Acanthamoeba
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Epidemiology
- inhabitant of soil & water
- normally feed on bacteria & water
- opportunistic infection of human CNS
- cysts become airborne & may be recovered from the throat & nasal passages
Pathology
- granulomatous amoebic meningoecephalitis caused by several species of Acanthamoeba, including:
- A. castellani
- A. culbertsoni
- A. polyphaga
- A. astronyxis
- generally subacute or chronic opportunistic infection of chronically ill, debilitated or immunosuppressed patients
- death generally results in weeks to months after onset of symptoms
- infection spreads hematogenously from primary foci in skin, pharynx or respiratory
- reaction to infection is granulomatous
- trophozoites predominate in viable tissue
- cysts predominate in areas of necrosis
- diagnosis generally established at autopsy
Clinical manifestations
- initial presentation may be ulcerative skin lesions, subcutaneous abscesses or erythematous nodules
- granulomatous amoebic meningoencephalitis
- keratitis
- daily wear or extended wear of contact lenses in patients with trauma to cornea
- inadequate hygiene is risk factor
- paracentral ring infiltration of corneal stroma
- progression to ulceration & possibly perforation
Laboratory
- Acanthamoeba in eye by wet mount
- diagnosis (keratitis) is made by demonstration of trophozoites or cysts in corneal scrapings or biopsy
- stains
- Giemsa, PAS or trichrome
- calcofluor white is helpful for identification of cysts
- trophozoites
- measure 15-45 um
- needle-lie filamentous projections from cell (acanthopodina)
- cysts
- measure 10-25 um
- double-walled with wrinkled outer wall
- polygonal, setallte or round inner wall
- Acanthamoeba serology
- Acanthamoeba identified by culture
- Acanthamoeba DNA
- see ARUP consult[3]
Management
- keratoplasty for keratitis
- 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
- some studies in animals suggest rifampin may be useful
More general terms
More specific terms
Additional terms
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
- ↑ 3.0 3.1 ARUP Consult: Acanthamoeba and Naegleria The Physician's Guide to Laboratory Test Selection & Interpretation https://www.arupconsult.com/content/acanthamoeba-and-naegleria
- ↑ 4.0 4.1 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 <PubMed> PMID: https://www.ncbi.nlm.nih.gov/pubmed/28121502 <Internet> http://www.nejm.org/doi/full/10.1056/NEJMcpc1610713