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