Genotyping and phylogenetic analysis of Pythium insidiosum causing human corneal ulcer

Highly sensitive multiplex PCR for convenient quantification and differentiation of canine Oomycota pathogens: Pythium insidiosum, Lagenidium giganteum f. caninum, and Paralagenidium karlingii

Oomycota mammalian pathogens, including Pythium (P.) insidiosum, Lagenidium (L.) giganteum f. caninum, and Paralagenidium (Para.) karlingii, are increasingly recognized as causes of life-threatening infections in dogs, with diagnosis complicated by their clinical and phenotypic resemblance to fungal pathogens. Traditional diagnostic methods, such as serology, histopathology, and culture, often lack sensitivity and specificity, delaying appropriate management. Here, we developed a multiplex PCR assay with remarkable sensitivity, detecting as few as one DNA copy per reaction for P. insidiosum and Para. karlingii and 10 copies per reaction for L. giganteum. Validation on pure isolates from ATCC and USDA-ARS and other clinical isolates confirmed the assay's specificity, correctly identifying all three pathogens and showing no cross-reactivity in non-target isolates. Interestingly, the developed multiplex Oomycota PCR revealed that 45.5% (40/88) of serum samples positive for anti-Pythium antibody contained Pythium DNA. Additionally, among 24 suspected anti-Pythium antibody-positive samples, 54.2% (13/24) tested positive for Pythium DNA, while 8.3% (2/24) contained Lagenidium DNA. By allowing simultaneous detection and differentiation of these pathogens in a single reaction, the multiplex PCR significantly reduces diagnostic time and resource requirements. This highly sensitive diagnostic tool holds promise for enhancing the speed and accuracy of Oomycota infection diagnosis in dogs, as well as other mammalian species, including humans. This could enable the prompt implementation of species-specific diagnosis followed by early intervention, ultimately resulting in improved clinical outcomes.IMPORTANCEThis study addresses a critical gap in the diagnosis of life-threatening infections caused by Oomycota pathogens-Pythium insidiosum, Lagenidium giganteum f. caninum, and Paralagenidium karlingii-in dogs. These pathogens, often misdiagnosed as fungal infections due to overlapping clinical and phenotypic features, require accurate differentiation for appropriate treatment. Current diagnostic methods, including serology, histopathology, and culture, are time-consuming, lack specificity, and are prone to inconclusive results. The newly developed multiplex PCR assay offers a transformative solution by enabling simultaneous detection and differentiation of these pathogens with remarkable sensitivity and specificity. This tool not only reduces diagnostic time but also enhances the accuracy of pathogen identification, paving the way for earlier intervention and improved clinical outcomes. Moreover, its potential application in other mammalian species, including humans, underscores its broader significance in managing Oomycota infections.

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.

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.

Identification and Biotyping of Pythium insidiosum Isolated from Urban and Rural Areas of Thailand by Multiplex PCR, DNA Barcode, and Proteomic Analyses

Pythium insidiosum causes pythiosis, a fatal infectious disease of humans and animals worldwide. Prompt diagnosis and treatment are essential to improve the clinical outcome of pythiosis. Diagnosis of P. insidiosum relies on immunological, molecular, and proteomic assays. The main treatment of pythiosis aims to surgically remove all affected tissue to prevent recurrent infection. Due to the marked increase in case reports, pythiosis has become a public health concern. Thailand is an endemic area of human pythiosis. To obtain a complete picture of how the pathogen circulates in the environment, we surveyed the presence of P. insidiosum in urban (Bangkok) and rural areas of Thailand. We employed the hair-baiting technique to screen for P. insidiosum in 500 water samples. Twenty-seven culture-positive samples were identified as P. insidiosum by multiplex PCR, multi-DNA barcode (rDNA, cox1, cox2), and mass spectrometric analyses. These environmental strains of P. insidiosum fell into Clade-II and -III genotypes and exhibited a close phylogenetic/proteomic relationship with Thai clinical strains. Biodiversity of the environmental strains also existed in a local habitat. In conclusion, P. insidiosum is widespread in Thailand. A better understanding of the ecological niche of P. insidiosum could lead to the effective prevention and control of this pathogen.

Recent update in diagnosis and treatment of human pythiosis

Human pythiosis is an infectious condition with high morbidity and mortality. The causative agent is the oomycete microorganism Pythium insidiosum. The pathogen inhabits ubiquitously in a wet environment, and direct exposure to the pathogen initiates the infection. Most patients with pythiosis require surgical removal of the affected organ, and many patients die from the disease. Awareness of pythiosis among healthcare personnel is increasing. In this review, we summarized and updated information on the diagnosis and treatment of human pythiosis. Vascular and ocular pythiosis are common clinical manifestations. Recognition of the typical clinical features of pythiosis is essential for early diagnosis. The definitive diagnosis of the disease requires laboratory testing, such as microbiological, serological, molecular, and proteomic assays. In vascular pythiosis, surgical intervention to achieve the organism-free margin of the affected tissue, in combination with the use of antifungal drugs and P. insidiosum immunotherapy, remains the recommended treatment. Ocular pythiosis is a serious condition and earliest therapeutic penetrating keratoplasty with wide surgical margin is the mainstay treatment. Thorough clinical assessment is essential in all patients to evaluate the treatment response and detect an early sign of the disease recurrence. In conclusion, early diagnosis and proper management are the keys to an optimal outcome of the patients with pythiosis.