Study: Thelazia callipaeda infection in a 41-year-old female patient

Author(s):

Key Takeaways

Thelaziasis is a zoonotic ocular infection caused by Thelazia callipaeda, transmitted by Drosophilid flies, leading to symptoms from mild irritation to severe inflammation.
Diagnosis requires meticulous clinical examination, history-taking, and confirmation through genetic or microscopic testing, especially in patients with exposure risk factors.
Treatment involves mechanical worm removal, conjunctival sac irrigation, and antibiotics, with follow-up to ensure resolution and prevent recurrence.
Preventive strategies include public health education, environmental controls, and regular veterinary screening to manage and prevent Thelazia callipaeda infections.

A team of researchers in China detail a case of Thelazia callipaeda infection in the right eye of a 41-year-old woman working in an office. The patient presented with persistent foreign body sensation, pruritus, and redness despite initial treatment with polyethylene glycol and levofloxacin eye drops.

(Image credit: Adobe Stock/lalandrew)

Thelaziasis, an ocular parasitic infection caused by Thelazia callipaeda, poses unique diagnostic and therapeutic challenges for ophthalmologists.

This zoonotic disease, transmitted by Drosophilid flies, is associated with a spectrum of ocular symptoms ranging from mild irritation to severe inflammation. Here, we present a case of Thelazia callipaeda infection in a 41-year-old woman, followed by a review of the literature to highlight diagnostic, therapeutic, and preventive strategies.¹

Case presentation

In July 2022, a 41-year-old woman sought treatment at Peking University Third Hospital for a foreign body sensation in her right eye. A slit-lamp examination revealed corneal epithelial damage but no visible foreign body. The patient was prescribed polyethylene glycol and levofloxacin eye drops, yet her symptoms persisted.

By August, the patient reported increased itching, redness, and persistent foreign body sensation. Further examination uncovered severe conjunctival congestion and papillary hyperplasia with a pseudomembrane. Using an eyelid retractor, four white linear worms were identified and extracted from the conjunctival sac. Laboratory analysis confirmed the species as Thelazia callipaeda, commonly known as the "oriental eyeworm."

The patient’s medical history revealed seasonal allergies, hyperthyroidism, and pet ownership, including an American Shorthair cat with an unexamined ocular condition. Post-extraction treatment with gatifloxacin eye gel resulted in significant symptomatic relief, with no recurrence over two months.

Epidemiology and pathogenesis

Thelazia callipaeda infections are primarily reported in Asia, Eastern and Southern Europe, and North America. The parasite's life cycle involves intermediate hosts (Drosophilid flies) that transfer infective larvae to definitive hosts during feeding on ocular secretions. Humans, domestic animals (dogs and cats), and wild carnivores serve as definitive hosts.

Thelazia are a group of nematodes and veterinary parasites that can occasionally infect humans, called a zoonotic infection, according to the Centers for Disease Control and Prevention.²

The parasite larvae are typically ingested by a flying insect where inside they grow to full size, and then are spread to animals like dogs, cats, livestock and in some cases, humans, the CDC says. Just like in people, the parasite can cause an eye infection in animals, and humans who regularly interact with animals, particularly in rural communities, can sometimes contract the parasite that way, according to the CDC.

China, which accounts for the highest number of reported thelaziasis cases globally, has documented 86 human cases between 2014 and 2023. Key risk factors include rural residency, animal husbandry, and exposure to flies. The parasite typically causes unilateral infections, with common symptoms including foreign body sensation, itching, and conjunctivitis.

Clinical features and diagnosis

The presented case underscores the importance of meticulous clinical examination in patients with persistent ocular symptoms.

Key diagnostic clues include:

A history of pet ownership or fly exposure.
Observation of worms in the conjunctival sac under slit-lamp examination.
Confirmation via genetic testing or microscopic identification of adult worms.

Treatment

Management involves mechanical removal of worms, conjunctival sac irrigation, and antibiotic treatment to address secondary bacterial infections. Post-treatment follow-up is essential to ensure complete resolution and prevent recurrence.

Preventive measures include:

Public Health Education: Raising awareness about the transmission vectors (flies) and the importance of personal and pet hygiene.
Environmental Controls: Waste management and insect repellent use to curb fly populations.
Veterinary Screening: Regular check-ups for pets to identify and treat infections early.

For ophthalmologists, this case highlights the need to consider Thelazia callipaeda in the differential diagnosis of unexplained ocular symptoms, particularly in patients with exposure risk factors. Detailed history-taking, including allergy, pet ownership, and environmental hygiene, is critical. Thorough slit-lamp examination and, when warranted, genetic or microscopic testing can ensure accurate diagnosis and timely intervention.1

Conclusion

The presented case illustrates the clinical, diagnostic, and therapeutic challenges posed by Thelazia callipaeda infections. By maintaining a high index of suspicion and implementing a multidisciplinary approach that includes public health measures, ophthalmologists can effectively manage and prevent this zoonotic threat.

“Managing and controlling infections caused by Thelazia callipaeda requires a comprehensive approach,” the researchers concluded. “Key measures include enhancing public health education to raise awareness of transmission vectors, such as Drosophilid flies, and promoting hygiene practices.”