Geographic variation in the elicitin-like glycoprotein, ELI025, of Pythium insidiosum isolated from human and animal subjects

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.

Genotyping and phylogenetic analysis of Pythium insidiosum causing human corneal ulcer

Pythium insidiosum belongs to the Oomycetes, which are known to cause serious life-threatening infectious condition in humans and animals. Corneal infections caused by P. insidiosum are rare and difficult to treat. The molecular-based diagnosis of Pythium is employed for the species identification and to study molecular phylogenetic relationship. Based on Cytochrome oxidase II (cox II) gene, P. insidiosum is categorized into three clades or groups: Clade-I or ATH (American strains), Clade-II or BTH (American, Asian, and Australian strains), and Clade-III or CTH (mostly Thailand strains). This study focused on the molecular identification of Pythium insidiosum from patients with corneal ulcer using ITS regions and clade identification by cox II gene sequencing and correlated with the clinical outcome. The isolates were collected from Aravind Eye Hospital, Madurai, India, from April to December 2018. Through the microbiological laboratory reports, 15 isolates of Pythium sp. from keratitis patient were selected, followed by DNA extraction, ITS, and cox II gene sequencing and phylogenetic analysis using the reference sequences from NCBI database. All 15 P. insidiosum isolates were phylogenetically clustered together as a single group and where also placed distantly from other Pythium species (outgroup). Most ocular isolates fell into either clade BTH or clade CTH, and none of our ocular isolates were in clade ATH. Two of the strains were very distinct and did not match any of the clusters indicating different lineages. There was no significant difference between clinical outcome and genotype of P. insidiosum.

Equine pythiosis in Egypt: clinicopathological findings, detection, identification and genotyping of Pythium insidiosum

BACKGROUND

Equine pythiosis is an emerging, devastating disease that is hard to treat. The tumour-like nodular skin masses grow rapidly and the outcome is generally fatal, and thus early diagnosis and intervention are important.

OBJECTIVES

(i) To highlight the clinical, histological and haematological findings in pythiosis, and (ii) to evaluate the efficacy of direct sample multiplex-PCR targeting the single nucleotide polymorphisms within the ribosomal DNA region for detection and genotyping of Pythium insidiosum.

ANIMALS

Two hundred and twenty horses including 204 Arabian and 16 draft horses were surveyed.

METHODS

Case series study diagnosis was based on clinical, pathological and haematological findings typical of P. insidiosum infection, culture identification, immunohistochemical investigation and direct sample PCR.

RESULTS

The affected horses (24 of 220, 10.91%) presented with unifocal or multiple lesions on the abdomen, limbs, chest, face and mammary gland. Cases commonly had a history of access to stagnant water, ponds and intentionally flooded rice fields. Most were pregnant mares (58.33%). Histopathology revealed granulomatous reaction, blood vessel endotheliosis, heavy infiltration of eosinophils in the dermal layer, multifocal necrosis and Splendore-Hoeppli phenomenon. Unlike direct microscopy (50%) and culture (91.6%), multiplex-PCR assay identified P. insidiosum (Clade II) in all tested samples. To the best of the authors knowledge, this is the first study determining a clade of P. insidiosum causing equine pythiosis in Egypt.

CONCLUSIONS AND CLINICAL IMPORTANCE

Direct sample multiplex-PCR assay is a potential tool for the early and rapid diagnosis of equine pythiosis. It overcomes limitations associated with morphological identification and provides a definitive diagnosis.

Vascular pythiosis of carotid artery with meningitis and cerebral septic emboli: A case report and literature review

Vascular Pythiosis caused by Pythium insiodiosum rarely involves carotid artery. A case of concealed ruptured pseudoaneurysm of the carotid artery with neck abscesses, and cerebral septic emboli is described. Patient presented with large pulsatile neck mass that failed to response to surgery, antifungals and immunotherapeutic vaccine. Residual unresectable disease leads to death in the patient. Pythiosis should be considered as a differential diagnosis of head and neck infection.

Development of an Anti-Elicitin Antibody-Based Immunohistochemical Assay for Diagnosis of Pythiosis

Pythiosis is an emerging and life-threatening infectious disease of humans and animals living in tropical and subtropical countries and is caused by the fungus-like organism Pythium insidiosum. Antifungals are ineffective against this pathogen. Most patients undergo surgical removal of the infected organ, and many die from advanced infections. Early and accurate diagnosis leads to prompt management and promotes better prognosis for affected patients. Immunohistochemical assays (IHCs) have been developed using rabbit antibodies raised against P. insidiosum crude extract, i.e., culture filtrate antigen (CFA), for the histodiagnosis of pythiosis, but cross-reactivity with pathogenic fungi compromises the diagnostic performance of the IHC. Therefore, there is a need to improve detection specificity. Recently, the elicitin protein, ELI025, was identified in P. insidiosum, but it was not identified in other human pathogens, including true fungi. The ELI025-encoding gene was successfully cloned and expressed as a recombinant protein in Escherichia coli. This study aims to develop a new IHC using the rabbit anti-ELI025 antibody (anti-ELI) and to compare its performance with the previously reported anti-CFA-based IHC. Thirty-eight P. insidiosum histological sections stained positive by anti-ELI-based and anti-CFA-based IHCs indicating 100% detection sensitivity for the two assays. The anti-ELI antibody stained negative for all 49 negative-control sections indicating 100% detection specificity. In contrast, the anti-CFA antibody stained positive for one of the 49 negative controls (a slide prepared from Fusarium-infected tissue) indicating 98% detection specificity. In conclusion, the anti-ELI based IHC is sensitive and specific for the histodiagnosis of pythiosis and is an improvement over the anti-CFA-based assay.