Renaissance of an Emerging Pathogen-Pythium insidiosum Keratitis: An Indian Perspective

Pythium insidiosum keratitis is an aggressive, vision-threatening corneal infection increasingly recognized across India, particularly among agricultural workers during monsoon season. Frequently misclassified as fungal keratitis, it responds poorly to conventional antifungals because the oomycete has a cellulose- and β-glucan-rich wall and lacks ergosterol, leading to therapeutic delay and rapid stromal melt. Indian cohorts have refined a practical diagnostic signature such as tentacular or reticular peripheral infiltrates with guttering, early endothelial plaque and hypopyon, and minimal satellite lesions. Calcofluor white and KOH show broad, ribbon-like, sparsely septate filaments; blood agar often grows colonies while Sabouraud shows scant growth; IVCM reveals thin, linear, right-angle branching hyphae; and PCR/ITS sequencing confirms species. Emerging immunology indicates early evasion of pattern-recognition receptors (TLR/CLR pathways) followed by dysregulated neutrophilic inflammation that accelerates collagenolysis. Management in India has converged on a surgery-first bias for deep or progressive disease early therapeutic keratoplasty with wide margins combined with targeted medical therapy: topical linezolid 0.2% and azithromycin 1% (± minocycline systemically), aggressive lubrication, and stromal melt mitigation (oral doxycycline, cautious steroids only post-control). Adjuncts include cyanoacrylate for impending perforation and intracameral/ intrastromal antibiotics in selected cases. Outcomes improve with rapid organism-specific therapy, meticulous peri-operative planning, and vigilant recurrence surveillance. India's experience underscores priorities for the next decade: point-of-care diagnostics (LAMP/CRISPR), standardized drug susceptibility platforms, optimized peri-keratoplasty protocols, and host-directed immunomodulation to temper destructive inflammation without impairing clearance. This review synthesizes epidemiology, clinical diagnostics, immunopathogenesis, and management, translating India-derived insights into a pragmatic framework for regions confronting the global spread of Pythium keratitis.