Intestinal amoebae
Free-living amoebae
Habitat
Pathogenicity
Flagellated forms
Intestine
Pathogenic (diseases in colon, liver and other extra-intestinal sites)
Absent
Soil and water
Opportunistic (affect CNS, cornea and skin)
May be present
Naegleria fowleriNaegleria fowleriFree-living in fresh or brackish water (lake, river and
ponds) and soil.
MorphologyAmoebo-flagellate
Three forms Three forms AmoeboidFlagellateCyst
Amoeboid (Trophozoite )
Rounded / elongated 15-30u. The infective stage
Single nucleus Feed and divide by binary fission.
Can be transformed into flagellate and cyst formFound in CSF and tissue
Flagellate formFlagellate form
Elongated / pear shaped
Anterior nucleusTwo free flagella
Found in water at 27-37 3C
Non feeding & non dividing
Never present in tissueNever present in tissueCan be transformed to amoeboid form Can be transformed to amoeboid form
Cyst formCyst form
oRounded with single nucleuso7-15u
oThick double cyst wall
oFound in soiloNever 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 adultPreviously 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 38.2-40Stiff neck, mental status changes and seizures
DiagnosisDiagnosisHistory of swimming in pools or natural warm waterClinical picture
CSF fresh film 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. ColiLeucocytosis in peripheral blood (25,000)Serodiagnosis not useful, PCR, CT
Treatment of PAMTreatment of PAM
No satisfactory treatment.HospitalizationPalliative treatment
Amphotericin B “drug of choice”. Act on amoebic plasma membrane .IV or intrathecal
Miconazole, rifampin and sulfisoxazole.
PreventionPrevention
Public educationChlorination of swimming pools and public water public supplies
Acanthamoeba castellani 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 vacuoleNucleus with large central
karyosome
cystcystPolygonal, 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 entrySkin, 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 keratitisSevere unilateral ocular painVision is affected, neutrophils infiltrationsLoss of vision
Trophozoite and cyst are present in corneal tissue
3) chronic granulomatous skin ulcers
Laboratory diagnosis
Brain tissue and CSF Trophozoite and cystCulture 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 availableSulfadiazine, penicillin and chloramophenicol.
In keratitis, drug is effective (ketoconazole) with topical application ( miconazole) followed by keratoplasty.
Prevention Health educationAvoid swimming in stagnant waterUse of proper contact lens fluid
Characters Naegleria Acanthamoeba
Forms
Trophozoite
Cyst
3 stages Trophozoite, flagellate and cyst
Actively motile
Round
Two onlyTrophozoite and cyst
Sluggishly motile
polyhedral
Amoeba affecting brain
1ry amoebic meningoencephalitis (PAM)Granulomatous amoebic encephalitis (GAE)Amoebic brain abscess.
Amoeba affecting skin
- Granulomatous skin ulcer
- Cutaneous amoebiasis
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