Diagnosis and treatment of Acanthamoeba Keratitis: A scoping review demonstrating unfavorable outcomes

Acanthamoeba Keratitis Management and Prognostic Factors: A Systematic Review

Background/Objectives: The aim of this study was to review the therapeutic and prognostic factors influencing Acanthamoeba Keratitis (AK) management. Methods: A systematic search was performed across MEDLINE® (via PubMed), Web of Science®, and Scopus®, following the PRISMA 2020 guidelines, and registered in PROSPERO (CRD420251010774). Studies reporting AK treatment regiments and prognostic factors were included. After extracting the data from the included articles, the relevant aspects of the treatment and the prognostic factors were compared and summarized. Results: Sixty-one articles were included: nine were prospective, including 3 randomized controlled trials (RCTs), and fifty-two were retrospective. The findings suggest that therapeutic epithelial debridement (TED), followed by an association with biguanides, diamidines, and an antibacterial agent, is a strong initial treatment option. An adjunctive medical treatment with topical voriconazole 1% or oral miltefosine may also be considered. Surgical approaches were also assessed when the pharmaceutical therapy failed, with Deep Anterior Lamellar Keratoplasty (DALK) playing an important role in the cases without a deep stroma involvement. Early Therapeutic Penetrating Keratoplasty (TPK) should be used as a salvage therapy and Optical Penetrating Keratoplasty (OPK) should be used for rehabilitation purposes. Key prognostic factors include older age, delayed diagnosis, corticosteroid use before prompt diagnosis, poor initial best corrected visual acuity (BCVA), and AK stage at presentation. Conclusions: The initial treatment with TED, biguanides, and diamidines remains the foundation of treatment. Surgical options can be considered in advanced cases. An early diagnosis, age, and initial BCVA are prognosis factors that should be considered. Future research may focus on improvement of protocols and searching for novel agents.

Effectiveness of phytoproducts against pathogenic free-living amoebae - A scoping and critical review paving the way toward plant-based pharmaceuticals

Infections caused by free-living amoebae (FLA) have increased worldwide and are expected to worsen. The lack of drugs that are effective (especially against cysts), affordable, and safe to treat these infections exacerbates the concern. Plants present a promising source of bioactive compounds for developing effective drugs; however, the scientific literature on this topic has yet to be adequately synthesized. This work provides a critical scoping review summarizing the amoebicidal performance of plant-derived products and their potential for developing effective drugs to treat FLA infections. Out of 5889 articles retrieved from multiple databases, 119 articles were selected, from which data on 180 plant species belonging to 127 genera and 62 families were extracted. The extracts, essential oils, and compounds from these plants exhibited a diverse range of potency against cysts and trophozoites. Among the compounds studied, periglaucine A, kolavenic acid, and (+)-elatol are promising cysticidal drug candidates due to their high potency, as well as their known low toxicity to non-target cells. Tovophillin A, gartinin, 8-deoxygartinin, garcinone E, 9-hydroxycalabaxanthone, γ-mangostin, and borneol also exhibit high cysticidal potency, but their selectivity profile is unknown. Resveratrol, rosmarinic acid, β-amyrin, and vanillic acid stand out for their high potency against trophozoites and low toxicity to mammalian cells. Another group of compounds with similarly high trophocidal potency includes (-)-epicatechin, (-)-epigallocatechin, apigenin, costunolide, demethoxycurcumin, kaempferol, methyl-β-orcinolcarboxylate, sakuraetin, (+)-elatol, debromolaurinterol, luteolin, (-)-rogiolol, cystomexicone B, epigallocatechin gallate, quercetin, and α-bisabolol. These compounds are priority candidates for further studies on in vivo efficacy, safety, pharmacokinetics, and pharmacodynamics.

Imidazolium salt as potent Amoebicide for rapid inactivation of Acanthamoeba spp. trophozoites and cysts

Acanthamoeba spp. are amphizoic protozoa capable of causing several severe diseases in humans and other animals, including granulomatous amoebic encephalitis and Acanthamoeba keratitis (AK). The high resistance of Acanthamoeba genus, especially in its cystic form, to most conventional disinfectants poses a challenge for its management through aseptic practices based on chemical disinfectants. The imidazolium salt (IS) (C16MImCl) demonstrated significant acanthamoebicidal potency against both trophozoites and cysts. However, its biocidal efficacy over a short exposure time, which will shed light on its potential use as a disinfectant, still needs to be studied. Therefore, the acanthamoebicidal effect of IS against trophozoites and cysts of Acanthamoeba polyphaga and Acanthamoeba spp. exposed for 5 and 20 min to concentrations of 250, 125, 62.5, 31.25, 15.62, and 7.81 μg/mL was evaluated in the present study. Exposure of trophozoites of both strains to IS for 20 min significantly reduced trophozoite viability at concentrations ≥62.5 μg/mL. All trophozoites of both strains were inactived 20 min after cessation of IS exposure at concentrations of ≥125 μg/mL for 5 min or ≥15 μg/mL for 20 min. Cyst viability of all strains was significantly reduced after 20 min of exposure to IS at 62.5 and 125 μg/mL, based on the viability exclusion assay with trypan blue dye. However, all cysts exposed to IS at ≥ 125 μg/mL for 20 or 5 min were unable to excyst when incubated for 10 days on non-nutrient agar with Escherichia coli. The acanthamoebicidal efficacy of IS, upon short exposure to concentrations below the cytotoxic value for human keratinocyte cells (IC50 = 171.50 μg/mL), combined with its previously reported bactericidal and fungicidal effects, suggests that IS has the potential to be used in the formulation of multipurpose disinfectants.

Targets for the diagnosis of Acanthamoeba eye infections include four cyst wall proteins and the mannose-binding domain of the trophozoite mannose-binding protein

Acanthamoebae, which are free-living amoebae, cause corneal inflammation (keratitis) and blindness, if not quickly diagnosed and effectively treated. The walls of Acanthamoeba cysts contain cellulose and have two layers connected by conical ostioles. Cysts are identified by in vivo confocal microscopy of the eye or calcofluor-white- or Giemsa-labeling of corneal scrapings, both of which demand great expertise. Trophozoites, which use a mannose-binding protein to adhere to keratinocytes, are identified in eye cultures that delay diagnosis and treatment. We recently used structural and experimental methods to characterize cellulose-binding domains of Luke and Leo lectins, which are abundant in the inner layer and ostioles. However, no antibodies have been made to these lectins or to a Jonah lectin and a laccase, which are abundant in the outer layer. Here, confocal microscopy of rabbit antibodies (rAbs) to recombinant Luke, Leo, Jonah, and laccase supported localizations of GFP-tagged proteins in walls of transfected Acanthamoebae. rAbs efficiently detected calcofluor white-labeled cysts of 10 of the 11 Acanthamoeba isolates tested, including six T4 genotypes that cause most cases of keratitis. Further, laccase shed into the medium during encystation was detected by an enzyme-linked immunoassay. Structural and experimental methods identified the mannose-binding domain (ManBD) of the Acanthamoeba mannose-binding protein, while rAbs to the ManBD efficiently detected DAPI-labeled trophozoites from all 11 Acanthamoeba isolates tested. We conclude that antibodies to four cyst wall proteins and the ManBD efficiently identify Acanthamoeba cysts and trophozoites, respectively.IMPORTANCEFree-living amoeba in the soil or water cause Acanthamoeba keratitis, which is diagnosed by identification of unlabeled cysts by in vivo confocal microscopy of the eye or calcofluor-white (CFW) labeled cysts by fluorescence microscopy of corneal scrapings. Alternatively, Acanthamoeba infections are diagnosed by the identification of trophozoites in eye cultures. Here, we showed that rabbit antibodies (rAbs) to four abundant cyst wall proteins (Jonah, Luke, Leo, and laccase) each efficiently identify CFW-labeled cysts of 10 of the 11 Acanthamoeba isolates tested. Further, laccase released into the medium by encysting Acanthamoebae was detected by an enzyme-linked immunoassay. We also showed that rAbs to the mannose-binding domain (ManBD) of the Acanthamoeba mannose-binding protein, which mediates adherence of trophozoites to keratinocytes, efficiently identify DAPI-labeled trophozoites of all 11 Acanthamoeba isolates tested. In summary, four wall proteins and the ManBD appear to be excellent targets for the diagnosis of Acanthamoeba cysts and trophozoites, respectively.

A case series of overnight orthokeratology-related Acanthamoeba keratitis in Northwest China: Clinical presentation, management, and outcomes

PURPOSE

To report a series of overnight orthokeratology-related Acanthamoeba keratitis (OK-AK) at a teriary transfer care eye hospital in China from January 1, 2021, to February 29, 2024, and to provide a reference for its treatment.

METHODS

This was a single-center, retrospective case study. Records of patients with a history of OK lens use who were diagnosed with AK were analyzed. Data on clinical presentation, management, and outcomes were analyzed. We also preliminarily investigated behaviors associated with the risk of OK-AK.

RESULTS

A total of 11 patients were included (8 females, 3 males, 14 eyes). The mean age was 14.7 ± 3.6 years (range: 11-22 years). All patients were using OK for an average of 3.5 ± 2.4 years (range: 1-8 years) before the onset of AK. The median time from onset of symptoms to diagnosis was 5 days (range: 2-150 days). The most frequently presented symptoms were blurred vision (n=11, 100%), redness (n=8, 72.7%), and excruciating eye pain (n=8, 72.7%). Topical anti-amoebic agents (a combination of topical polyhexamethylene biguanide [PHMB], metronidazole, and voriconazole) were used in all infected eyes once the AK diagnosis was made. Systemic metronidazole and/or voriconazole were added in stromal keratitis. Eight eyes (57.1%) were cured by medication. The remaining eyes (6/14, 42.9%) underwent therapeutic keratoplasty surgery because of poor response or rapid progression of the disease. The surgeries included two lamellar keratoplasty (ALK), one deep lamellar keratoplasty (DALK), and three therapeutic penetrating keratoplasty (TPK). Recurrence occurred in two cases (2/6, 33.3%), one after 1 year following DALK and the other 3 months after TPK. All patients had improved visual acuity after treatment.

CONCLUSION

This findings indicate that OK-AK is a serious problem in Northwest China. AK should be suspected early in patients with OK lens use who present with clinical symptoms such as eye redness and pain. The medication cure rate in OK-AK was 57.1%. The early keratoplasty surgery rate was 42.9%, and the risk of post-operation recurrence should be a concern. Based on the above findings, clinicians need to establish a standardized follow-up system and carry out multi-dimensional user education.

A Synthetic View on Acanthamoeba Keratitis Host Immune Response: Potential Factors Influencing the Development of Chronic Inflammation

PURPOSE

The purpose of this study was to compile the current knowledge concerning Acanthamoeba keratitis (AK) host immune response to better understand the elements involved in the chronification of inflammation and worse disease outcomes.

METHODS

A scoping review of the literature on AK host immune response was written after a systematic literature search was performed on the PubMed, Latin American Caribbean Health Sciences Literature, Cochrane Library, Embase, Web of Science, and Scientific Electronic Library Online databases. Recovered articles were screened according to inclusion and exclusion criteria, and the selected studies were analyzed to compile the review.

RESULTS

The search strategy yielded a total of 768 articles from all searched databases. After the exclusion of duplicate records, 412 studies were screened according to inclusion and exclusion criteria. Finally, a total of 95 articles were selected to compile this review, of which 15 were included as additional bibliography. As for study type, 45 were experimental, 19 were observational, 23 were case reports, and 8 were reviews.

CONCLUSIONS

From the literature, both innate and adaptive immune systems seem to play an important role in AK control and resolution. On the other hand, there is also abundant evidence pointing out that the development of chronic and extracorneal inflammation is immune mediated and is influenced by several factors such as individual patient genetic variability, inadequate treatment, and Acanthamoeba strain pathogenicity.

A Narrative Review of Acanthamoeba Isolates in Malaysia: Challenges in Infection Management and Natural Therapeutic Advancements

Acanthamoeba, a free-living amoeba (FLA) found in diverse ecosystems, poses significant health risks globally, particularly in Malaysia. It causes severe infectious diseases, e.g., Acanthamoeba keratitis (AK), primarily affecting individuals who wear contact lenses, along with granulomatous amoebic encephalitis (GAE), a rare but often life-threatening condition among immunocompromised individuals. AK has become increasingly prevalent in Malaysia and is linked to widespread environmental contamination and improper contact lens hygiene. Recent studies highlight Acanthamoeba's capacity to serve as a "Trojan horse" for amoeba-resistant bacteria (ARBs), contributing to hospital-associated infections (HAIs). These symbiotic relationships and the resilience of Acanthamoeba cysts make treatment challenging. Current diagnostic methods in Malaysia rely on microscopy and culture, though molecular procedures like polymerase chain reaction (PCR) are employed for more precise detection. Treatment options remain limited due to the amoeba's cyst resistance to conventional therapies. However, recent advancements in natural therapeutics, including using plant extracts such as betulinic acid from Pericampylus glaucus and chlorogenic acid from Lonicera japonica, have shown promising in vitro results. Additionally, nanotechnology applications, mainly using gold and silver nanoparticles to enhance drug efficacy, are emerging as potential solutions. Further, in vivo studies and clinical trials must validate these findings. This review highlights the requirement for continuous research, public health strategies, and interdisciplinary collaboration to address the growing threat of Acanthamoeba infections in Malaysia while exploring the country's rich biodiversity for innovative therapeutic solutions.

Identification of new targets for the diagnosis of cysts (four) and trophozoites (one) of the eye pathogen Acanthamoeba

Acanthamoebae , which are free-living amoebae, cause corneal inflammation (keratitis) and blindness, if not diagnosed and effectively treated. While trophozoites adhere to and damage the cornea, Acanthamoeba cysts, the walls of which contain cellulose and have two layers connected by conical ostioles, are the diagnostic form by microscopy of the eye or of corneal scrapings. We recently used structural and experimental methods to characterize cellulose-binding domains of Luke and Leo lectins, which are abundant in the inner layer and ostioles. However, no antibodies have been made to these lectins or to a Jonah lectin and a laccase, which are abundant in the outer layer. Here we used confocal microscopy to show that rabbit antibodies to recombinant Luke, Leo, Jonah, and laccase generally support localizations of GFP-tagged proteins in walls of transfected Acanthamoebae. Rabbit antibodies to all four wall proteins efficiently detected calcofluor white-labeled cysts of 10 of 11 Acanthamoeba isolates obtained from the ATCC, including five T4 genotypes that cause most cases of keratitis. Laccase shed into the medium during encystation was detected by an enzyme-linked immunoassay. We also used structural and experimental methods to characterize the mannose-binding domain of an Acanthamoeba mannose-binding protein and showed that rabbit antibodies to the mannose-binding domain efficiently detected trophozoites of all 11 Acanthamoeba isolates. We conclude that four wall proteins are all excellent targets for diagnosing Acanthamoeba cysts in the eye or corneal scrapings, while the mannose-binding domain is an excellent target for identifying trophozoites in cultures of corneal scrapings.

Importance

Free-living amoeba in the soil or water cause Acanthamoeba keratitis, which is diagnosed by identification of cysts by microscopy of the eye or of corneal scrapings, using calcofluor-white that unfortunately cross-reacts with fungi and plants. Alternatively, Acanthamoeba infections are diagnosed by identification of trophozoites in cultures of scrapings. Here we showed that rabbit antibodies to four abundant cyst wall proteins (Jonah, Luke, Leo, and laccase) each efficiently detect calcofluor-white-labeled cysts of 10 of 11 Acanthamoeba isolates obtained from the ATCC. Further, laccase released into the medium by encysting Acanthamoebae was detected by an enzyme-linked immunoassay. We also showed that rabbit antibodies to the mannose-binding domain of the Acanthamoeba mannose-binding protein, which mediates adherence of trophozoites to keratinocytes, efficiently identifies trophozoites of all 11 ATCC isolates. In summary, four wall proteins and the ManBD appear to be excellent targets for diagnosis of Acanthamoeba cysts and trophozoites, respectively.

Anti-Acanthamoebic effects of silver-conjugated tetrazole nanoparticle

Tetrazoles are five-membered ring aromatic heterocyclic molecules that consist of one carbon and four nitrogen atoms. Several tetrazole-based drugs have shown promising activities against bacteria, fungi, asthma, cancer, hypertension etc. The overall aim of this study was to determine anti-Acanthamoebic properties of tetrazoles and tetrazole-conjugated silver nanoparticles. Tetrazole-conjugated silver nanoparticles were synthesized and confirmed using ultraviolet-visible spectrometry, Dynamic light scattering, and Fourier-transform infrared spectroscopy. Using amoebicidal, encystment, and excystment assays, the findings revealed that tetrazoles exhibited antiamoebic properties and these effects were enhanced when conjugated with silver nanoparticles. Importantly, conjugation with silver nanoparticles inhibited parasite-mediated human cell death in vitro, as measured by lactate dehydrogenase release, but it reduced toxic effects of drugs alone on human cells. Overall, these results showed clearly that tetrazoles exhibit potent antiamoebic properties which can be enhanced by conjugation with silver nanoparticles and these potential in the rational development of therapeutic interventions against parasitic infections such as keratitis and granulomatous amoebic encephalitis due to pathogenic Acanthamoeba.

Infectious Keratitis in Patients Over 65: A Review on Treatment and Preserving Eyesight

Infectious keratitis (IK) represents a significant global health concern, ranking as the fifth leading cause of blindness worldwide despite being largely preventable and treatable. Elderly populations are particularly susceptible due to age-related changes in immune response and corneal structure. However, research on IK in this demographic remains scarce. Age-related alterations such as increased permeability and reduced endothelial cell density further compound susceptibility to infection and hinder healing mechanisms. Additionally, inflammaging, characterized by chronic inflammation that develops with advanced age, disrupts the ocular immune balance, potentially exacerbating IK and other age-related eye diseases. Understanding these mechanisms is paramount for enhancing IK management, especially in elderly patients. This review comprehensively assesses risk factors, clinical characteristics, and management strategies for bacterial, viral, fungal, and acanthamoeba keratitis in the elderly population, offering crucial insights for effective intervention.

Clinical outcomes and prognostic factors in Acanthamoeba keratitis

PURPOSE

To report clinical findings and prognostic factors for visual and morphological outcomes in patients with Acanthamoeba keratitis (AK).

METHODS

Single-center, retrospective, longitudinal study of 51 cases of AK diagnosed by real-time polymerase chain reaction (RT-PCR) between March 2010 and October 2022. The primary outcome was the final best corrected visual acuity (BCVA). Poor visual outcome was defined as a final BCVA ≥ 1 logMAR unit, while good visual outcome was defined as a final BCVA < 1 logMAR unit. Eyes from these two groups were compared, regarding demographic and initial clinical variables, anti-Acanthamoeba treatment used, and complications of the disease. Early diagnosis was defined as ≤ 14 days from symptom onset to diagnostic confirmation and initiation of Acanthamoeba medical treatment. Multivariable logistic regression was used to determine predictors of poor visual outcome.

RESULTS

A total of 51 eyes from 46 patients diagnosed with AK, all contact lens (CL) wearers, were included in this study. Average follow-up was 39.0 ± 30.2 [total range 14-120] months. Thirty-one eyes (60.8 %) presented good visual outcome, with a lower baseline age (30.5 ± 9.0 vs. 42.3 ± 15.8; p = 0.020), better initial BCVA (0.8 ± 0.7 logMAR units vs. 1.3 ± 0.9 logMAR units; p = 0.047), higher rate of early diagnosis (45.2 % vs. 5.6 %; p = 0.004), and higher rate of therapeutic epithelial debridement (64.5 % vs. 10 %; p < 0.001). 20 eyes (39.2 %) presented poor visual outcome, with 12 eyes undergoing evisceration/enucleation (23.5 %). These 20 eyes presented a higher rate of complications (90 % vs. 61.3 %; p = 0.031). In multivariable analysis, early diagnosis of AK (OR 19.78; 95 % CI 2.07-189.11; p = 0.010) and therapeutic epithelial debridement (OR 19.02; 95 % CI 3.27-110.57; p = 0.001) were associated with a good visual outcome.

CONCLUSIONS

In the present study, poor visual outcome was present in 39 % of affected eyes. Early AK diagnosis (≤14 days from symptom onset) and therapeutic epithelial debridement were associated with good final visual outcome.