Acanthamoeba keratitis. A masquerade of presentation in six cases

Use of Amniotic Membrane Transplant and Deep Anterior Keratoplasty in a Patient with Bilateral Acanthamoeba Infectious Keratitis: A Case Report

The aim of this study was to report a case with the use of amniotic membrane transplant and deep anterior keratoplasty in a patient with bilateral Acanthamoeba infectious keratitis as a treatment. A 20-year-old male presented with bilateral Acanthamoeba keratitis (AK) who was initially diagnosed with herpetic keratitis receiving full antiviral and corticosteroid topical treatment without any improvement. Corneal biopsy was performed to confirm the suspected diagnosis, and Acanthamoeba stromal cysts were identified in the sample. Treatment was initiated with 0.02% chlorhexidine, 0.1% propamidine isethionate, neomycin, and tropicamide/phenylephrine. Symptoms and clinical improvement were achieved between the 8th and 10th weeks, so corticosteroids were initiated. Treatment was continued until we observed a poor response in the left eye; therefore, an epithelial scraping and amniotic membrane placement were performed. Lately, the right eye underwent a deep anterior lamellar keratoplasty. A challenging case of bilateral AK managed with topical medications, amniotic membrane, and corneal keratoplasty. The earlier the disease is diagnosed, the better the outcome. If the diagnosis is delayed, the amoebas have penetrated deep into the corneal stroma, and successful therapy becomes difficult. A surgical option can be an early solution with a good prognosis for these cases.

Acanthamoeba keratitis and contact lens wear

Acanthamoeba keratitis is a rare but serious complication of contact lens wear that may cause severe visual loss. The clinical picture is usually characterised by severe pain, sometimes disproportionate to the signs, with an early superficial keratitis that is often misdiagnosed as herpes simplex virus (HSV) keratitis. Advanced stages of the infection are usually characterised by central corneal epithelial loss and marked stromal opacification with subsequent loss of vision. In this paper, six cases of contact lens-related Acanthamoeba keratitis that occurred in Australia and New Zealand over a three-year period are described. Three of the patients were disposable soft lens wearers, two were hybrid lens wearers and one was a rigid gas permeable lens wearer. For all six cases, the risk factors for Acanthamoeba keratitis were contact lens wear with inappropriate or ineffective lens maintenance and exposure of the contact lenses to tap or other sources of water. All six patients responded well to medical therapy that involved topical use of appropriate therapeutic agents, most commonly polyhexamethylene biguanide and propamidine isethionate, although two of the patients also subsequently underwent deep lamellar keratoplasty due to residual corneal surface irregularity and stromal scarring. Despite the significant advances that have been made in the medical therapy of Acanthamoeba keratitis over the past 10 years, prevention remains the best treatment and patients who wear contact lenses must be thoroughly educated about the proper use and care of the lenses. In particular, exposure of the contact lenses to tap water or other sources of water should be avoided.

Diagnosis of Acanthamoeba keratitis in Mashhad, Northeastern Iran: A Gene-Based PCR Assay

Background:

The genus Acanthamoeba is a free-living opportunistic protozoan parasite, which widely distributed in soil and fresh water. Acanthamoeba keratitis, which causes a sight-threating infection of the cornea, is going to rise in Iran and worldwide. The aim of this study was to compare direct microscopy, culture and PCR for detection of Acanthamoeba spp. in clinical samples and to determine the genotypes of Acanthamoeba spp. by sequencing 18SrRNA gene.

Methods:

Among patients clinically suspected to AK referred to a tertiary ophthalmology center at Mashhad, northeastern Iran. During 2017-18, twenty corneal scrapes specimens obtained. The samples were divided into three parts, subjected to direct microscopic examination, culture onto non-nutrient agar and PCR technique. Sensitivity, specificity, accuracy and likelihood ratio were evaluated.

Results:

Among 20 persons clinically suspected to amoebic keratitis, 13(69.2%) patients definitely diagnosed as Acanthamoeba keratitis. Wearing contact lens, eye trauma due to foreign particle and swimming in fresh water were the main predisposing factors. Most of patients suffered from pain and photophobia. Corneal ring infiltration and epithelial defect were common clinical sings. Direct examination had the lowest sensitivity and sensitivity of both Nelson-PCR and JDP-PCR methods were equal and highest. In addition, the results of sequencing identified that all strains belonged to T4 genotype.

Conclusion:

Amoebic keratitis is a sporadic parasitic keratitis, which is mainly seen in contact lens user in Mashhad. PCR based on 18S ribosomal DNA with JDP primers is a reliable and highly sensitive method for diagnosis of Acanthamoeba keratitis in clinically suspected cases.

Effects of Shape and Size of Cobalt Phosphate Nanoparticles against Acanthamoeba castellanii

T4 genotype Acanthamoeba are opportunistic pathogens that cause two types of infections, including vision-threatening Acanthamoeba keratitis (AK) and a fatal brain infection known as granulomatous amoebic encephalitis (GAE). Due to the existence of ineffective treatments against Acanthamoeba, it has become a potential threat to all contact lens users and immunocompromised patients. Metal nanoparticles have been proven to have various antimicrobial properties against bacteria, fungi, and parasites. Previously, different types of cobalt nanoparticles showed some promise as anti-acanthamoebic agents. In this study, the objectives were to synthesize and characterize the size, morphology, and crystalline structure of cobalt phosphate nanoparticles, as well as to determine the effects of different sizes of cobalt metal-based nanoparticles against A. castellanii. Cobalt phosphate octahydrate (CHP), Co₃(PO₄)₂•8H₂O, was synthesized by ultrasonication using a horn sonicator, then three different sizes of cobalt phosphates Co₃(PO₄)₂ were produced through calcination of Co₃(PO₄)₂•8H₂O at 200 °C, 400 °C and 600 °C (CP2, CP4, CP6). These three types of cobalt phosphate nanoparticles were characterized using a field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analysis. Next, the synthesized nanoparticles were subjected to biological assays to investigate their amoebicidal, amoebistatic, anti-encystation, and anti-excystation effects against A. castellanii, as well as cell cytotoxicity. The overall results showed that 1.30 ± 0.70 µm of CHP microflakes demonstrated the best anti-acanthemoebic effects at 100 µg/mL, followed by 612.50 ± 165.94 nm large CP6 nanograins. However, amongst the three tested cobalt phosphates, Co₃(PO₄)₂, the smaller nanoparticles had stronger antiamoebic effects against A. castellanii. During cell cytotoxicity analysis, CHP exhibited only 15% cytotoxicity against HeLa cells, whereas CP6 caused 46% (the highest) cell cytotoxicity at the highest concentration, respectively. Moreover, the composition and morphology of nanoparticles is suggested to be important in determining their anti-acathamoebic effects. However, the molecular mechanisms of cobalt phosphate nanoparticles are still unidentified. Nevertheless, the results suggested that cobalt phosphate nanoparticles hold potential for development of nanodrugs against Acanthamoeba.

Risk Factors for Acanthamoeba Keratitis-A Multistate Case-Control Study, 2008-2011

OBJECTIVE

To identify modifiable risk factors contributing to Acanthamoeba keratitis (AK) infection.

METHODS

A case-control investigation was conducted. Case patients were soft contact lens wearers with laboratory-confirmed AK. Control were soft contact lens wearers ≥12 years of age, with no history of AK. Case patients were recruited from 14 ophthalmology referral centers and a clinical laboratory. Control were matched on state of residence and type of primary eye care provider (ophthalmologist or optometrist). Participants were interviewed using a standardized questionnaire. Univariable and multivariable conditional logistic regression analyses were conducted. Matched odds ratios (mORs) were calculated.

RESULTS

Participants included 88 case patients and 151 matched control. Case patients were more likely to be aged <25 years (unadjusted mOR 2.7, 95% confidence interval 1.3-5.5) or aged >53 years (mOR 2.5, 1.1-5.7), and more likely to be men (mOR 2.6, 1.4-4.8). Unadjusted analyses identified multiple risk factors: rinsing (mOR 6.3, 1.3-29.9) and storing lenses in tap water (mOR 3.9, 1.2-12.3), topping off solution in the lens case (mOR 4.0, 2.0-8.0), having worn lenses ≤5 years (mOR 2.4, 1.3-4.4), rinsing the case with tap water before storing lenses (mOR 2.1, 1.1-4.1), and using hydrogen peroxide (mOR 3.6, 1.1-11.7) versus multipurpose solution. Significant risk factors in multivariable modeling included age >53 years, male sex, topping off, and using saline solution.

CONCLUSIONS

Numerous modifiable risk factors for AK were identified, mostly involving hygiene practices. To reduce the risk of AK, lens wearers should observe recommended lens care practices.

Evaluation of loop-mediated isothermal amplification assay for rapid diagnosis of Acanthamoeba keratitis

BACKGROUND

The clinical features of Acanthamoeba keratitis (AK) are non-specific and closely resemble bacterial, viral and fungal keratitis.

MATERIALS AND METHODS

We compared loop-mediated isothermal amplification (LAMP) with microscopy, non-nutrient agar (NNA) culture and polymerase chain reaction (PCR) in clinical suspects of AK.

RESULTS

Of 52 clinical samples (42 AK suspects and 10 proven bacterial, viral or fungal keratitis), 3 were positive by direct microscopy (sensitivity 60%, confidence interval [CI]: 17%-92.7%), and 5 by NNA culture, 18S rDNA PCR and LAMP (sensitivity 100%, CI: 46.3%-100%). The limit of detection of Acanthamoeba DNA was 1 pg/μl by both LAMP and PCR.

CONCLUSION

PCR and LAMP assays targeting 18S rDNA gene were found particularly suitable for a rapid and accurate diagnosis of AK. LAMP assay takes 2-3 h lesser than PCR, and thus offers a rapid, highly sensitive and specific, simple and affordable diagnostic modality for patients suspected of AK, especially in resource limited settings.

Parasites

Parasites are an important cause of human disease worldwide. The clinical severity and outcome of parasitic disease is often dependent on the immune status of the host. Specific parasitic diseases discussed in this chapter are amebiasis, giardiasis, cryptosporidiosis, cyclosporiasis, cystoisosporiasis, microsporidosis, granulomatous amebic encephalitis, toxoplasmosis, leishmaniasis, Chagas disease, malaria, babesiosis, strongyloidiasis, and scabies.

Development of an immunochromatographic assay kit using fluorescent silica nanoparticles for rapid diagnosis of Acanthamoeba keratitis

We developed an immunochromatographic assay kit that uses fluorescent silica nanoparticles bound to anti-Acanthamoeba antibodies (fluorescent immunochromatographic assay [FICGA]) and evaluated its efficacy for the detection of Acanthamoeba and diagnosis of Acanthamoeba keratitis (AK). The sensitivity of the FICGA kit was evaluated using samples of Acanthamoeba trophozoites and cysts diluted to various concentrations. A conventional immunochromatographic assay kit with latex labels (LICGA) was also evaluated to determine its sensitivity in detecting Acanthamoeba trophozoites. To check for cross-reactivity, the FICGA was performed by using samples of other common causative pathogens of infectious keratitis, such as Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, and Candida albicans. Corneal scrapings from patients with suspected AK were tested with the FICGA kit to detect the presence of Acanthamoeba, and the results were compared with those of real-time PCR. The FICGA kit detected organisms at concentrations as low as 5 trophozoites or 40 cysts per sample. There were no cross-reactivities with other pathogens. The FICGA was approximately 20 times more sensitive than the LICGA for the detection of Acanthamoeba trophozoites. The FICGA kit yielded positive results for all 10 patients, which corresponded well with the real-time PCR results. The FICGA kit demonstrated high sensitivity for the detection of Acanthamoeba and may be useful for the diagnosis of AK.

Do swimming goggles limit microbial contamination of contact lenses?

PURPOSE

Wearing goggles over contact lenses while swimming is often recommended by eye care professionals. Limited data are available to assess this recommendation. The purpose of this study was to examine whether wearing goggles while swimming limits bacterial colonization on contact lenses and whether the type of lens worn affects contamination rates.

METHODS

Twenty-three subjects underwent two swimming sessions at an ocean (salt water) pool (Maroubra beach Rock Pool, Sydney, Australia). Silicone hydrogel (Ciba Focus Night and Day) or hydrogel lenses (Ciba Focus Daily) were inserted into subjects' eyes before 30 min of swimming sessions, and subjects used modified goggles to mimic goggled and non-goggled conditions. At the end of each session, lenses were collected for microbial investigation. Viable bacterial colonies were classified as gram positive and gram negative and enumerated. The level of bacterial colonization on contact lenses between goggled and non-goggled conditions and between the two lens materials were compared.

RESULTS

The range of colony forming units recovered from goggled lenses were 0 to 930 compared with 0 to 1210 on non-goggled lenses. The majority of subjects (16/23) had more microorganisms in the non-goggled condition than when wearing goggles (p = 0.03). Gram negative organisms were found in three non-goggled lenses. No significant difference was shown in the number of bacteria isolated from silicone hydrogel and hydrogel lenses (p > 0.6) irrespective of wearing goggles. Water samples had consistently higher numbers of bacterial counts than those adhered to the lenses; however, no association was found between the number of bacteria in the water sample and those found on the contact lenses.

CONCLUSIONS

Consistently, fewer bacterial colonies were found on the goggled contact lens, thus suggesting goggles offer some protection against bacterial colonization of contact lenses while swimming. These data would support the recommendation encouraging lens wearers to use goggles while swimming.

Resurgence of Acanthamoeba keratitis in Auckland, New Zealand: a 7-year review of presentation and outcomes

PURPOSE

To investigate the presentation, clinical characteristics and outcomes of Acanthamoeba keratitis (AK) in Auckland, New Zealand over a 7-year period.

METHODS

Retrospective analysis of all cases of AK treated by the tertiary corneal service at Auckland City Hospital/ University of Auckland Department of Ophthalmology (August 2001 to May 2008). Data were collected regarding age, gender, contact lens history, presenting signs and symptoms, diagnosis at first presentation, time to final diagnosis, identifiable risk factors, presenting and final visual acuity, results of microbiological testing, medical treatment, surgical interventions, recurrence of disease and length of follow up. All photographs and in vivo confocal microscopy images were reviewed.

RESULTS

Twenty-five eyes of 25 patients were identified with a diagnosis of AK (mean age 40 +/- 13 years). Ninety-six per cent were contact lens wearers. Mean time to diagnosis was 41 +/- 49 days (range 0-181 days, median 21 days). Fourteen patients (56%) had been treated with topical corticosteroids prior to the diagnosis. Early diagnosis of AK (<21 days) was associated with significantly better final visual acuity and did not require any surgical intervention compared with those diagnosed at a later stage. Six patients, all in the late diagnosis group, required surgical intervention.

CONCLUSIONS

AK has become significantly more common in New Zealand in the current decade. This study highlights the fundamental importance of early diagnosis and appropriate management in ensuring favourable outcomes. Practitioners should maintain a clinical suspicion of AK, especially as 96% of the subjects in this study were contact lens wearers.

Updates in Acanthamoeba Keratitis

PURPOSE

Acanthamoeba keratitis is a potentially blinding microbial disease that has been increasing in incidence during the past two decades. Prognosis of this serious disease had been dismal, but improvement in diagnosis, a better understanding of the natural course of the disease, and recent introduction of multiple and effective therapeutic agents have resulted in improvement of visual outcomes.

METHODS

A review of literature pertaining to Acanthamoeba keratitis.

RESULTS

Contact lens wear and exposure to contaminated water sources remain the most important risk factors; however, in vivo confocal microscopy and improved biomicroscopic screening have proven instrumental in accurate early diagnosis. Complications of Acanthamoeba keratitis include dacryoadenitis, corneal melting and scarring, severe secondary glaucoma, cataract, and chronic anterior segment inflammation that can rarely lead to reactive blinding retinal ischemia. Combination chemotherapeutic agents have been shown to be more effective than monotherapy, whereas rehabilitative surgery such as penetrating keratoplasty is best performed on a quiet eye free of ocular inflammation and with no residual amoebae.

CONCLUSIONS

Increased suspicion by clinicians for Acanthamoeba and confocal microscopy have allowed more rapid and accurate diagnosis; treatment with multiple antiamoeba drugs is essential to disease resolution. Provided there are no residual amoebae after treatment, penetrating keratoplasty has been successful in visual rehabilitation. Secondary glaucoma occurs frequently and may require drainage procedures for control of intraocular pressure. Posterior complications are rare but may lead to ischemic retinitis.

[Keratitis due to Acanthamoeba]

Free-living amebae appertaining to the genus Acanthamoeba, Naegleria and Balamuthia are the most prevalent protozoa found in the environment. These amebae have a cosmopolitan distribution in soil, air and water, providing multiple opportunities for contacts with humans and animals, although they only occasionally cause disease. Acanthamoeba spp. are the causative agent of granulomatous amebic encephalitis, a rare and often fatal disease of the central nervous system, and amebic keratitis, a painful disease of the eyes. Keratitis usually follows a chronic course due to the delay in diagnosis and subsequent treatment. The clear increase in Acanthamoeba keratitis in the last 20 years is related to the use and deficient maintenance of contact lenses, and to swimming while wearing them. The expected incidence is one case per 30,000 contact lens wearers per year, with 88% of cases occurring in persons wearing hydrogel lenses. This review presents information on the morphology, life-cycle and epidemiology of Acanthamoeba, as well as on diagnostic procedures (culture), appropriate antimicrobial therapy, and prevention measures.

Prescribing trends in infectious keratitis: a survey of New Zealand ophthalmologists

PURPOSE

To obtain an overview of the treatment of infectious diseases of the cornea by New Zealand ophthalmologists and to analyse the data in the context of evidence-based treatment recommendations.

METHODS

A questionnaire was sent to all New Zealand ophthalmologists. It comprised 23 multiple-choice questions pertaining to the characteristics of the respondents, the nature of their practice and their prescribing preferences in infectious conjunctivitis and keratitis.

RESULTS

Of the 93 ophthalmologists surveyed, 80.6% returned the questionnaire. Of those in clinical practice, 91.4% regularly treated patients with corneal disease. A subspecialty interest in cornea was stated by 12.5% of these. This paper reports observations for adenoviral conjunctivitis and adenoviral, Herpes simplex, varicella zoster, bacterial, acanthamoebal and fungal keratitis. In some conditions prescribing practice varied dramatically, such as in adenoviral conjunctivitis where 50% of respondents prescribed a corticosteroid and 51.6% an antibiotic, whereas 37.5% prescribed only lubrication or no topical treatment. In other conditions there was a high degree of agreement between ophthalmologists; indeed, all ophthalmologists treated Herpes simplex dendritic keratitis with topical acyclovir. No statistically significant differences in prescribing habits were identified between subspecialist and non-subspecialist groups, although some important clinical differences emerged. There were occasional marked differences in response when the age group of respondents was considered, particularly in relation to the management of adenoviral infections and bacterial keratitis.

CONCLUSIONS

The findings of this survey suggest that the majority of New Zealand ophthalmologists generally follow international guidelines for the management of infectious keratitis. The identified variations in management provide a foundation for informed clinical debate and the development of treatment guidelines, in line with evidence-based recommendations.

Severe infective keratitis leading to hospital admission in New Zealand

AIM

To identify key risk factors and the management and outcome of severe infective keratitis leading to public hospital admission in New Zealand.

METHODS

Over a 2 year period, all admissions of presumed infective keratitis to Auckland Hospital were identified. The clinical records of all 103 cases were retrospectively reviewed with respect to clinical features, risk factors, management, and outcomes.

RESULTS

The mean time from first symptoms or signs and presentation to hospital was 8.9 (SD 15.5) days. The majority of subjects, 88%, had at least one of the risk factors commonly associated with infective keratitis including previous ocular surgery (30%), contact lens wear (26%), topical corticosteroid use (25%), and ocular trauma (24%). Corneal scraping was performed in 92% and of a total of 105 scrapes, 71% were positive. Bacteria were isolated in all these cases, the majority being Gram positive organisms (72%). The most common isolates identified were coagulase negative Staphylococcus (16%), Propionibacterium acnes (14%), Staphylococcus epidermidis (11%), and Streptococcus pneumoniae (9%). In addition, yeasts were isolated in 5%, fungi in 4%, virus in 2%, and chlamydia in 1%. Importantly, polymicrobial infection accounted for 33% of culture positive cases. Antimicrobial treatment was changed on the basis of culture results in 17 cases (16.5%). Median initial visual and final best corrected visual acuity was 6/36-6/48 (logMAR 0.86) (IQR 0.39-2.00) and 6/12-6/15 (logMAR 0.360) (IQR 0.15-1.70), respectively. Previous ocular surgery and topical corticosteroid use were significantly associated with poorer visual acuity. The mean hospital stay was 5.8 days and the median 4.0 (IQR 2.0-8.0) days. Longer duration of stay was associated with the presence of hypopyon, larger ulcers, previous ocular surgery, and poor visual acuity.

CONCLUSIONS

Infectious keratitis is an important cause of ocular morbidity. A significant proportion of cases have potentially modifiable risk factors. Previous ocular surgery and topical corticosteroid use, in particular, were associated with poorer visual outcomes. Many cases of severe keratitis might be avoided, or their severity reduced, by appropriate education of patients and ophthalmologists.

Acanthamoeba spp. as agents of disease in humans

Acanthamoeba spp. are free-living amebae that inhabit a variety of air, soil, and water environments. However, these amebae can also act as opportunistic as well as nonopportunistic pathogens. They are the causative agents of granulomatous amebic encephalitis and amebic keratitis and have been associated with cutaneous lesions and sinusitis. Immuno compromised individuals, including AIDS patients, are particularly susceptible to infections with Acanthamoeba. The immune defense mechanisms that operate against Acanthamoeba have not been well characterized, but it has been proposed that both innate and acquired immunity play a role. The ameba's life cycle includes an active feeding trophozoite stage and a dormant cyst stage. Trophozoites feed on bacteria, yeast, and algae. However, both trophozoites and cysts can retain viable bacteria and may serve as reservoirs for bacteria with human pathogenic potential. Diagnosis of infection includes direct microscopy of wet mounts of cerebrospinal fluid or stained smears of cerebrospinal fluid sediment, light or electron microscopy of tissues, in vitro cultivation of Acanthamoeba, and histological assessment of frozen or paraffin-embedded sections of brain or cutaneous lesion biopsy material. Immunocytochemistry, chemifluorescent dye staining, PCR, and analysis of DNA sequence variation also have been employed for laboratory diagnosis. Treatment of Acanthamoeba infections has met with mixed results. However, chlorhexidine gluconate, alone or in combination with propamidene isethionate, is effective in some patients. Furthermore, effective treatment is complicated since patients may present with underlying disease and Acanthamoeba infection may not be recognized. Since an increase in the number of cases of Acanthamoeba infections has occurred worldwide, these protozoa have become increasingly important as agents of human disease.

Locally administered ocular corticosteroids: benefits and risks

Corticosteroids, used prudently, are one of the most potent and effective modalities available in the treatment of ocular inflammation. However, they can produce a plethora of adverse ocular and systemic events. In order to optimise and target drug delivery, whilst minimising systemic adverse effects, a diverse range of local ophthalmic preparations and delivery techniques have been developed. Topical drops and ointments remain the primary methods for administration of ocular corticosteroids. However, ocular penetration of topical corticosteroid drops depends upon drug concentration, chemical formulation of corticosteroid, and composition of the vehicle, therefore, apparently small modifications in preparations can produce a more than 20-fold difference in intraocular drug concentration. Periocular injections of corticosteroids continue to have a useful, but limited, therapeutic role and longer acting, intraocular delayed-release devices are in early clinical studies. Although newer corticosteroids with lesser pressure elevating characteristics have been developed, corticosteroid-induced ocular hypertension and glaucoma continue to be significant risks of local and systemic administration. Posterior subcapsular cataract, observed following as little as 4 months topical corticosteroids use, is thought to be due to covalent binding of corticosteroid to lens protein with subsequent oxidation. Inappropriate use of topical corticosteroid in the presence of corneal infections also continues to be a cause of ocular morbidity. Other risks of locally administered ophthalmic corticosteroids include: tear-film instability, epithelial toxicity, crystalline keratopathy, decreased wound strength, orbital fat atrophy, ptosis, limitation of ocular movement, inadvertent intraocular injection, and reduction in endogenous cortisol. This extensive review assesses the therapeutic benefits of locally administered ocular corticosteroids in the context of the risks of adverse effects.

Patient characteristics, diagnosis, and treatment of non-contact lens related Acanthamoeba keratitis

AIM

To review the clinical characteristics, diagnosis, and visual outcome in patients with non-contact lens related Acanthamoeba keratitis and compare the findings with reported series of contact lens associated Acanthamoeba keratitis.

METHODS

Medical and microbiology records of 39 consecutive patients with a diagnosis of Acanthamoeba keratitis, at a tertiary eyecare centre in India between January 1996 and June 1998, were analysed retrospectively.

RESULTS

A majority of the patients presented with poor visual acuity and large corneal stromal infiltrates (mean size 38.20 (SD 26. 18) mm). A predisposing factor was elicited in 19/39 (48.7%) patients (trauma 15, dirty water splash three, leaf juice one). None of the patients had worn contact lenses. Most patients (26/39 (66. 6%)) came from a low socioeconomic background. Complaint of severe pain was not a significant feature and radial keratoneuritis was seen in 1/39 (2.5%) patients. A ring infiltrate was present in 41.1% of cases. A clinical diagnosis of fungal keratitis was made in 45% of the patients before they were seen by us. However, all patients were diagnosed microbiologically at our institute based on demonstration of Acanthamoeba cysts in corneal scrapings (34/39) and/or culture of Acanthamoeba (34/39). Treatment with biguanides (PHMB, 15/38 (39.4%), PHMB with CHx, 23/38 (60.5%), one patient did not return for treatment) resulted in healing with scar formation in 27 out of 31(87.0%) followed up patients (mean time to healing 106.9 days). Overall visual outcome was poor with no statistical difference between cases diagnosed within 30 days (early) or 30 days after (late) start of symptoms. The visual outcome in cases requiring tissue adhesive (five) and keratoplasty (three) was also poor.

CONCLUSIONS

This is thought to be the largest series of cases of Acanthamoeba keratitis in non-contact lens wearers. In such cases, the disease is advanced at presentation in most patients, pathognomonic clinical features are often not seen, disease progression is rapid, and visual outcome is usually poor. Possible existence of Acanthamoeba pathotypes specifically associated with non-contact lens keratitis and unique to certain geographical areas is suggested.

Antimicrobial susceptibility of 19 Australian corneal isolates of Acanthamoeba

PURPOSE

To determine the in vitro drug susceptibility of Australian corneal isolates of Acanthamoeba and to correlate the results with patient treatment and visual outcome.

METHODS

Acanthomoeba isolates were obtained from a reference laboratory Cyst suspensions were prepared from 19 strains and exposed to 10 antimicrobial agents for 7 days. The minimum drug concentrations required to inhibit excystation were determined. Inhibited cells were then plated out to determine minimum cysticidal concentrations.

RESULTS

Overall, propamidine proved to be the most active anti-Acanthamoeba agent tested. The disinfectant polyhexamethylene biguanide, either pure or in Baquacil, was also effective. Pentamidine, hexamidine, chlorhexidine and chloroxylenol had intermediate activity, while neomycin, amphotericin B and povidone-iodine had poor activity. There was no clear relationship between in vitro susceptibility and visual outcome.

CONCLUSIONS

Propamidine and polyhexamethylene biguanide drops are recommended as initial choices for the treatment of Acanthamoeba keratitis. The variability in the susceptibility to any one agent suggests that individual testing of isolates is necessary to identify the most appropriate treatment. A number of factors influence visual outcome in these cases; further studies are required to resolve the importance or otherwise of in vitro susceptibility.

Fluorescent oligonucleotide probes for clinical and environmental detection of Acanthamoeba and the T4 18S rRNA gene sequence type

The first genus- and subgenus-specific fluorescent oligonucleotide probes for in situ staining of Acanthamoeba are described. Sequences of these phylogeny-based probes complement the 18S rRNA and the gene encoding it (18S rDNA). The genus-specific probe (GSP) is a fluorescein-labeled 22-mer specific for Acanthamoeba as shown here by its hybridization to growing trophozoites of all 12 known Acanthamoeba 18S rDNA sequence types and by its failure to hybridize with amoebae of two other genera (Hartmannella vermiformis and Balamuthia mandrillaris), two human cell lines, and two bacteria (Pseudomonas aeruginosa and Escherichia coli). The sequence type T4-specific probe (ST4P) is a rhodamine-labeled 30-mer specific for Acanthamoeba 18S rDNA sequence type T4, as shown here in hybridization tests with trophozoites of all 12 sequence types. T4 is the subgenus group associated most closely with Acanthamoeba keratitis (AK). GSP also was tested with corneal scrapings from 17 patients with a high index of clinical suspicion of AK plus 5 patient controls. GSP stained both trophozoites and cysts, although nonspecific cyst wall autofluorescence also was observed. Results could be obtained with GSP in 1 to 2 days, and based on results from cell culture tests, the probe correctly detected the presence or absence of Acanthamoeba in 21 of 24 specimens from the 22 patients. The use of GSP with cultured trophozoites and cysts from corneal scrapings has illustrated the suitability of using fluorescent oligonucleotide probes for identification of the genus Acanthamoeba in both environmental and clinical samples. In addition, the use of ST4P with cultured amoebae has indicated the potential of oligonucleotide probes for use in subgenus classification.

Correlation between surface water contamination with amoeba and the onset of symptoms and diagnosis of amoeba-like keratitis

AIM

A seasonal variation was noted in the incidence of amoeba-like keratitis in Iowa. The level of contamination of amoeba in surface water has been found previously to vary on a monthly basis for Tulsa, Oklahoma, a region with a similar climate. It was hypothesised that this seasonal variation in amoeba-like keratitis correlated with the concentration of amoeba in surface water.

METHODS

The monthly variation in the onset of symptoms was determined and date of diagnosis in 137 cases of amoeba-like keratitis, in Iowa, from January 1993 to the end of December 1996.

RESULTS

Over a 4 year period a significant variation was found, on a monthly basis, in the onset of symptoms as reported by the patient. There were two peak periods per year when the onset of symptoms was most frequent: June and November. This corresponded closely with the concentration of amoeba in the ground water reported for a similar region in the mid-west (Tulsa, Oklahoma). A yearly increase was found in the number of cases diagnosed from January 1993 to the end of December 1996.

CONCLUSIONS

This study supports the hypothesis that the concentration of amoeba in surface water may influence the rate of an amoeba-like keratitis infection.

Acanthamoeba keratitis in New Zealand, including two cases with in vivo resistance to polyhexamethylene biguanide

BACKGROUND

Acanthamoeba keratitis is an uncommon corneal infection that can run a protracted course with, at times, serious visual results. Eighty-five per cent of cases occur in soft contact lens wearers. The first New Zealand case occurred in 1990 and only seven cases have been identified in New Zealand to the end of 1996.

METHODS

We surveyed the ophthalmologists looking after these seven cases of acanthamoeba keratitis as to time to diagnosis, treatment and outcome.

RESULTS

New Zealand has a low incidence of this disease. All cases were soft contact lens wearers with defective care in every instance. After an initial two late-diagnosed cases, the time to diagnosis for four of the five other cases has been within 2 weeks. Medical treatment has varied over this series, but since the introduction of the cationic antiseptics polyhexamethylene biguanide (PHMB) and chlorhexidine in 1992, the last five cases were all treated with PHMB. One case diagnosed within 2 weeks ran a devastating course, despite intensive PHMB, and a second case remained culture positive after 1 year of PHMB and the late addition of chlorhexidine. Debridement, 0.1% PHMB and hexamidine eventually settled this eye.

CONCLUSIONS

For treatment PHMB, hexamidine rather than propamidine and surgical debridement are favoured. While all Acanthamoeba isolates show good in vitro sensitivity to PHMB, the in vivo response is not always proportionate. A bacterial endosymbiont may have been a factor in the favourable outcome of one protracted case.

Acanthamoeba keratitis

Acanthamoeba species are an important cause of microbial keratitis that may cause severe ocular inflammation and visual loss. The first cases were recognized in 1973, but the disease remained very rare until the 1980s, when an increase in incidence mainly associated with contact lens wear was reported. There is an increased risk when contact lens rinsing and soaking solutions are prepared with nonsterile water and salt tablets. The clinical picture is often characterized by severe pain with an early superficial keratitis that is often treated as herpes simplex infection. Subsequently a characteristic radial perineural infiltration may be seen, and ring infiltration is common. Limbitis and scleritis are frequent. Laboratory diagnosis is primarily by culture of epithelial samples inoculated onto agar plates spread with bacteria. Direct microscopy of samples using stains for the cyst wall or immunostaining may also be employed. A variety of topically applied therapeutic agents are thought to be effective, including propamidine isethionate, clotrimazole, polyhexamethylene biguanide, and chlorhexidine. Various combinations of these and other agents have been employed, often resulting in medical cure, especially if treatment is commenced early in the course of the disease. Penetrating keratoplasty is preferably avoided in inflamed eyes, but may be necessary in severe cases to preserve the globe or, when the infection has resolved, to restore corneal clarity for optical reasons.

Severe microbial keratitis in temperate and tropical Western Australia

To determine the patterns of severe microbial keratitis in Western Australia, all acute admissions over a 2 year period to the Department of Ophthalmology, Royal Perth Hospital were assessed. Fifty-three cases (n = 53) of severe, presumed microbial keratitis were identified. Seventy per cent of these eyes had a visual acuity of 6/60 or less on admission and only 38.8% had 6/12 or better corrected acuity following resolution of the keratitis. The most commonly identified predisposing factors were: prior ocular surgery with or without exposed monofilament sutures (43.4%); contact lens wear (22.6%); lid malposition (17.0%); history of ocular trauma (15.1%); and history of previous herpes simplex keratitis (13.2%). It is notable that 26.4% of the subjects had been applying topical ophthalmic corticosteroids prior to admission. Following corneal scrape or biopsy a positive microbial diagnosis was made in 71% of samples, with Gram-negative and Gram-positive bacterial isolates being equally frequent. Five cases of Acanthamoeba keratitis were identified following corneal biopsy. Where antibiotic sensitivities were available, it was noted that 61.5% of Gram-positive and 46.1% of Gram-negative bacteria were susceptible to chloramphenicol, with 84.6% of Gram-negative bacteria being sensitive to gentamicin. Many of these severe cases of microbial keratitis might have been avoided, or their severity lessened, by earlier identification of predisposing risk factors, more intensive and appropriate antibiotic administration, and improved patient education following ocular surgery.

Outbreak of keratitis presumed to be caused by Acanthamoeba

PURPOSE

A sharp increase of Acanthamoeba keratitis from two cases per year to 30 cases per year at our institution prompted this study to determine whether there was a change in the clinical characteristics, basic epidemiology, and outcome of this disease.

METHODS

We reviewed all cases of Acanthamoeba keratitis diagnosed at the University of Iowa Hospitals and Clinics from mid-1993 through 1994.

RESULTS

We screened 217 patients with keratitis by tandem scanning confocal microscopy and suspected Acanthamoeba in 51 patients. Diagnosis was confirmed by cytology in 43 patients (48 eyes). There were no positive cultures. Patients examined within four weeks of onset of symptoms were younger (mean age, 32.6 +/- 15.4 years) and wore contact lenses (11 of 18 patients), and infrequently herpes simplex keratitis (four of 18 patients) was diagnosed. Patients examined after four weeks were older (mean age, 54.0 +/- 19.5 years), infrequently wore contact lenses (six of 25 patients), and often had herpes simplex keratitis (12 of 25 patients).

CONCLUSIONS

Corneal examination with tandem scanning confocal microscopy was associated with a marked increase in the detection of Acanthamoeba, strongly suggesting that the disease is more prevalent than suspected. Acanthamoeba may account for many cases of clinically presumed herpes simplex keratitis, the leading cause of corneal blindness in the United States. Acanthamoeba should be considered in the differential diagnosis of any unexplained keratitis, even those of short duration.

Decreased corneal sensation as an initial feature of Acanthamoeba keratitis

BACKGROUND

Herpes simplex keratitis is the most common misdiagnosis in patients with Acanthamoeba keratitis, which is increasing in frequency and is associated with daily wear soft contact lenses. Both entities usually present as unilateral keratitis. The manifestations of superficial Acanthamoeba keratitis (i.e., unilaterality, dendriform appearance, positive response to antivirals, and decreased corneal sensation) increase the opportunity for misdiagnosis as herpes simplex keratitis. The authors have encountered six patients with Acanthamoeba keratitis in whom the correct diagnosis was delayed from 2 weeks to 3 months.

METHODS

All six patients underwent testing with the Cochet-Bonnet esthesiometer and extensive pharmacologic treatment for herpes simplex keratitis. Corneal scrapings were taken between 2 and 6 weeks after the initial examination.

RESULTS

In all six patients, corneal sensation was decreased significantly. Drug therapy was ineffective. Cultures were positive for Acanthamoeba. Five of six patients underwent penetrating keratoplasty.

CONCLUSIONS

Decreased corneal sensation has contributed to the misdiagnosis of Acanthamoeba as herpes simplex keratitis. Misdiagnosis results in delayed treatment and worse outcome. The authors found that significantly decreased corneal sensation is a frequent finding in early Acanthamoeba keratitis. Therefore, physicians should consider Acanthamoeba keratitis as an alternative diagnosis in patients with presumed herpes simplex keratitis with decreased corneal sensation.