Dr.%20Amira%20Taman

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Free-Living Amoebae

• Dr. Amira Taman

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General characters(free-living)

• Free-living
• Opportunistic pathogens in human (under unknown
  conditions).
• Widely distributed in soil and water.
• Naegleria fowleri and Acanthamoeba castellani

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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
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Naegleria fowleri

• Free-living in fresh or brackish water (lake,
  river and ponds) and soil.
• Morphology
• Amoebo-flagellate
• Three forms
• Amoeboid
• Flagellate
• Cyst

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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

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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

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Cyst form

• Rounded with single nucleus
• 7-15u
• Thick double cyst wall
• Found in soil
• Never in tissue

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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

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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

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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

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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.

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Prevention

• Public education
• Chlorination of swimming pools and public water
  public supplies

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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.

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• Trophozoite
• Variable in shape 10-40 u in diameter
• slender spine-like projections of plasma
  membrane (acantopodia).
• Contractile vacuole
• Nucleus with large central karyosome

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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)

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• 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.

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• 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.

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• 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

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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.

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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

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Characters Naegleria Acanthamoeba
Forms Trophozoite Cyst 3 stages Trophozoite, flagellate and cyst Actively motile Round Two only Trophozoite and cyst Sluggishly motile polyhedral
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• 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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