Update on Acanthamoeba Keratitis: Diagnosis, Treatment, and Outcomes.

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A literature review to describe the current diagnosis and management of Acanthamoeba keratitis.

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An update on Acanthamoeba keratitis: diagnosis, pathogenesis and treatment

Jacob Lorenzo-Morales, Naveed Khan, Julia Walochnik (2015)

Free-living amoebae of the genus Acanthamoeba are causal agents of a severe sight-threatening infection of the cornea known as Acanthamoeba keratitis. Moreover, the number of reported cases worldwide is increasing year after year, mostly in contact lens wearers, although cases have also been reported in non-contact lens wearers. Interestingly, Acanthamoeba keratitis has remained significant, despite our advances in antimicrobial chemotherapy and supportive care. In part, this is due to an incomplete understanding of the pathogenesis and pathophysiology of the disease, diagnostic delays and problems associated with chemotherapeutic interventions. In view of the devastating nature of this disease, here we present our current understanding of Acanthamoeba keratitis and molecular mechanisms associated with the disease, as well as virulence traits of Acanthamoeba that may be potential targets for improved diagnosis, therapeutic interventions and/or for the development of preventative measures. Novel molecular approaches such as proteomics, RNAi and a consensus in the diagnostic approaches for a suspected case of Acanthamoeba keratitis are proposed and reviewed based on data which have been compiled after years of working on this amoebic organism using many different techniques and listening to many experts in this field at conferences, workshops and international meetings. Altogether, this review may serve as the milestone for developing an effective solution for the prevention, control and treatment of Acanthamoeba infections.

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Use of subgenic 18S ribosomal DNA PCR and sequencing for genus and genotype identification of acanthamoebae from humans with keratitis and from sewage sludge.

Michael J. M. Hay, Susan J. Schroeder, I Niszl … (2001)

This study identified subgenic PCR amplimers from 18S rDNA that were (i) highly specific for the genus Acanthamoeba, (ii) obtainable from all known genotypes, and (iii) useful for identification of individual genotypes. A 423- to 551-bp Acanthamoeba-specific amplimer ASA.S1 obtained with primers JDP1 and JDP2 was the most reliable for purposes i and ii. A variable region within this amplimer also identified genotype clusters, but purpose iii was best achieved with sequencing of the genotype-specific amplimer GTSA.B1. Because this amplimer could be obtained from any eukaryote, axenic Acanthamoeba cultures were required for its study. GTSA.B1, produced with primers CRN5 and 1137, extended between reference bp 1 and 1475. Genotypic identification relied on three segments: bp 178 to 355, 705 to 926, and 1175 to 1379. ASA.S1 was obtained from single amoeba, from cultures of all known 18S rDNA genotypes, and from corneal scrapings of Scottish patients with suspected Acanthamoeba keratitis (AK). The AK PCR findings were consistent with culture results for 11 of 15 culture-positive specimens and detected Acanthamoeba in one of nine culture-negative specimens. ASA.S1 sequences were examined for 6 of the 11 culture-positive isolates and were most closely associated with genotypic cluster T3-T4-T11. A similar distance analysis using GTSA.B1 sequences identified nine South African AK-associated isolates as genotype T4 and three isolates from sewage sludge as genotype T5. Our results demonstrate the usefulness of 18S ribosomal DNA PCR amplimers ASA.S1 and GTSA.B1 for Acanthamoeba-specific detection and reliable genotyping, respectively, and provide further evidence that T4 is the predominant genotype in AK.

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Risk factors for microbial keratitis with contemporary contact lenses: a case-control study.

D Minassian, Shefali Verma, John K G Dart … (2008)

To assess the relative risks (RR) of microbial keratitis (MK) for contemporary contact lens (CL) types and wearing schedules. A 2-year prospective case-control study begun in December 2003. Cases were 367 CL wearers attending Moorfields Eye Hospital with proven or presumed MK. Controls were 1069 hospital controls, who were CL wearers with a disorder unrelated to CL wear, and 639 population-based controls who were CL wearers randomly selected from the Moorfields catchment area. Hospital patients completed a self-administered questionnaire; population-based controls were interviewed by telephone. Multivariate analysis was done both for all cases of MK, and for the moderate and severe MK subgroups alone. The RR for developing MK, and vision loss, for all lens types compared with planned replacement soft lenses (the referent). Compared with planned replacement soft lenses (the referent), the RR of MK was significantly increased with daily disposable (DD) CLs (RR, 1.56x [95% confidence interval (CI), 1.1-2.1]; P = 0.009) and differed between different brands of DD lens, was reduced for rigid lenses (RR, 0.16x [95% CI, 0.06-0.4]; P or=20/40. The RR for overnight wear, for any lens type, was 5.4 times higher (95% CI, 3.3-10.9; P<0.001). Comparison of the DD soft CL types with planned replacement soft lenses (the referent), showed significant differences between brands for the risk of MK. The risk of MK has not been reduced in users of DD and silicone hydrogel CLs. However, vision loss is less likely to occur in DD than in reusable soft CL users. Different brands of CL may be associated with significantly different risks of keratitis; understanding these differences should lead to the development of safer soft lenses. These findings suggest that lens/ocular surface interactions may be more important in the development of corneal infection than oxygen levels and CL case contamination.

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Journal

Journal ID (iso-abbrev): Cornea

Title: Cornea

Publisher: Ovid Technologies (Wolters Kluwer Health)

ISSN (Electronic): 1536-4798

ISSN (Print): 0277-3740

Publication date (Electronic): May 2016

Volume: 35

Issue: 5

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[1 ] Eye Department, Queen Alexandra Hospital, Portsmouth, Hants, United Kingdom.

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DOI: 10.1097/ICO.0000000000000804

PubMed ID: 26989955

SO-VID: 4ed94cf0-92fb-45f3-99f8-0e415b26702d

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Update on Acanthamoeba Keratitis: Diagnosis, Treatment, and Outcomes.

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Most cited references 74

An update on Acanthamoeba keratitis: diagnosis, pathogenesis and treatment

Use of subgenic 18S ribosomal DNA PCR and sequencing for genus and genotype identification of acanthamoebae from humans with keratitis and from sewage sludge.

Risk factors for microbial keratitis with contemporary contact lenses: a case-control study.

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