Order amoebidae

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 14

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. ‘ Amphizoic ’ have ability to live in two Worlds, as free-living organisms and as endoparasites . 3

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 . 5

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: 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. Cysts- Double walled (outer wrinkled ectocyst and inner endocyst ) with large central, dense nucleolus surrounded by halo. 6

7. Figure No. 1: Acanthamoeba species 7

8. Figure No. 2: Life Cycle of Acanthamoeba spp. s howing stages and proposed portals of entry 8

9. CLINICAL MANIFESTATIONS and PATHOGENESIS Two distinct clinical syndromes that infect humans: Granulomatous amoebic encephalitis (GAE) Amoebic keratitis (AK) 9

10. Acanthamoeba Keratitis Mode of Infection Through corneal trauma. Exposure to contaminated water. Wearing contaminated contact lenses. 10

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 11

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 . 12

13. PREVENTION & CONTROL 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. 13

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 . 15