Acanthamoeba are free-living amoebae found worldwide in soil and water that can cause disease in humans. They have two life stages - a trophozoite stage and a cyst stage. They are known to cause Acanthamoeba keratitis through corneal trauma or contact lens use, as well as granulomatous amoebic encephalitis. Acanthamoeba keratitis is difficult to treat but can be managed with antimicrobial agents like propamidine isethionate and contact lens use should involve proper cleaning and disinfection to prevent infection.

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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