Human Pythiosis: Emergence of Fungal-Like Organism

Ex vivo observation of Pythium insidiosum-antigen treated neutrophils on three Pythium insidiosum strains isolated from vascular pythiosis patients

The mechanisms of Pythium insidiosum-antigen (PIA) immunotherapy activating a patient's immune system are unknown. We evaluated the interleukin-8 (IL-8) serum levels during P. insidiosum infection and after vaccination with PIA in vascular pythiosis cases. Furthermore, we studied the anti-P. insidiosum activity of neutrophils stimulated with various concentrations of PIA ex vivo in 3 strains of P. insidiosum isolated from vascular pythiosis patients. IL-8 serum levels were evaluated using the ELISA technique. We assessed the effect of PIA-stimulated neutrophils on the viability of zoospores using MTT assay, visualized neutrophil extracellular trap (NET) formation via microscopy, and measured the levels of double-stranded DNA (dsDNA) using PicoGreen dsDNA quantitation assay in 3 strains of P. insidiosum isolated from vascular pythiosis patients. Serum levels of IL-8 gradually lowered from the early to the end phases of vaccination with PIA among the surviving group of vascular pythiosis cases. Neutrophils stimulated with 0.01 µg/ml PIA reduced zoospore viability significantly compared to PIA-unstimulated neutrophils for strain 1 and strain 3 (p < .05). Neutrophils stimulated with 0.01, 0.1, 1, and 10 µg/ml PIA exhibited significantly lower zoospore viability than PIA-unstimulated neutrophils for strain 2 (p < .05). IL-8 can be used as a biomarker for monitoring vascular pythiosis cases treated with the PIA vaccine. Also, anti-P. insidiosum activity of PIA-stimulated neutrophils was probably due to the disruption of cellular activity in zoospores rather than the mechanisms based on the formation of NETs.

Potential anti-Pythium insidiosum therapeutics identified through screening of agricultural fungicides

Pythiosis is a life-threatening infectious disease caused by the oomycete Pythium insidiosum. Clinical manifestations of pythiosis include an eye, blood vessel, skin, or gastrointestinal tract infection. Pythiosis has been increasingly reported worldwide, with an overall mortality rate of 28%. Radical surgery is required to save patients' lives due to the limited efficacy of antimicrobial drugs. Effective medical treatments are urgently needed for pythiosis. This study aims to find anti-P. insidiosum agents by screening 17 agricultural fungicides that inhibit plant-pathogenic oomycetes and validating their efficacy and safety. Cyazofamid outperformed other fungicides as it can potently inhibit genetically diverse P. insidiosum isolates while exhibiting minimal cellular toxicities. The calculated therapeutic scores determined that the concentration of cyazofamid causing significant cellular toxicities was eight times greater than the concentration of the drug effectively inhibiting P. insidiosum. Furthermore, other studies showed that cyazofamid exhibits low-to-moderate toxicities in animals. The mechanism of cyazofamid action is likely the inhibition of cytochrome b, an essential component in ATP synthesis. Molecular docking and dynamic analyses depicted a stable binding of cyazofamid to the Qi site of the P. insidiosum's cytochrome b orthologous protein. In conclusion, our search for an effective anti-P. insidiosum drug indicated that cyazofamid is a promising candidate for treating pythiosis. With its high efficacy and low toxicity, cyazofamid is a potential chemical for treating pythiosis, reducing the need for radical surgeries, and improving recovery rates. Our findings could pave the way for the development of new and effective treatments for pythiosis.IMPORTANCEPythiosis is a severe infection caused by Pythium insidiosum. The disease is prevalent in tropical/subtropical regions. This infectious condition is challenging to treat with antifungal drugs and often requires surgical removal of the infected tissue. Pythiosis can be fatal if not treated promptly. There is a need for a new treatment that effectively inhibits P. insidiosum. This study screened 17 agricultural fungicides that target plant-pathogenic oomycetes and found that cyazofamid was the most potent in inhibiting P. insidiosum. Cyazofamid showed low toxicity to mammalian cells and high affinity to the P. insidiosum's cytochrome b, which is involved in energy production. Cyazofamid could be a promising candidate for the treatment of pythiosis, as it could reduce the need for surgery and improve the survival rate of patients. This study provides valuable insights into the biology and drug susceptibility of P. insidiosum and opens new avenues for developing effective therapies for pythiosis.

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.

Atypical microbial keratitis

Atypical microbial keratitis refers to corneal infections caused by micro-organisms not commonly encountered in clinical practice. Unlike infections caused by common bacteria, cases of atypical microbial keratitis are often associated with worse clinical outcomes and visual prognosis. This is due to the challenges in the identification of causative organisms with standard diagnostic techniques, resulting in delays in the initiation of appropriate therapies. Furthermore, due to the comparatively lower incidence of atypical microbial keratitis, there is limited literature on effective management strategies for some of these difficult to manage corneal infections. This review highlights the current management and available evidence of atypical microbial keratitis, focusing on atypical mycobacteria keratitis, nocardia keratitis, achromobacter keratitis, and pythium keratitis. It will also describe the management of two uncommonly encountered conditions, infectious crystalline keratopathy and post-refractive infectious keratitis. This review can be used as a guide for clinicians managing patients with such challenging corneal infections.

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.

Clinical Characteristics and Outcomes of Rare Fungal Keratitis Caused by Verticillium dahliae

PURPOSE

To observe clinical characteristics and treatment outcomes of fungal keratitis caused by Verticillium dahliae.

METHODS

Clinical data of 7 patients diagnosed as fungal keratitis cause by Verticillium dahliae were retrospectively analyzed. The clinical manifestations, mycology, in vitro antifungal susceptibility, treatment regimens and prognoses of the patients were evaluated.

RESULTS

All 7 patients were farm worker, of which 5 cases were caused by plant trauma. The corneal ulcer had a round shape and a relatively limited range with the diameters mainly in the range of 2-7 mm. The stromal infiltration was mild, and had no pseudopodia, mossiness or endothelial plaques. Intact hyphaes were detected in corneal scrapings and confocal microscopy, isolates were identified by morphology and by sequencing the internal transcribed spacer region of ribosomal DNA. In vitro antifungal susceptibility testing showed that the most sensitive antifungal drug was Amphotericin B. In the 6 patients with an ulcer less than 2/3 of the corneal thickness, the ulcer healed after 18 days of antifungal treatment only in one eye. The other five patients underwent corneal ulcer debridement or conjunctival flap covering surgery. The remaining one patient with ulcer depth more than 2/3 of the corneal thickness underwent lamellar keratoplasty.

CONCLUSION

Fungal keratitis caused by Verticillium dahliae has typical signs of a mild inflammatory response, and is not sensitive to antifungal drugs. It is recommended that patients undergo corneal ulcer debridement as soon as possible to promote rapid healing of the ulcers.

Vascular pythiosis caused by Pythium aphanidermatum: the first case report in Asia

BACKGROUND

Pythium, soil-borne plant pathogens, are in the class Oomycetes. They are not true fungi, but are related to diatom and algae. There are two human pathogens including P. insidiosum and P. aphanidermatum. To date, only one case of pythiosis caused by P. aphanidermatum has been reported. We present herein the first case of P. aphanidermatum vascular pythiosis in Asia.

CASE PRESENTATION

A 47-year-old Thai woman, living in North Thailand, with ß thalassemia/hemoglobin E presented with acute recurrent arterial insufficiency of both legs. Emergent embolectomy with clot removal was performed. The pathology of the clot exhibited noncaseous granulomatous inflammation with many fungal hyphal elements. PCR identified P. aphanidermatum with 100% identity. Final diagnosis is vascular pythiosis. Unfortunately, the patient eventually expired after treatment with itraconazole, terbinafine, azithromycin, and doxycycline.

CONCLUSIONS

To date, only one case of pythiosis caused by P. aphanidermatum has been reported. We present herein the first case of P. aphanidermatum vascular pythiosis in Asia.

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.

Approach to the Patient with a Skin and Soft Tissue Infection

The diagnosis of a skin and soft tissue infection (SSTI) requires careful attention to a patient's history, physical examination, and diagnostic test results. We review for many bacterial, viral, fungal, and parasitic pathogens that cause SSTIs the clues for reaching a diagnosis, including reported past medical history, hobbies and behaviors, travel, insect bites, exposure to other people and to animals, environmental exposures to water, soil, or sand, as well as the anatomic site of skin lesions, their morphology on examination, and their evolution over time. Laboratory and radiographic tests are discussed that may be used to confirm a specific diagnosis.

Clinical Outcomes of Radical Surgery and Antimicrobial Agents in Vascular Pythiosis: A Multicenter Prospective Study

Vascular pythiosis is a rare, neglected, life-threatening disease with mortality of 100% in patients with incomplete surgical resection or patients with persistently elevated serum β-d-glucan (BDG). The study was conducted to understand the clinical outcomes of new treatment protocols and potential use of erythrocyte sedimentation rate (ESR) and c-reactive protein (CRP) as alternative monitoring tools, given recent favorable minimum inhibitory concentrations (MICs) of antibacterial agents and prohibitive cost of serum BDG in Thailand. A prospective cohort study of patients with vascular pythiosis was conducted between February 2019 and August 2020. After diagnosis, patients were followed at 0.5, 1, 1.5, 3, and 6 months. Descriptive statistics, Spearman's correlation coefficient, and general linear model for longitudinal data were used. Amongst the cohort of ten vascular pythiosis patients, four had residual disease after surgery. Among four with residual disease, one developed disseminated disease and died, one developed relapse disease requiring surgery, and two were successfully managed with antimicrobial agents. The spearman's correlation coefficients between BDG and ESR, and between BDG and CRP in patients without relapse or disseminated disease were 0.65 and 0.60, respectively. Tetracyclines and macrolides had most favorable minimum inhibitory concentrations and synergistic effects were observed in combinations of these two antibiotic classes. Adjunctive use of azithromycin and doxycycline preliminarily improved survival in vascular pythiosis patients with residual disease. Further studies are needed to understand the trends of ESR and CRP in this population.

A case of canine cutaneous pythiosis in Thailand

Introduction

Pythium insidiosum causes pythiosis in humans and animals in tropical and subtropical climates. The clinical manifestations in humans are mostly systemic, vascular or ocular forms, in contrast to animals, which are cutaneous, subcutaneous and gastrointestinal forms. The highest incidence of human cases is reported in Thailand, however, no canine pythiosis has been documented yet.

Case presentation

A female, mixed-breed, stray dog showed severe extensive ulcerative haemorrhagic dermatitis at the perineum involving the anus and tail. On cytology, there were sparse branching septate fungal hyphae. The tissue samples were subjected to polymerase chain reaction and gene sequencing for fungal identification.

Conclusion

The results of the internal transcribed spacer 1 and 2 (ITS1 and ITS2) gene had 99 % homology to Pythium insidiosum (accession no. FJ17396) and the COX2 gene (accession no. GQ451572). The phylogenetic tree of both genes was classified in clade A_TH. This is the first fully documented diagnosis of canine cutaneous pythiosis in Thailand.