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DPDx

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Thelaziasis

[Thelazia spp.]

 Mid-section of a gravid female Thelazia sp., showing many typical	 spirurid-type eggs.

Mid-section of a gravid female Thelazia sp., showing many typical spirurid-type eggs.


Anterior end of a female Thelazia sp. Note the lack of lips (arrow) and prominent striations.

Anterior end of a female Thelazia sp. Note the lack of lips (arrow) and prominent striations.

Causal Agents

Spirurid nematodes in the genus, Thelazia. Two species that have been implicated in human infection include T. callipaeda (the Oriental eye worm) and T. californiensis (the California eye worm).


Life Cycle

Life cycle of Thelaziasis

Dogs and other canids, cattle, and horses are the usual definitive hosts for Thelazia spp., although other mammals, including cats, lagomorphs, cervids and humans, can also become infected. Adults reside in the conjunctival sac of the definitive host The number 5 where they shed first-stage larvae The number 1. These larvae are sheathed. The first-stage larvae are ingested by the intermediate host (usually flies, including drosophilid flies in the genus, Amioto, and muscid flies in the genera, Musca and Fannia), when they feed on tears and other lacrimal secretions The number 2. In the digestive tract of the intermediate host, the larvae shed the sheath and invade various host tissues, including the hemocoel, fat body, testis and egg follicles where they develop in capsules. The encapsulated larvae become infective L3 larvae The number 3 after two molts. Afterwards, the L3 larvae break out of the capsules and migrate to the fly’s mouthparts, where they remain until the fly feeds on the tears of the definitive host. The larvae invade the conjunctival sac of the definitive host and become adults after about a month and two additional molts The number 4. Humans may also serve as a final host The number 6, after infected flies feed on tears or other lacrimal secretions.

Geographic Distribution

Presumed worldwide; human infections have been recorded from the United States, China, Russia, India, Japan, and Thailand.

Clinical Presentation

Adults in the eye cause varying degrees of inflammation and lacrimation. In heavier infections, photophobia, edema, conjunctivitis, and blindness may occur.

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  • Page last reviewed November 29, 2013
  • Page last updated November 29, 2013
  • Content source: Global Health - Division of Parasitic Diseases and Malaria
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