Eyeworm Emergence in Cats & Dogs in the United States

In the Literature

Manoj RRS, White H, Young R, et al. Emergence of thelaziosis caused by Thelazia callipaeda in dogs and cats, United States. Emerg Infect Dis. 2024;30(3):591-594. doi:10.3201/eid3003.230700

The Research …

Thelazia spp (ie, eyeworms) are nematodes transmitted by muscoid and drosophilid flies and found in the conjunctival or lachrymal sacs of hosts.¹ Several species have been identified in the United States, including Thelazia gulosa in cattle, Thelazia lacrymalis in horses, and Thelazia californiensis in dogs and wildlife; infections in humans have also been reported.^1-3

In this study, 2 cases of Thelazia callipaeda infection were reported in cats in New York with no known travel history. The first cat was presented with crusty lesions and swelling of the right eye that progressed to squinting and mucus accumulation; 4 worms were manually removed via saline flush. The second cat had no clinical signs, and worms were found during routine physical examination; 8 worms were manually removed following administration of local anesthesia. T callipaeda were primarily identified by morphologic characteristics; genetic sequencing was performed on one worm. Both cats were treated with different topical anthelmintics and recovered completely.

T callipaeda infection can result in clinical signs ranging from inflammation and lacrimation to photophobia, severe conjunctivitis, and blindness and has historically been identified in dogs, cats, and rabbits in Asia and Europe.^4,5 The feline infections reported in this study, however, as well as previously reported canine infections suggest emergence in the United States.

Thelazia spp infections in humans primarily originate from rabbits⁶; however, red foxes also transmit and distribute these parasites, especially in Europe.⁵ Geographic spread of Thelazia spp is facilitated by use of various hosts for transmission and reproduction, as well as increased travel of humans and pets.

… The Takeaways

Key pearls to put into practice:

• Thelazia spp infections can be unilateral or bilateral and may not result in apparent clinical signs. Thorough examination of both eyes is therefore important for diagnosis, especially in areas where eyeworms are endemic or emerging.

• No anthelmintics are labeled for Thelazia spp infection, but several can help eliminate infection. Surgical or mechanical removal of visible worms is important to help alleviate patient discomfort and prevent infection of additional hosts.

• Controlling intermediate fly hosts is impractical. In areas where Thelazia spp are endemic or infections have been reported, pet owners should be educated on how eyeworms are transmitted to help prevent infection, especially when one or more pets in a household have had a previous infection.