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Acanthamoeba
Epidemiology:
1) inhabitant of soil & water
2) normally feed on bacteria & water
3) opportunistic infection of human CNS
4) cysts become airborne & may be recovered from the throat & nasal passages
Pathology:
1) granulomatous amoebic meningoecephalitis caused by several species of Acanthamoeba, including:
a) A. castellani
b) A. culbertsoni
c) A. polyphaga
d) A. astronyxis
2) generally subacute or chronic opportunistic infection of chronically ill, debilitated or immunosuppressed patients
3) death generally results in weeks to months after onset of symptoms
4) infection spreads hematogenously from primary foci in skin, pharynx or respiratory
5) reaction to infection is granulomatous
6) trophozoites predominate in viable tissue
7) cysts predominate in areas of necrosis
8) diagnosis generally established at autopsy
Clinical manifestations:
1) initial presentation may be ulcerative skin lesions, subcutaneous abscesses or erythematous nodules
2) granulomatous amoebic meningoencephalitis
3) keratitis
a) daily wear or extended wear of contact lenses in patients with trauma to cornea
b) inadequate hygiene is risk factor
c) paracentral ring infiltration of corneal stroma
d) progression to ulceration & possibly perforation
Laboratory:
1) Acanthamoeba in eye by wet mount
- diagnosis (keratitis) is made by demonstration of trophozoites or cysts in corneal scrapings or biopsy
2) stains
a) Giemsa, PAS or trichrome
b) calcofluor white is helpful for identification of cysts
4) trophozoites
a) measure 15-45 um
b) needle-lie filamentous projections from cell (acanthopodina)
5) cysts
a) measure 10-25 um
b) double-walled with wrinkled outer wall
c) polygonal, setallte or round inner wall
6) Acanthamoeba serology
a) Acanthamoeba antibody in CSF
b) Acanthamoeba antibody in cornea
c) Acanthamoeba antibody in serum
7) Acanthamoeba identified by culture
- culture on agar media
8) Acanthamoeba DNA
9) see ARUP consult [3]
Management:
1) keratoplasty for keratitis
2) amoebic meningoencephalitis
- trimethoprim-sulfamethoxazole in combination with rifampin & ketoconazole
- combination therapy with fluconazole plus sulfadiazine & pyrimethamine
- miltefosine is used as part of combination therapy
- surgical resection of lesions, when possible [4]
- almost uniformly fatal
3) some studies in animals suggest rifampin may be useful
Related
trophozoite
Specific
Acanthamoeba astronyxis
Acanthamoeba castellani
Acanthamoeba culbertsoni
Acanthamoeba polyphaga
General
amoeba
Properties
KINGDOM: animal
PHYLUM: protozoa
References
- Clinical Diagnosis & Management by Laboratory Methods,
19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia,
PA. 1996, pg 1269-70
- Harrison's Principles of Internal Medicine, 14th ed.
Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 1179
- ARUP Consult: Acanthamoeba and Naegleria
The Physician's Guide to Laboratory Test Selection & Interpretation
https://www.arupconsult.com/content/acanthamoeba-and-naegleria
- Samuels MA, Gonzalez RG, Makadzange AT, Hedley-Whyte ET
Case 3-2017 - A 62-Year-Old Man with Cardiac Sarcoidosis
and New Diplopia and Weakness.
N Engl J Med 2017; 376:368-379. January 26, 2017
PMID: 28121502
http://www.nejm.org/doi/full/10.1056/NEJMcpc1610713