From Asia to Europe: epidemiology, genetic diversity, and One Health implications of Thelazia callipaeda

Thelazia callipaeda, commonly known as the oriental eyeworm, is a vector-borne parasitic nematode that infects the ocular tissues of a wide range of mammalian hosts, including dogs, cats, wildlife, and humans. Historically confined to East and Southeast Asia, T. callipaeda has emerged over the past 2 decades as a significant zoonotic parasite in Europe, with an expanding geographic distribution driven by the spread of lachryphagous drosophilid fruit fly vectors of the genus Phortica. This review synthesizes current knowledge on the taxonomy, epidemiology, biology, genetic diversity, pathogenesis, and control of T. callipaeda, with particular emphasis on its One Health relevance. Molecular studies reveal low but structured genetic variability, characterised by a single predominant haplotype circulating in Europe and high haplotype diversity in Asian populations, reflecting long-term endemicity and distinct transmission dynamics. Clinically, infection can result in ocular irritation ranging from mild conjunctivitis to severe keratitis and corneal ulceration, with dogs acting as the primary domestic reservoir and wildlife sustaining sylvatic transmission cycles. Human infections, though underreported, are increasingly recognised and pose a growing public health concern. Effective management relies on mechanical worm removal, macrocyclic lactone treatment and prevention, and integrated surveillance of animal hosts and vectors. Given the influence of climate change, animal mobility, and environmental factors on vector ecology, coordinated One Health strategies are essential to mitigate the continued spread and zoonotic impact of this emerging eyeworm.