Answer to October 2018 Photo Quiz

Answer: Human thelaziasis. The structures collected from our patient were fixed in 70% ethanol and morphologically identified as Thelazia callipaeda nematodes. The presence of a curled tail end indicated that these were adult males of the species (1). The identification was morphologically confirmed by the Laboratory of Pathogenic Biology, College of Basic Medicine, Wenzhou Medical University, Wenzhou, China. Clinical signs and symptoms were also consistent with human thelaziasis.

Most infections of T. callipaeda involve the conjunctival sac, lacrimal gland, and lacrimal ducts of dogs, cats, and rodents, but the organism occasionally infects humans (2, 3). Because human cases of T. callipaeda infection are most commonly found in Eastern and Southeastern Asia, it is also known as the “Oriental eye worm,” although infections are also found in other geographic areas as well, with over 400 reported cases (4). Extensive experience and research have shown that flies of the order Diptera, Drosophilidae family, genus Phortica, are vectors and transient hosts for this parasite (5). Animal lacrimal secretions containing embryonated eggs or larvae are the putative sources of infection for humans. Thelaziasis occurs most commonly in the summer and autumn, mainly among children and the elderly living in poor rural areas.

Nematodes localized in the eyes of humans can cause presentations which range from asymptomatic to manifestations of mild itchiness, tearing, pain, foreign body sensation, hypersensitivity to light, blurred vision, exudative conjunctivitis, corneal scratches, serious clouding and scarring of the conjunctiva and cornea, corneal ulceration, and keratitis. Generally, thelaziasis does not require any special treatment other than removal of the nematodes. The more severe symptoms usually occur when effective treatment does not occur. The larvae can also penetrate into the subconjunctival space and vitreous cavity, although that is unusual (6). T. callipaeda rarely causes inner eye infections; consequently, symptomatic treatment, including foreign body removal and antimicrobial eye drops or ointment prescribed for ≈7 days, is generally effective (2). In our case, the patient had only mild itchiness and redness following nematode removal. Chloramphenicol eye drops were prescribed (three times a day for 7 days), and all ocular symptoms rapidly resolved.

In this report, although the patient lived in an urban rather than a rural area, he had a history of contact with dogs during his work as a delivery man. We can only speculate that the mode of transmission in this case was contamination of his hands with eggs/larvae of T. callipaeda and subsequent transfer to his right eye.

See https://doi.org/10.1128/JCM.00376-17 in this issue for photo quiz case presentation.