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

Abstract

Background For a long time known as the oriental eyeworm, Thelazia callipaeda is a zoonotic nematode that infects the eyes of a wide range of vertebrate hosts including dogs, cats, wildlife carnivores, lagomorphs, and humans. The high occurrence of this infection in Europe and the first cases in the United States have increased scientific interest in the parasite, as it also represents a risk for people living in endemic areas. Therefore, treatment and prevention of thelaziosis in canine population are advocated to reduce the risk of human infection as well. Here, we assessed the efficacy of a formulation containing sarolaner/moxidectin/pyrantel (Simparica Trio®) administered orally at monthly intervals, for the prevention of establishment of infection with T. callipaeda in naturally infected dogs. In this formulation, moxidectin is expected to have efficacy against eyeworms, whereas sarolaner and pyrantel are not. Methods The study was conducted in eyeworm endemic areas of Italy and France, where dogs (n = 125) were assigned into two groups consisting of a negative control group (G1; n = 62), in which animals were treated monthly with a control product (sarolaner; Simparica®), and a treatment group (G2; n = 63) in which animals were treated monthly with Simparica Trio (sarolaner/moxidectin/pyrantel) from day 0 to day 150. In total, nine animals were withdrawn from the study (two animals became positive at day 30, and seven for reasons unrelated to eyeworm infection), resulting in 116 animals (n = 58 for G1; n = 58 for G2). Results In G1, 16 out of 58 animals (27.6%) were observed with eyeworms during the study, and none of the animals from G2 were ever observed with eyeworms, resulting in 100% efficacy (P < 0.0001) in the prevention of establishment of T. callipaeda infection. Adult nematodes and fourth-instar (L4)-stage larvae were recovered from the eyes of positive animals, counted, and morphologically identified as T. callipaeda. In addition, specimens from Italy were molecularly confirmed as belonging to the haplotype 1 (i.e., the only one circulating in Europe so far). Conclusions Data presented herein demonstrated 100% efficacy of Simparica Trio for the prevention of T. callipaeda eyeworm infection in dogs from highly endemic areas of France and Italy. The use of this formulation is advantageous, as it is a licensed product in Europe with a wide efficacy spectrum against other nematodes, multiple tick species, and fleas. In addition, preventing the development of infection in dogs could also be a prophylaxis measure for zoonotic T. callipaeda infection in humans inhabiting endemic areas. Graphical Abstract

Emergence of Thelaziosis Caused byThelazia callipaedain Dogs and Cats, United States

“…Adopting proper diagnosis and surveillance measures is critical to limit the spread of this zoonotic parasite. Studies on control and treatment approaches for dogs suggest mechanical removal of adult and larval T. callipaeda nematodes coupled with the administration of diverse deworming drugs is effective ( 12 ). Because vector control using fly repellents is ineffective ( 3 ), control of T. callipaeda infections mainly rely on diagnosis and timely anthelmintic treatment.…”

Prevention of Thelazia callipaeda Reinfection among Humans

“…To date, human thelaziosis has been described in 12 patients from Europe, including a casepatient in Serbia (7) reinfected by T. callipaeda eyeworms 5 years after an initial case, as in the case we describe here. A related study called for implementing preventive measures, such as vector control and treatment of domestic reservoirs (e.g., dogs), to avoid zoonotic human infection (8). In addition, wild carnivore reservoirs, such as red foxes and wolves, should be considered as sources of infection for humans who frequent the same forest areas (9).…”

Occurrence of Thelazia callipaeda and its vector Phortica variegata in Austria and South Tyrol, Italy, and a global comparison by phylogenetic network analysis

“…Thelazia callipaeda is usually found under the eyelid and the nictitating membrane, and is easily distinguishable from other nematodes that can affect the eye, such as Onchocerca lupi , which is embedded in the tissue around the eye and often associated with nodule formation [ 13 ]. In combination with the removal of the nematodes from the eye, macrocyclic lactones, such as moxidectin and milbemycin oxime, are useful for both the prevention of infection and its treatment [ 14 – 17 ].…”