Abstract

Pythium is an oomycete of Phylum Straminopila (green algae), Class Oomycetes, Order Pythiales and Family Pythiaceae that causes a devastating infection of the cornea but was first associated with various systemic infections. It lacks ergosterol in the cytoplasmic membrane and doesn’t have chitin in the cell wall like fungus; instead contains beta glucans and cellulose. This article we are reviewing about brief taxonomy with various investigation and management of pythium keratitis till date. Risk factors include dust, foreign body, vegetative matter, dirty water, insect injury, idiopathic, improper previous treatment with prolonged non-compliance. Common signs observed are tentacle like infiltrate, hypopyon, endothelial exudates, dot like infiltrate, superficial plaque, total corneal ulcer, peripheral furrowing and perforated corneal ulcer. Microbiological examination helps to establish a definitive diagnosis with corneal scrapping subjected to 10% KOH wet mount, Gram stain, Potassium iodide-sulfuric acid showing thin septate hyphae and culture with 5% sheep blood agar at 37 degree shows flat, feathery edged, partially submerged, colourless colonies. Polymerase chain reaction (PCR) with DNA sequencing is very useful diagnostic method showing vesicles with zoospores which develop after incubation just before zoospore release. Confocal microscopy shows presence of hyperreflective, double-walled filaments varying in size. Histopathological examination is with GMS, PAS and H & E stains. Various new methods have come for diagnosis like proteomic analysis, molecular analysis, Loop medicated isothermal amplification (LAMP). Treatment comprises of medical and surgical intervention. In medical intervention started with topical natamycin, combination of natamycin and voriconazole eyedrops, itraconazole 1% eyedrops, topical linezolid (0.2%) hourly and 1% azithromycin eye ointment twice daily with oral azithromycin 500mg once daily for 2 weeks and minocycline eye ointment 4 times per day, oral linezolid 1200mg twice daily and topical chloramphenicol eyedrops hourly combination. Triple drug regimen with topical (0.2%) and oral linezolid and topical 1% azithromycin eye ointment has showed good outcome. In surgical intervention we have seen either Therapeutic keratoplasty (TPK) either alone or with Nitrous oxide Cryotherapy with alcohol swab. If infection is too aggressive it may require evisceration or enucleation. There were reported cases with immunotherapy with PIA vaccine and topical ethanol showing some improvement but require larger study to comment on its efficacy.