Successful Strategic Management of Pythium insidiosum Keratitis with Antibiotics

A masked study to differentiate in vivo confocal microscopic features of Pythium insidiosum and fungal filaments

PURPOSE

To describe in vivo confocal microscopic features of Pythium insidiosum in patients with Pythium keratitis and compare with those observed in fungal keratitis.

METHOD

We collected in vivo confocal images of the cornea from patients with microbiologically confirmed Pythium and fungal keratitis, analysing five putative distinguishing features: filament width (broad or thin), granularity within the filament (present or absent), filament continuity or traceability, the presence or absence of loops, and the double track sign. Three masked observers were shown images with concealed identities and tasked with detecting Pythium filaments. After initial assessment and training, their detection rates were calculated and compared before and after training. We did perform imageJ (Open Source software project Fiji) analysis of all the images for objectively assessment.

RESULTS

Sixty confocal images of Pythium (n = 32,15 patients) and fungal (n = 28,12 patients) keratitis were analysed. The continuity of filaments and the presence of loops emerged as strong predictors of Pythium, with adjusted odds ratios (OR) of 18.1 and 19.29, respectively, based on multivariate logistic regression and decision tree splits. Pre-training accuracy was 0.51, 0.52, and 0.56, but post-training (95 % CI) improved to 0.75 (0.62-0.85), 0.80 (0.67-0.89), and 0.86 (0.75-0.94). Correct identification rates for Pythium were 27, 28, and 29 (84-89 %) out of 32, and for fungus were 16, 21, and 24 (57.4-85.7 %) out of 28 images with sensitivity and specificity ranging from 70.7 to 87.5 % and 80-85 % respectively. ImageJ analysis revealed a significant difference between Pythium and fungal filaments in both width (9.30 ± 1.21 μ vs. 6.20 ± 0.88 μ, p < 0.001) and branching angle (83.92 ± 13.57° vs. 55.10 ± 6.03°, p < 0.001).

CONCLUSIONS

Based on our analysis, these features may be indicative of Pythium and could serve as a helpful reference for future prospective studies. However, further large scale studies and validation are needed to strengthen these observations.

Treating Pythiosis with Antibacterial Drugs Targeting Protein Synthesis: An Overview

This review article explores the effectiveness of antibacterial drugs that inhibit protein synthesis in treating pythiosis, a difficult-to-treat infection caused by Pythium insidiosum. The article highlights the susceptibility of P. insidiosum to antibacterial drugs, such as macrolides, oxazolidinones, and tetracyclines. We examine various studies, including in vitro tests, experimental infection models, and clinical case reports. Based on our synthesis of these findings, we highlight the potential of these drugs in managing pythiosis, primarily when combined with surgical interventions. The review emphasizes the need for personalized treatment strategies and further research to establish standardized testing protocols and optimize therapeutic approaches.

Depth, size of infiltrate, and the microbe - The trio that prognosticates the outcome of infective keratitis

PURPOSE

To analyze the influence of infiltrate size, depth, and organism on the outcome of microbial keratitis.

DESIGN

Retrospective comparative study.

METHODS

Medical records of patients with infective keratitis, who reported from January 2015 to December 2019 to a tertiary eye care center, were analyzed. Size and depth of ulcer at presentation were the factors used to group patients, and the influence on the outcome of the organism causing it was analyzed. Grouping was as follows: group A: ulcer size <6 mm/anterior to midstromal infiltrate, group B: ulcer < 6 mm/full-thickness infiltrate, group C: ulcer >6 mm/anterior to midstromal infiltrate, group D: ulcer > 6 mm/full-thickness infiltrate. Patients with viral keratitis or unidentified organism were excluded. Response to treatment and best-corrected visual acuity (BCVA) at the final follow-up were the outcome measures.

RESULTS

In the study, 1117/6276 patients were included, with 60.8% patients in group A. A significant improvement in visual acuity was noted in groups A/B compared to groups C/D. Group A had the best response to medical management, irrespective of the organism. Higher risk for surgery was noted in group C compared to group B, with group A as the reference. Overall resolution with medical treatment was noted in 70% miscellaneous keratitis, 64.8% bacterial keratitis, 64.3% mixed keratitis, 62.5% acanthamoeba keratitis, 52.6% fungal keratitis, and 12.1% Pythium keratitis. Bacteria and acanthamoeba responded better to medical management than fungal keratitis, whereas Pythium had the highest risk for surgery.

CONCLUSION

An interplay between virulence of the organism along with depth and size of the infiltrate determines the outcome of microbial keratitis.

Randomized Double-Masked Placebo-Controlled Trial for the Management of Pythium Keratitis: Combination of Antibiotics Versus Monotherapy

PURPOSE

The aim of this study was to compare the efficacy of monotherapy (topical linezolid 0.2%) versus a combination of antibiotics (topical linezolid 0.2% and topical azithromycin 1%) for the treatment of Pythium insidiosum keratitis.

METHODS

Cases of P. insidiosum keratitis were prospectively randomized into group A on topical 0.2% linezolid along with topical placebo (sodium carboxymethyl cellulose [CMC] 0.5%) and group B on a combination of topical 0.2% linezolid and topical 1% azithromycin. Both groups were compared by proportion of both clinical resolution and worsening of keratitis along with the number of therapeutic penetrating keratoplasty (TPK) performed at 3 months.

RESULTS

We initially planned N = 66 patients but later limited to 20 (N = 10 in each group) patients owing to one interim analysis. The average size of the infiltrate in group A and B was 5.6 ± 1.5 mm and 4.8 ± 2.0 mm, respectively, with a mean Logarithm of the Minimum Angle of Resolution (logMAR) visual acuity of 2.74 ± 0.55 and 1.79 ± 1.19. At 3 months, from group A, 7 (70%) patients needed TPK and 2 patients had signs of resolution, whereas from group B, 6 (60%) patients achieved complete resolution ( P = 0.0003) and 2 were improving while only 1 needed TPK ( P = 0.02). The median duration of treatment in group A and B, with the study drugs, was 31 days (17.8-47.8) and 101.5 days (80-123.3), P value = 0.003, respectively. Final visual acuity at 3 months was 2.50 ± 0.81 and 0.75 ± 0.87, P = 0.02, respectively.

CONCLUSIONS

A combination of topical linezolid and topical azithromycin was found to have superior efficacy than the monotherapy with topical linezolid for the management of Pythium keratitis.

Outcomes of therapeutic penetrating keratoplasty in Pythium insidiosum keratitis managed with a combination of antibiotics

Purpose

To describe the clinical outcomes of therapeutic penetrating keratoplasty (TPK) in patients with Pythium insidiosum keratitis following treatment with anti-pythium therapy (APT) consisting of linezolid and azithromycin.

Methods

A retrospective review of medical records from May 2016 to December 2019 of patients with P. insidiosum keratitis was carried out. Patients who were treated with APT for a minimum of 2 weeks and then subsequently underwent TPK were included in the study. Data on demographic characteristics, clinical features, microbiology characteristics, and intraoperative details, postoperative outcomes were documented.

Results

A total of 238 cases of Pythium keratitis were seen during the study period and 50 cases that satisfied the inclusion criteria were included. The median of the geometric mean of the infiltrate was 5.6 mm (IQR 4.0-7.2 mm). The patients received topical APT for a median of 35 days (IQR 25-56) prior to surgery. The most common indication of TPK was worsening keratitis (41/50, 82%). No recurrence of infection was observed. An anatomically stable globe was noted in 49/50 eyes (98%). The median graft survival rate was 2.4 months. A clear graft was present in 10 eyes (20%) with a final median visual acuity of 20/125 after a median follow-up period of 18.4 months (IQR 11-26 months). Graft size of less than 10 mm [OR: 5.824 (CI:1.292-41.6), P = 0.02] was found to be significantly associated with a clear graft.

Conclusion

Performing TPK following the administration of APT has good anatomical outcomes. A smaller graft of <10 mm was associated with a higher chance of graft survival.

Pythium insidiosum keratitis: Review of literature of 5 years' clinical experience at a tertiary eye care center

BACKGROUND

Pythium insidiosum is an important cause of infectious keratitis from tropical and sub-tropical countries. Due to its closely mimicking clinical and microbiological features with fungus, it remained unidentified and managed as fungal keratitis for a long time. Previously all patients had poor outcomes with antifungal therapy and needed surgical treatment with higher rates of recurrences of infection leading to loss of an eye. Thus, a novel approach was required to treat it and, in this article, we would like to elaborate on the drastic change which these 5 years have brought in the management of this condition.

METHODS

In view of making a consolidated article comprising all the required information and also our clinical experience in the management of Pythium keratitis, we extensively reviewed several articles available on it over PubMed and Google scholars. Relevant literature describing details about Pythium, its clinical correlation, and recent advances from 52 articles including 12 articles from our group were finally included.

RESULTS

Our group identified and highlighted the unique clinical and microbiological features of Pythium insidiosum, performed several in-vitro, in-vivo studies along with clinical trials, and proposed the strategic way of its diagnosis and treatment. The use of antifungals was replaced with antibacterial medications and this resulted in better medical and surgical outcomes.

CONCLUSION

The diagnosis and management of Pythium insidiosum is constantly evolving with several recent works pointing out the possible changes in the practice patterns for the management of this challenging form of keratitis.

Selection of an Appropriate In Vitro Susceptibility Test for Assessing Anti-Pythium insidiosum Activity of Potassium Iodide, Triamcinolone Acetonide, Dimethyl Sulfoxide, and Ethanol

The orphan but highly virulent pathogen Pythium insidiosum causes pythiosis in humans and animals. Surgery is a primary treatment aiming to cure but trading off losing affected organs. Antimicrobial drugs show limited efficacy in treating pythiosis. Alternative drugs effective against the pathogen are needed. In-house drug susceptibility tests (i.e., broth dilution, disc diffusion, and radial growth assays) have been established, some of which adapted the standard protocols (i.e., CLSI M38-A2 and CLSI M51) designed for fungi. Hyphal plug, hyphal suspension, and zoospore are inocula commonly used in the drug susceptibility assessment for P. insidiosum. A side-by-side comparison demonstrated that each method had advantages and limitations. Minimum inhibitory and cidal concentrations of a drug varied depending on the selected method. Material availability, user experience, and organism and drug quantities determined which susceptibility assay should be used. We employed the hyphal plug and a combination of broth dilution and radial growth methods to screen and validate the anti-P. insidiosum activities of several previously reported chemicals, including potassium iodide, triamcinolone acetonide, dimethyl sulfoxide, and ethanol, in which data on their anti-P. insidiosum efficacy are limited. We tested each chemical against 29 genetically diverse isolates of P. insidiosum. These chemicals possessed direct antimicrobial effects on the growth of the pathogen in a dose- and time-dependent manner, suggesting their potential application in pythiosis treatment. Future attempts should focus on standardizing these drug susceptibility methods, such as determining susceptibility/resistant breakpoints, so healthcare workers can confidently interpret a result and select an effective drug against P. insidiosum.

Pythium insidiosum Keratitis: Past, Present, and Future

Pythium insidiosum (PI) is an oomycete, a protist belonging to the clade Stramenopila. PI causes vision-threatening keratitis closely mimicking fungal keratitis (FK), hence it is also labeled as "parafungus". PI keratitis was initially confined to Thailand, USA, China, and Australia, but with growing clinical awareness and improvement in diagnostic modalities, the last decade saw a massive upsurge in numbers with the majority of reports coming from India. In the early 1990s, pythiosis was classified as vascular, cutaneous, gastrointestinal, systemic, and ocular. Clinically, morphologically, and microbiologically, PI keratitis closely resembles severe FK and requires a high index of clinical suspicion for diagnosis. The clinical features such as reticular dot infiltrate, tentacular projections, peripheral thinning with guttering, and rapid limbal spread distinguish it from other microorganisms. Routine smearing with Gram and KOH stain reveals perpendicular septate/aseptate hyphae, which closely mimic fungi and make the diagnosis cumbersome. The definitive diagnosis is the presence of dull grey/brown refractile colonies along with zoospore formation upon culture by leaf induction method. However, culture is time-consuming, and currently polymerase chain reaction (PCR) method is the gold standard. The value of other diagnostic modalities such as confocal microscopy and immunohistopathological assays is limited due to cost, non-availability, and limited diagnostic accuracy. PI keratitis is a relatively rare disease without established treatment protocols. Because of its resemblance to fungus, it was earlier treated with antifungals but with an improved understanding of its cell wall structure and absence of ergosterol, this is no longer recommended. Currently, antibacterials have shown promising results. Therapeutic keratoplasty with good margin (1 mm) is mandated for non-resolving cases and corneal perforation. In this review, we have deliberated on the evolution of PI keratitis, covered all the recently available literature, described our current understanding of the diagnosis and treatment, and the potential future diagnostic and management options for PI keratitis.

Unusual Presentation of Pythium Keratitis as Peripheral Ulcerative Keratitis: Clinical Dilemma

PURPOSE

To describe the clinical picture and outcome of a case of Pythium keratitis, presenting as peripheral ulcerative keratitis (PUK).

CASE SUMMARY

A 54- year- old male presented to the clinic with a PUK in the right eye. Systemic investigations were performed to rule out associated collagen vascular disorders. Microbiological examination of corneal scrapings was performed to rule out secondary infection which revealed gram positive cocci on Gram stain. There was no growth of any organism on culture. Topical vancomycin 5% and ciprofloxacin 0.3% were started initially. On regular follow-up, there was worsening of clinical signs. Topical and oral corticosteroids were further added. Due to progressive worsening of infiltrate size and corneal perforation, therapeutic penetrating keratoplasty was performed. Pythium insidiosum (confirmed by DNA sequencing and zoospore formation) was grown from excised corneal button and the histopathology revealed filaments suggestive of Pythium species.

CONCLUSION

This case describes the uncommon manifestation of Pythium insidiosum keratitis presenting as peripheral ulcerative keratitis.

Pythium insidiosum keratitis - A review

Pythium insidiosum is an oomycete and is also called “parafungus” as it closely mimics fungal keratitis. The last decade saw an unprecedented surge in Pythium keratitis cases, especially from Asia and India, probably due to growing research on the microorganism and improved diagnostic and treatment modalities. The clinical features such as subepithelial infiltrate, cotton wool-like fluffy stromal infiltrate, satellite lesions, corneal perforation, endoexudates, and anterior chamber hypopyon closely resemble fungus. The classical clinical features of Pythium that distinguish it from other microorganisms are reticular dots, tentacular projections, peripheral furrowing, and early limbal spread, which require a high index of clinical suspicion. Pythium also exhibits morphological and microbiological resemblance to fungus on routine smearing, revealing perpendicular or obtuse septate or aseptate branching hyphae. Culture on blood agar or any other nutritional agar is the gold standard for diagnosis. It grows as cream-colored white colonies with zoospores formation, further confirmed using the leaf incarnation method. Due to limited laboratory diagnostic modalities and delayed growth on culture, there was a recent shift toward various molecular diagnostic modalities such as polymerase chain reaction, confocal microscopy, ELISA, and immunodiffusion. As corneal scraping (10% KOH, Gram) reveals fungal hyphae, antifungals are started before the culture results are available. Recent in vitro molecular studies have suggested antibacterials as the first-line drugs in the form of 0.2% linezolid and 1% azithromycin. Early therapeutic keratoplasty is warranted in nonresolving cases. This review aims to describe the epidemiology, clinical features, laboratory and molecular diagnosis, and treatment of Pythium insidiosum keratitis.

Global Distribution and Clinical Features of Pythiosis in Humans and Animals

Pythiosis is a difficult-to-treat infectious disease caused by Pythium insidiosum. The condition is unfamiliar among healthcare workers. Manifestation of pythiosis is similar to other fungal infections, leading to misdiagnosis and delayed treatment. The geographical extent of pythiosis at a global scale is unclear. This study aimed to analyze the clinical information recorded in the scientific literature to comprehensively project epidemiological characteristics, clinical features, and future trends of pythiosis. From 1980 to 2021, 4203 cases of pythiosis in humans (n = 771; 18.3%) and animals (primarily horse, dog, and cow; n = 3432; 81.7%), with an average of 103 cases/year, were recruited. Pythiosis case reports significantly increased in the last decade. Pythiosis spanned 23 tropical, subtropical, and temperate countries worldwide. Some patients acquired pythiosis from a trip to an endemic country. Strikingly, 94.3% of human cases were in India and Thailand, while 79.2% of affected animals were in the U.S.A. and Brazil. Clinical features of pythiosis varied. Vascular and ocular pythiosis were only observed in humans, whereas cutaneous/subcutaneous and gastrointestinal infections were predominant in animals. Mortality depended on host species and clinical forms: for example, none in patients with ocular pythiosis, 0.7% in cows with a cutaneous lesion, 26.8% in humans with vascular disease, 86.4% in dogs with gastrointestinal pathology, and 100% in several animals with disseminated infection. In summary, this study reports up-to-date epidemiological and clinical features of pythiosis in humans and animals. It increases awareness of this life-threatening disease, as the illness or outbreak can exist in any country, not limited to the endemic areas.

Sensitivity and specificity of potassium hydroxide and calcofluor white stain to differentiate between fungal and Pythium filaments in corneal scrapings from patients of Pythium keratitis

Purpose:

To assess the sensitivity of potassium hydroxide and calcofluor white (KOH+CFW) mount in the diagnosis of Pythium keratitis and concordance among microbiologists.

Methods:

Three microbiologists evaluated the microscopic images of KOH + CFW mounts of confirmed cases of Pythium and fungal keratitis seen between January 2019 and February 2021. The filaments were compared using specific differentiating features. The sensitivity and specificity of KOH + CFW in diagnosing Pythium infection were evaluated along with concordance among the microbiologists.

Results:

Sixty consecutive cases with confirmed growth of fungus or Pythium insidiosum (n = 29) were evaluated. The sensitivity of KOH + CFW in the correct identification of Pythium filaments ranged from 79.3% to 96.5% among three microbiologists. There was good interobserver (k = 0.76–0.90) and intraobserver (k = 0.70–0.97) agreements among three microbiologists. The differentiating findings (P < 0.0001) suggestive of Pythium filaments were the absence of septae in 23 (79.3%) and collapsed walls in 22 (75.9%) cases.

Conclusion:

KOH + CFW has good sensitivity and specificity in the diagnosis of Pythium keratitis with good interobserver and intraobserver concordance.

History and Perspective of Immunotherapy for Pythiosis

The fungus-like microorganism Pythium insidiosum causes pythiosis, a life-threatening infectious disease increasingly reported worldwide. Antimicrobial drugs are ineffective. Radical surgery is an essential treatment. Pythiosis can resume post-surgically. Immunotherapy using P. insidiosum antigens (PIA) has emerged as an alternative treatment. This review aims at providing up-to-date information of the immunotherapeutic PIA, with the focus on its history, preparation, clinical application, outcome, mechanism, and recent advances, in order to promote the proper use and future development of this treatment modality. P. insidiosum crude extract is the primary source of immunotherapeutic antigens. Based on 967 documented human and animal (mainly horses) pythiosis cases, PIA immunotherapy reduced disease morbidity and mortality. Concerning clinical outcomes, 19.4% of PIA-immunized human patients succumbed to vascular pythiosis instead of 41.0% in unimmunized cases. PIA immunotherapy may not provide an advantage in a local P. insidiosum infection of the eye. Both PIA-immunized and unimmunized horses with pythiosis showed a similar survival rate of ~70%; however, demands for surgical intervention were much lesser in the immunized cases (22.8% vs. 75.2%). The proposed PIA action involves switching the non-protective T-helper-2 to protective T-helper-1 mediated immunity. By exploring the available P. insidiosum genome data, synthetic peptides, recombinant proteins, and nucleic acids are potential sources of the immunotherapeutic antigens worth investigating. The PIA therapeutic property needs improvement for a better prognosis of pythiosis patients.

Retrospective multifactorial analysis of Pythium keratitis and review of literature

Purpose:

The aim of this work was to study the demographic profile, clinical diagnostic features, challenges in management, treatment outcomes, and ocular morbidity of microbiological culture-proven Pythium keratitis in a tertiary eye care hospital in South India.

Methods:

Retrospective analysis of microbiologically proven Pythium keratitis patients was performed at a tertiary eye center from October 2017 to March 2020. Demographic details, risk factors, microbiological investigations, clinical course, and visual outcomes were analyzed.

Results:

Thirty patients were analyzed. The mean age was 43.1±17.2 years. Most common risk factors were history of injury in 80% and exposure to dirty water in 23.3%. Visual acuity at baseline was 20/30 to perception of light (PL). The most common clinical presentation was stromal infiltrate and hypopyon in 14 (46.6%) patients each. The microbiological confirmation was based on culture on blood agar and vesicles with zoospores formation with incubated leaf carnation method. Seven (23.3%) patients improved with topical 0.2% Linezolid and topical 1% Azithromycin, 19 (63.3%) patients underwent Therapeutic keratoplasty (TPK) and 4 were lost to follow-up. Seven (23.3%) patients had graft reinfection, and 3 (10%) developed endophthalmitis. The final visual acuity was 20/20- 20/200 in 6 (20%) patients, 20/240-20/1200 in 5 (16.6%) patients, hand movement to positive perception of light in 16 patients and no perception of light (Pthisis Bulbi) in 3 (10%) patients.

Conclusion:

P. insidiosum keratitis is a rapidly progressive infectious keratitis with prolonged and relapsing clinical course. It usually results in irreparable vision loss in majority of the patients. Prompt diagnosis, clinical awareness, and specific treatment options are needed for successfully managing this devastating corneal disease.