First Molecular Confirmation of Canine Ocular Thelaziosis Caused by Thelazia callipaeda From India.

Abstract

OBJECTIVE: To confirm and characterize Thelazia callipaeda infection in a dog using morphological and molecular tools, analyze its phylogenetic relationship with isolates from other regions, and evaluate the clinical and therapeutic outcomes. ANIMALS STUDIED: An 8-year-old male mixed-breed dog with a 2-week history of unilateral mucopurulent discharge, epiphora, conjunctivitis, and corneal ulceration in the right eye. PROCEDURES: Ophthalmic examination revealed multiple thread-like worms in the affected eye. Worms were preserved in 70% ethanol, and genomic DNA was extracted for molecular analysis. A 689 base pair fragment of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene was amplified via polymerase chain reaction, sequenced, and analyzed using Basic Local Alignment Search Tool and Molecular Evolutionary Genetics Analysis (Maximum Likelihood method, 1000 bootstrap replicates) software. Therapeutic management included mechanical removal, systemic ivermectin, and supportive topical therapy, with follow-ups until recovery. RESULTS: The dog exhibited ocular irritation, lacrimation, and conjunctival hyperemia. Morphological features confirmed T. callipaeda (distinct buccal capsule, cuticular striations, and encysted larvae in the anterior end of the female worm). The cox1 gene sequence showed 99.4% similarity with isolates from Slovakia and China, with nucleotide substitutions at positions 298 (Cysteine→Threonine), 339 (Alanine→Glycine), 342 (Threonine→Cysteine), and 348 (Glycine→Alanine). Phylogenetic analysis clustered the isolate with European and Asian lineages. CONCLUSION: This report describes the first molecularly confirmed report of T. callipaeda infection from India, emphasizing the need for increased awareness and regional surveillance of this emerging zoonotic parasite.