Successful management of pediatric pythium insidiosum keratitis with cyanoacrylate glue, linezolid, and azithromycin: Rare case report

Anti-infective therapies for Pythium insidiosum keratitis

INTRODUCTION

Pythium insidiosum keratitis (PIK) is a rapidly progressing ocular disease predominantly found in tropical and subtropical regions. Characterized by severe corneal damage and high morbidity, this infection poses significant challenges in diagnosis and management, necessitating effective anti-infective therapies.

AREAS COVERED

This report delves into the pathophysiology, clinical and microbiological diagnosis, and detailed insights into the anti-infective therapy for PIK, outlining current diagnostic challenges that complicate treatment. We review existing anti-infective therapies, including their efficacy and limitations, and discuss the role of surgical interventions in managing advanced cases. The report also highlights ongoing research into novel treatment approaches and the critical need for developing targeted therapies.

EXPERT OPINION

Despite advances in understanding PIK, treatment remains complex due to pathogen resistance and diagnostic hurdles. Future research should focus on innovative anti-infective strategies, improved diagnostic techniques, and global surveillance to enhance therapeutic outcomes. Collaboration between ophthalmologists, microbiologists, and pharmacologists is essential to advance treatment protocols and improve patient prognosis.

Pythium insidiosum: an emerging pathogen that is easily misdiagnosed and given treatment as a fungus

Background

Pythium insidiosum (P. insidiosum) is the causative agent of pythiosis, an infectious disease with a high morbidity and fatality rate. Pythiosis cases have increased dramatically during the past ten years, particularly in tropical and subtropical areas. Sadly, microbiologists and medical professionals know very little about pythiosis, and the disease is frequently challenging to identify. It is frequently misdiagnosed as a fungal infection.

Methods

We report two cases of pythiosis, one was Pythium keratitis, the other was cutaneous pythiosis. The patient with corneal infection had no underlying disease, while the patient with cutaneous pythiosis had a history of liver cirrhosis, diabetes, and psoriasis. The corneal sample and subcutaneous pus were sent for metagenomic Next-Generation Sequencing (mNGS). To further diagnose the isolated strain, P. insidiosum zoospores were induced to produce by co-incubation with sterile grass leaves in sterile pond water. Their zoospores were used as an inoculum for drug susceptibility testing by disk diffusion and broth microdilution method.

Results

The mNGS of two cases were reported as P. insidiosum. Zoospores were produced after incubation 48h. The zoospores were collected for drug susceptibility assay. All antifungal drugs, antibacterial drugs of β-Lactams, vancomycin, levofloxacin, ciprofloxacin, gentamicin, trimethoprim-sulfamethoxazole, clindamycin have no inhibitory activity against P. insidiosum in vitro. Minocycline, tigecycline, linezolid, erythromycin and azithromycin have significant in vitro activity against P. insidiosum. Based on the susceptibility results, the drug was changed from itraconazole to linezolid and minocycline, along with multiple debridements and drainage for cutaneous pythiosis. The patient was discharged after 24 days of treatment.

Conclusions

Early and accurate identification, combined with aggressive surgical debridement and appropriate drug therapy, can greatly improve patient managements. Conventional culture and zoospore induction remain gold standard for diagnosis; however, DNA-based method should be performed simultaneously. The drug susceptibility testing provides profound effects on proper drug selection against P. insidiosum.

Outcomes of keratoplasty in a cohort of Pythium insidiosum keratitis cases at a tertiary eye care center in India

PURPOSE

To assess outcomes of keratoplasty performed in patients diagnosed with keratitis caused by Pythium insidiosum (PI).

DESIGN

Retrospective review.

METHODS

Preoperative, intra operative and post operative data of patients diagnosed with PI keratitis and who underwent keratoplasty for their condition from January 2020 to December 2021 were collected from the central patient database of a tertiary eye care hospital in India. The data were analyzed for anatomic success, elimination of infection, graft survival, incidence of repeat keratoplasty, final visual acuity and varied complications.

RESULTS

In total, 16 eyes underwent penetrating keratoplasty for PI keratitis during the study period. Mean time to keratoplasty from onset of symptoms was 31.3 days and mean graft size was 10.4 mm. Nine out of the 16 cases had recurrence of infection following surgery, seven of which required a repeat keratoplasty for elimination of infection. Mean graft size for repeat keratoplasty performed in recurrent cases was 11.7 mm. Globe was successfully salvaged in 14 out of 16 patients (87.5 %). Three grafts remained clear at 6-month follow up while 11 grafts failed. Mean improvement in uncorrected visual acuity from 2.32 to 2.04 logMAR was observed at last follow up. Endo-exudates, graft infiltration, graft dehiscence, secondary glaucoma and retinal detachment were the various complications noted after keratoplasty.

CONCLUSION

PI keratitis is a tenacious and potentially blinding condition. Keratoplasty remains the choice of treatment in this condition, however recurrence of disease and graft failure are common. Large sized grafts, meticulous per-operative removal of infection, adjuvant cryotherapy, and intraoperative and post operative use of antibiotics can help in improving outcome of keratoplasty in these patients.

Successful Management of Pythium insidiosum Keratitis Masquerading as Dematiaceous Fungal Keratitis in an Immunosuppressed Asian Male

PURPOSE

To describe the first case of Pythium insidiosum keratitis masquerading as dematiaceous fungal keratitis in a seropositive male.

CASE SUMMARY

A 44-year-old seropositive male previously treated for acute retinal necrosis presented with pain and defective vision in the right eye following a mud injury 5 days back. Presenting visual acuity was hand movements close to the face. Ocular examination revealed a 7 × 7 mm dense, greyish-white mid stromal infiltrate with pigmentation and few tentacles. The clinical diagnosis suggested fungal keratitis. Corneal scraping on 10% KOH and Gram stain revealed slender, aseptate hyaline hyphae. Before culture results, the patient was treated with topical 5% natamycin and 1% voriconazole, but the infiltrate progressed. Culture on 5% sheep blood agar revealed white fluffy, submerged, shiny, and appressed colonies, and Pythium insidiosum was confirmed by zoospore formation. The patient was further managed with topical linezolid 0.2% hourly, azithromycin 1% hourly, and adjuvant drugs.

CONCLUSION

This is an uncommon presentation of Pythium keratitis masquerading as dematiaceous fungal keratitis in an immunocompromised male.

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.

Pythium insidiosum: In vitro oomicidal evaluation of telithromycin and interactions with azithromycin and amorolfine hydrochloride

This study evaluated the repositioning of the ketolide antibacterial telithromycin (TLT) against the oomycete Pythium insidiosum and verified the combination of TLT and the antimicrobials azithromycin (AZM) and amorolfine hydrochloride (AMR), which have known anti-P. insidiosum activity. Susceptibility tests of P. insidiosum isolates (n = 20) against the drugs were carried out according to CLSI protocol M38-A2, and their combinations were evaluated using the checkerboard microdilution method. The minimum inhibitory concentrations were 0.5-4 µg/mL for TLT, 2-32 µg/mL for AZM, and 16-64 µg/mL for AMR. For the TLT+AZM combination, 52.75 % of interactions were indifferent, 43.44 % were antagonistic, and 9.70 % were synergistic. As for interactions of the TLT+AMR combination, 60.43 % were indifferent, 39.12 % were antagonistic, and 10.44 % synergistic interactions. This study is the first to evaluate the repositioning of the antibacterial TLT against mammalian pathogenic oomycetes, and our results show that its isolated action is superior to its combinations with either AZM or AMR. Therefore, we recommend including TLT in future research to evaluate therapeutic approaches in different clinical forms of human and animal pythiosis.

Understanding barriers, recommended solutions, and future prospects for the diagnosis and management of Pythium insidiosum keratitis

Pythium insidiosum keratitis (PIK) is a devastating corneal infection resulting in blindness in a large number of cases. Clinically and morphologically, it closely mimics fungal keratitis, and hence is also labeled as "parafungus." Although many clinical studies have documented evidence regarding the virulence of microorganism, and anatomical and functional outcomes, it remains a clinical challenge and diagnostic dilemma for most clinicians. Till today, PIK is being diagnosed and treated with certainty at only limited centers across the globe. But the question is why this is so? Taking this as the research question, this section on current ophthalmology aims to highlight the understanding of barriers to diagnosing and treating PIK, the suggestions to improve diagnosis and treatment, and the future prospects.

Predicting Prognosis Based on Regional Prevalence, Ulcer Morphology and Treatment Strategy in Vision-Threatening Pythium insidiosum Keratitis

Pythium insidiosum is an oomycete belonging to the phylum Straminipila and family Pythiaceae. It causes rapidly progressive vision-threatening keratitis. Clinically, microbiologically and morphologically, it closely resembles fungal keratitis; hence it is also labelled as a "parafungus". The clinical features mimicking fungus are subepithelial and stromal infiltrate, endo-exudates, corneal melt and hypopyon. The hallmark features of Pythium are tentacular projections, reticular dot-like infiltrate, peripheral furrowing and thinning, and rapid limbal spread. Microbiological corneal smearing on KOH and Gram stain reveal septate or aseptate, obtuse to perpendicular hyphae which mimic fungal hyphae. Culture on any nutritional agar reveals cream, cottonwool-like, fluffy colonies, and diagnosis is confirmed by zoospore formation by the leaf incarnation method. Medical management with antifungals and antibacterials still presents a dilemma. Early therapeutic keratoplasty has been the proposed treatment in most cases. We hypothesize that the prognosis of Pythium keratitis is governed by regional geographical variations, ulcer size and density on presentation, and initial treatment strategy. The available literature supporting the proposed hypothesis is also discussed, along with the hallmark features of Pythium and how it masquerades as other microorganisms causing keratitis. We also aim to propose a novel diagnostic and treatment algorithm for managing this vision-threatening keratitis.

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 - 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.

A Review: Antimicrobial Therapy for Human Pythiosis

Human pythiosis is associated with poor prognosis with significant mortality caused by Pythium insidiosum. Antimicrobials’ in vitro and in vivo results against P. insidiosum are inconsistent. Although antimicrobials are clinically useful, they are not likely to achieve therapeutic success alone without surgery and immunotherapy. New therapeutic options are therefore needed. This non-exhaustive review discusses the rationale antimicrobial therapy, minimum inhibitory concentrations, and efficacy of antibacterial and antifungal agents against P. insidiosum. This review further provides insight into the immunomodulating effects of antimicrobials that can enhance the immune response to infections. Current data support using antimicrobial combination therapy for the pharmacotherapeutic management of human pythiosis. Also, the success or failure of antimicrobial treatment in human pythiosis might depend on the immunomodulatory effects of drugs. The repurposing of existing drugs is a safe strategy for anti-P. insidiosum drug discovery. To improve patient outcomes in pythiosis, we suggest further research and a deeper understanding of P. insidiosum virulence factors, host immune response, and host immune system modification by antimicrobials.

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.

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.