Autochthonous Thelazia callipaeda Infection in Dog, New York, USA, 2020

We report a case of autochthonous infection of the eye worm Thelazia callipaeda in a dog in the northeastern United States. Integrated morphologic identification and molecular diagnosis confirmed the species. Phylogenetic analysis suggested introduction from Europe. The zoonotic potential of this parasite warrants broader surveillance and increased awareness among physicians and veterinarians.

metamorphosis, infective third-stage larvae (L3) are passed via the labelum onto the conjunctiva of another suitable host. L3 develop into adults that migrate to the conjunctival recess, lacrimal ducts, or both, resulting in conjunctivitis, ocular discharge, and blepharospasm. Female worms release more L1, seeding ocular secretions of the host, and conclude the life cycle (1,2). Intermediate hosts for Thelazia nematodes are dipteran fl ies of the genera Phortica for T. callipaeda, Fannia for T. californiensis, and Musca for T. gulosa (1,5,7,8). P. variegata fruit fl ies are widely distributed across Eurasia and have been found in multiple areas in the eastern United States (9). In North America, they have been experimentally proven to be competent vectors for T. callipaeda worms (10), supporting the potential occurrence of T. callipaeda infection in the United States (2). We report T. callipaeda eye worm infection detected in a dog in the Western Hemisphere in November 2020.

The Case
The patient was a 7. We report a case of autochthonous infection of the eye worm Thelazia callipaeda in a dog in the northeastern United States. Integrated morphologic identifi cation and molecular diagnosis confi rmed the species. Phylogenetic analysis suggested introduction from Europe. The zoonotic potential of this parasite warrants broader surveillance and increased awareness among physicians and veterinarians.
mL ivermectin in physiological saline solution, led to recovery of 12 nematodes. After systemic ivermectin administration, no recurrence has been noted. Four nematodes (3 female, 1 male) were morphologically identified as T. callipaeda eye worms on the basis of the cuticular transverse striations (CTS) pattern and vulva position (1,6). The 3 female worms were 12.7-13.9 mm long and 314-360 µm wide. The vulval opening was anterior to the esophageal intestinal junction, and in 1 specimen it was 610.86 µm from the cephalic end. The midbodies contained 150-190 CTS/mm, and the cephalic/caudal region contained 220-240 CTS/mm. The buccal capsule was wider than it was deep. Two protruding phasmids were visible at the tip of the tail, which did not taper unilaterally ( Figure 1). The male worm was 8.9 mm long, and its width was not measured. The cephalic region contained 310 CTS/mm, and the midbody/caudal region contained 170 CTS/mm. The small spicules measured 147.73 µm; the large spicules, 1721.90 µm.
We subjected a female worm to DNA extraction and multilocus PCR (18S rRNA, 12S rRNA, and cytochrome oxidase c subunit 1 [cox1] gene markers) by using assays described previously (4,11), followed by sequencing. The partial sequences generated for 18S rRNA matched 99.7%, 12S rRNA 99.4%, and cox1 genes 93.3%-100% of the corresponding genes of T. callipaeda worms in GenBank. We deposited the generated sequences in GenBank (accession no. MW570771 for 18S rRNA, MW575766 for 12S rRNA, and MW570733 for cox1). Molecular data unequivocally confirmed the parasite as T. callipaeda. Phylogenetic analysis of the cox1 gene showed that the T. callipaeda eye worm found in North America belongs to the haplotype-1 prevalent in Europe (100% maximum identity), suggesting a possible source of introduction ( Figure 2).

Conclusions
The discovery of an autochthonous case of T. callipaeda eye worm infection in the United States suggests its introduction and establishment on a continent where natural infection has not been documented. The report on the distribution of P. variegata fruit flies in the eastern United States and their competence for T. callipaeda eye worms has raised concern for eye worm infections in animals and humans in this region (10). Our finding is in line with previous predictions. Active surveillance of all susceptible hosts, coupled with ecologic niche modeling as conducted in Europe, can help gauge the extent of T. callipaeda eye worm spread in North America (7). Our findings should bring awareness about this invasive, zoonotic parasite to veterinary and medical ophthalmologists in the Americas. To curtail the potential spread in the United States, consideration should be given to US Department of Agriculture-imposed requirements for implementing broad and accurate parasite diagnostic methods and prophylactic anthelmintic treatment to mitigate the introduction of exotic parasites before relevant species are imported. The One Health model of cooperation among veterinarians, wildlife biologists, and physicians is vital for assessing the current distribution and mitigating the spread of this multihost parasite with zoonotic potential. As this case shows, emergence of T. callipaeda parasites requires increased awareness by both human medical and veterinary professionals.