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

Abstract

T helaziasis in dogs can be caused by 2 nematodes of the genus Thelazia (Nematoda: Spirurida): T. callipaeda and T. californiensis (1). The oriental eye worm (T. callipaeda) is a helminth that infects a variety of domestic and wild carnivores, lagomorphs, rodents, and primates (including humans) across Eurasia (2,3). In Europe, the T. callipaeda eye worm is an emergent vectorborne helminth that has spread steadily across all countries over the past 3 decades (2). The California eye worm (T. californiensis) has been reportedly found in wild and domestic carnivores, ungulates, lagomorphs, and humans; its range is limited to the western United States (4). Zoonotic infection of humans with a third species of eye worm (T. gulosa), which infects cattle, has recently been reported in the western United States (5). These 3 species of Thelazia eye worm with zoonotic potential are morphologically and biologically distinct (1,5,6).Thelazia nematodes are found in the conjunctival recesses of the eye (1). Secretophagous dipteran intermediate hosts (1,7) ingest fi rst-stage larvae (L1) while feeding from the defi nitive host's eyes. After 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.

Emergence of Thelaziosis Caused by Thelazia callipaeda in Dogs and Cats, United States

“…Phylogenetic analysis of the cox1 sequences revealed clustering as a monophyletic clade with T. callipaeda haplotype 1 from Europe ( 10 , 11 ) ( Appendix Figure 2 ). This study and the previous report on a dog ( 1 ) reconfirm the possibility that this parasite was introduced from Europe and subsequently spread in the United States.…”

“…Therefore, prophylactic anthelmintic administration coinciding with fly seasons would be an effective control strategy. Furthermore, as indicated in previous reports (1,4), adoption of a holistic One Health approach will be effective in further limiting the spread of T. callipaeda eyeworm in North America.…”

“…Thelazia callipaeda eyeworm was considered an exotic parasite in North America until an autochthonous case was reported in a dog from New York, USA, in 2020 ( 1 ). T. callipaeda eyeworm has been reported in countries in East Asia and the Soviet Union, later expanding its geographic range into Europe ( 2 , 3 ).…”

Efficacy of a formulation of sarolaner/moxidectin/pyrantel (Simparica Trio®) for the prevention of Thelazia callipaeda canine eyeworm infection

“…For example, Simparica Trio is currently licensed in Europe for nematodes, ticks, and fleas [ 26 ]. In addition, the same product is licensed for the treatment of parasitic nematode and ectoparasite infestation in dogs in the USA, where the first autochthonous case of T. callipaeda in a dog was published in 2021 [ 36 ]. This advantage makes the product a good candidate and increases the options for products highly efficacious in treating and preventing infection by this eyeworm in dogs.…”