An Overview of Parasite Diversity
Eric S. Loker, Bruce V. Hofkin in Parasitology, 2023
Stramenopiles are part of the SAR (Stramenopila-Alveolata-Rhizaria) lineage shown in Figure 2.7. Stramenopiles are also called heterokonts because in many, their motile stages produce flagella of two different shapes. Members of this group, dominated by diatoms, golden algae and brown algae, are largely free-living, but some parasitic lineages occur, most prominent among them the water molds or oomycetes (see also Figure 2.33), including the notorious Phytophthora infestans, cause of the blight responsible for the infamous Irish potato famine. Members of the oomycete genus Pythium frequently cause serious plant diseases and at least one species, P. insidiosum, can infect dogs, domestic animals and people.
Argentinian Wild Plants as Controllers of Fruits Phytopathogenic Fungi
Mahendra Rai, Shandesh Bhattarai, Chistiane M. Feitosa in Wild Plants, 2020
The Brassicaceae family plays an important role in human nutrition and has several representatives in the Argentine flora (Jahangir et al. 2009). One of them is Rapistrum rugosum “nabo”, an annual herb with glabrous or pubescent ellipsoid fruit that allow distinguishing it easily in the field (Figures 6.4g and h). The family which it belongs to is recognized for the production of glucosinolates (Holtz and Williamson 2004). These metabolites are responsible for the biocidal activity reported by several authors (Dubuis et al. 2005). Lazzeri and Mancini (2001), simulating this species as green manure, suppressed Pythium sp., and also induced an increase in total soil microbial activity.
Linezolid
M. Lindsay Grayson, Sara E. Cosgrove, Suzanne M. Crowe, M. Lindsay Grayson, William Hope, James S. McCarthy, John Mills, Johan W. Mouton, David L. Paterson in Kucers’ The Use of Antibiotics, 2017
Pythium insidiosum, the main human pathogen of the fungus-like oomycetes, has proven difficult to treat with antifungal therapy because it does not produce ergosterol, the main target of these drugs. Loreto et al. (2014) therefore tested the activity of a number of antibacterial drugs against Pythium in vitro and found linezolid to be active with an MIC90 of 4 mg/l (range 1–8 mg/l) using Etest, and 32 mg/l (4–32 mg/l) at 48 hours. Further work is required to resolve this discrepancy between methods.
Unusual Presentation of Pythium Keratitis as Peripheral Ulcerative Keratitis: Clinical Dilemma
Published in Ocular Immunology and Inflammation, 2022
Anahita Kate, Bhupesh Bagga, Lalit K. Ahirwar, Dilip K. Mishra, Savitri Sharma
After 1 week of instituting anti-Pythium therapy, topical corticosteroids (1% prednisolone acetate) were started four times per day. However, despite being on corticosteroids, the anterior chamber reaction increased over the next week. B scan ultrasonography also revealed increasing echoes. Based on the suspicion of residual Pythium infection, diagnostic AC tap and vitreous sample were taken along with injection of 0.1 ml intravitreal linezolid 0.2%. There was no evidence of Pythium infection in both samples; patient was closely followed up and treated with topical linezolid 0.2% for 1.5 months. Topical steroids were gradually tapered and graft failure without any recurrence of infection was noted 4 months after the primary surgery. The patient subsequently underwent an optical keratoplasty for visual rehabilitation and currently has a clear graft with no residual infection.
Pythium insidiosum keratitis: Review of literature of 5 years’ clinical experience at a tertiary eye care center
Published in Seminars in Ophthalmology, 2023
Pratima Vishwakarma, Bhupesh Bagga
Pythium is a plant pathogen commonly found in aquatic ecosystems. It causes pythiosis in mammals including dogs, cats, sheep, horses, and humans.9 In humans, its systemic manifestations include 1) granulomatous ulcers from subcutaneous infections and 2) systemic dissemination of infection with multi-organ involvement and inflammation of arteries with subsequent necrotizing arteritis with thrombosis, aneurysms, gangrene, and aortic leakage resulting in death.6 Risk factors for the systemic disease include thalassemia and contact with water.14
Clinical and Histopathological Evaluation of a Rabbit Model for Pythium insidiosum Keratitis
Published in Current Eye Research, 2020
Paavan Kalra, Lalit Kishore Ahirwar, Ruchi Mittal, Konduri Ranjith, Shilpa Das, Kodiganti Manjulatha, Bhupesh Bagga, Ashik Mohamed, Joveeta Joseph, Savitri Sharma
Keratitis by Pythium insidiosum is a challenging condition to manage and poses a significant threat to vision as well as integrity of the eye as a whole. Pythium, an oomycte, morphologically develops mycelium, and thus resembles fungus. In vivo confocal microscopy of the cornea in patients with culture or polymerase chain reaction positive P. insidiosum keratitis showed that the filaments could not be differentiated from other fungal filaments.1 In an earlier publication we have described the subtle morphological features in the microscopic examination of the corneal scrapings.2 However, these findings can be easily overlooked leading to its misdiagnosis as fungal keratitis. The challenge to its identification is further compounded by its lack of sporulation on routine fungal culture media. Zoospore demonstration of the culture isolates, special stains like iodine-potassium iodide-sulfuric acid, nested polymerase chain reaction and availability of DNA sequencing methods have improved the identification of P. insidiosum and have resulted in increasing number of Pythium keratitis reports, albeit with poor treatment outcome.3–6 Poor outcomes with conventional antifungal treatment are expected as it is biochemically and physiologically very distinct from fungus.7Working towards finding optimum treatment, our in vitro study indicated promising results with antibiotics such as linezolid, azithromycin, tigecycline, mupirocin etc.8 We showed beneficial effect of treatment with a combination of linezolid and azithromycin in a pilot group of culture positive P. insidiosum keratitis patients. Although not significant statistically, the rate of therapeutic penetrating keratoplasty was lower in patients treated with antibacterial antibiotics compared to patients receiving antifungal therapy. Jesus et al showed azithromycin alone or in combination with minocycline to be effective in vivo (rabbit subcutaneous infection model).9 With our foregoing experience, we believe that use of these antibiotics requires further investigation before they can be recommended as definite line of therapy for Pythium keratitis. Aware that the task could be hastened by the availability of an animal model, as a first step, we aimed to develop a model of corneal infection by P. insidiosum in rabbits. In this communication, we report the route of infection, and the clinical characteristics and histopathological changes in the rabbit cornea, following the challenge.
Related Knowledge Centers
- Animal
- Parasitism
- Pythiosis
- Selective Breeding
- Pathogen
- Pythium Insidiosum
- Coenocyte
- Septum
- Oospore
- Plant Disease Resistance