amoebidae

1. ORDER AMOEBIDA
(FAMILY ACANTHAMOEBIDAE)

2. 2
CONTENTS SLIDE
NO.
Introduction 3
Epidemiology 4
Classification 5
Structure & Life Cycle 6
Clinical Manifestation and Pathogenesis 9
Acanthamoeba Keratitis 10
Pathogenesis of Amoebic Keratitis 11
Treatment 12
Prevention & Control 13
Microbiology, Clinical Characteristics, Diagnosis and
Treatment of Free-living Amoebae known to cause
Human Disease
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3. INTRODUCTION
 Small, free living, widely distributed in soil and water.
 Cause diseases in humans and other animals.
 Normally, they live as:
• Phagotrophs- in aquatic habitats where they feed on bacteria.
• Opportunists- in humans, they may produce serious
infection of the central nervous system (CNS) and the eye.
o ‘Amphizoic’ have ability to live in two Worlds, as free-
living organisms and as endoparasites.
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4. EPIDEMIOLOGY
 Aerobic, eukaryotic protists that comprise several genera.
 Worldwide Geographic distribution.
 Found in freshwater, mud and moist soil and normally feeding
on bacteria.
 Hundreds of patients with Central Nervous System (CNS)
invasion by Acanthamoeba spp. and thousands of
Acanthamoeba keratitis have been reported Worldwide.
 Through the late-1990s, 103 cases of meningoencephalitis
due to Acanthamoeba species were reported although that
number is now estimated to be closer to 200 worldwide.
 Acanthamoeba keratitis is much more common, with more
than 3000 cases distributed globally. 4

5. CLASSIFICATION
Kingdom Protista
Sub-Kingdom Protozoa
Phylum Sarcomastigophora
Sub-Phylum Sarcodina
Class Lobosea
Order Amoebida
Family Acanthamoebidae
Genus Acanthamoeba
Species A. astronyxis, A. castellanii,
A. culbertsoni and A.
polyphaga.
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6. STRUCTURE AND LIFE CYCLE
 The nuclei are characterized by a large central nucleolus
or karyosome and a nuclear membrane without
chromatin granules.
 Acanthamoeba has two stages:
1) Trophozoite- an amoeboid form with spine or thorn like
pseudopodia (acanthopodia). 15-25 µm in size. Nucleus is
single with central karyosome and no peripheral chromatin.
2) Cysts- Double walled (outer wrinkled ectocyst and inner
endocyst) with large central, dense nucleolus surrounded by
halo.
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7. Figure No. 1: Acanthamoeba species 7

8. Figure No. 2: Life Cycle of Acanthamoeba spp. showing
stages and proposed portals of entry
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9. CLINICAL MANIFESTATIONS AND
PATHOGENESIS
Two distinct clinical syndromes that infect humans:
1) Granulomatous amoebic encephalitis (GAE)
2) Amoebic keratitis (AK)
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10. ACANTHAMOEBA KERATITIS
Mode of Infection
o Through corneal trauma.
o Exposure to contaminated
water.
o Wearing contaminated
contact lenses.
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11. PATHOGENESIS OF AMOEBIC
KERATITIS
 Mechanism of adhesion-
Mannose binding protein
on Acanthamoeba adheres
to glycoprotein receptors
on corneal epithelium.
 Characterised by- corneal
infiltration and ulcerations,
iritis, scleritis, hypopyon,
severe pain and loss of
vision.
 A. polyphaga and A.
castellanii frequently
identified species in the
corneal scrapping.
Figure No. 3: Acanthamoeba
keratitis with the characteristic
infiltrate
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12. TREATMENT
 Acanthamoeba keratitis may be treated with
antimicrobial agents.
 Treatment is difficult, but some cases have been treated
successfully with ketoconazole, miconazole, and
propamidine isethionate.
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13. PREVENTION & CONTROL
o The Amoebic keratitis, caused by contact lens is
preventable by means of:
• Proper cleaning of contact lenses by using commercial rather
than home made saline solutions.
• Disinfecting contact lenses preferably with a thermal system.
• Not wearing lenses during sleep and while swimming.
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14. MICROBIOLOGY, CLINICAL
CHARACTERISTICS, DIAGNOSIS AND
TREATMENT OF FREE-LIVING AMOEBAE KNOWN
TO CAUSE HUMAN DISEASE
Acanthamoeba spp.
Disease Amoebic keratitis
Epidemiology Corneal trauma; poor contact lens
hygiene.
At risk Contact lens wearers (>80% of
cases)
Signs & Symptoms Intense pain, photophobia, tearing;
dendriform epitheliopathy (early);
stromal ring.
Clinical Course Prodrome of days; subacute to
chronic keratitis. 14

15. CONTINUED…
Laboratory Diagnosis Corneal scraping or biopsy to find
tropozoites or cysts confocal
microscopy.
Distinct Morphologic Features Vesicular nucleus; finger-like
pseudopodia projecting from surface;
Cyst wall with 2 layers and with
pores.
Culture Non-nutrient agar with gram-negative
bacteria; Tissue culture cells (Monkey
kidney cell line, Human Epithelial
type 2 cells-HEp2, Vero and diploid
macrophage cell line); Optimal
growth at 37ºC (CNS isolates) or at
30ºC (corneal isolates).
CT/MRI of head Not applicable.
Antimicrobial therapy Polyhexamethylene biguanide
(PHMB), chlorhexidine, propamidine,
hexamidine, tropical and oral
voriconzole.
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