Case 279 -- A Case of Thelazia Californiensis Conjunctival Infestation in Human

Contributed by Yan Peng MD, PhD., Regis Kowalski MS, Lynne, S Garcia* MS, and William Pasculle ScD
    *LSG & Associates, 512 - 12th St., Santa Monica, CA 90402-2908

Published on line in August 2001

A specimen was brought to the Microbiology laboratory of Presbyterian hospital of University of Pittsburgh medical center from a patient's eye.

The eyeworm, Thelazia californiensis is a spiruroid nematode. It was first described by Price in 1930, as a parasite of dogs in the western United States. T. Californiensis can infest dog, cat, sheep, deer and other mammals and causes a disease known as thelaziasis. This is not a common disease. This eyeworm commonly parasitizes in the tear ducts and conjunctival sac of its hosts, and appears as a creamy, thin-white thread measuring slightly over a half an inch in length. The adult worms may be found in the conjunctival sac or tear ducts. The eggs or larvae can be seen when the tears or secretions are examined under the microscope. The eyeworms are most common on the Pacific Coast. Human can become infested, but is extremely rare and thought to be accidental. There are only few reports of Thelazia californiensis infestation in humans.

How do eyeworms reproduce and how are they spread? The adult female worm lays her eggs in the tears. There they develop into larvae that are ingested by the facefly. The larvae develop in the fly for about 30 days and then move to the mouth of the fly. When the fly feeds near the eye, the larvae move out of the fly's mouth and migrate to the eye of the new host. In 3-6 weeks the larvae develop into adults and repeat the cycle. Transmission of the worm is by the face fly, Fannia canicularis. These flies ingest T. Californiensis eggs present in the ocular secretions when they feed on an infected host. The eggs develop into larvae within the fly's body cavity, which then are deposited onto the conjunctiva of the new host. The larvae mature and the adult worms deposit their ova in the lacrimal ducts of the host. Controlling the fly population would be helpful to reduce spread of this particular nematode.

Generally animals show few signs of the infestation. They may produce more tears, may be sensitive to light and occasionally develop conjunctivitis due to the irritation to the eye. The symptoms can become more serious if a secondary bacterial infection develops. In humans, T. Californiensis worms tend to reside in the superior and inferior fornices of the eye. The most common clinical findings in infected patients include a mild conjunctival inflammation, foreign body sensation, follicular hypertrophy of the conjunctiva and possibly excessive lacrimation. The worms may occasionally migrate across the ocular surface, eventually causing corneal scarring, opacity and blindness. Most of ocular T. Californiensis infestations in humans have occurred in California, particularly in the Sierra Nevada Mountains. In addition, this worm's habitat is also within the areas of New Mexico, Nevada and Oregon. The treatment of human T. Californiensis conjunctival infestation is simple. The symptoms usually resolve immediately after removal of the worms. Therefore, T. Californiensis infestation should be included in the differential diagnosis of patients with chronic conjunctivitis following hiking or camping in the mountains or back-country.


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