Thelaziasis in humans: A systematic review of reported cases

Background: Thelaziasis is an emerging vector-borne zoonotic disease caused by Thelazia spp., which primarily affects animals but is increasingly recognised in humans, where it causes ocular infections. Human thelaziasis remains underreported and poorly understood in many regions despite its growing relevance. Methods: This systematic review analyzed epidemiological, clinical, diagnostic, and therapeutic data from 134 documented human cases of thelaziasis reported across 18 countries. Data sources included peer-reviewed publications and case reports, focusing on identifying trends in geographic distribution, clinical presentation, diagnostic techniques, and treatment approaches. Results: Most cases (82.8%) were reported in Asia, particularly in South Korea, China, India, and Japan. The most common symptoms were foreign body sensation (53%), conjunctival hyperemia (39.6%), and epiphora (33.6%). Infestation was unilateral in 90.3% of cases. Diagnosis was primarily made through direct visual identification of the parasite, while molecular confirmation was used in a limited number of cases. Thelazia callipaeda was the predominant species identified (88.8%). Manual extraction was the mainstay of treatment (88.8%), with antiparasitic agents used in selected instances. Reinfection occurred in 6% of cases. Conclusion: This review underscores the growing recognition of human thelaziasis, particularly in Asia, and highlights the potential underdiagnosis in non-endemic regions. Environmental changes, globalization, and increasing human-animal interactions may facilitate the spread of the disease. Strengthening awareness, surveillance, and control measures is essential. Adopting a One Health approach, integrating human, animal, and environmental health perspectives, is critical for effective prevention and mitigation strategies.