BackgroundThe relative efficacy of a collar containing 10% imidacloprid and 4.5% flumethrin (Seresto®, Bayer HealthCare Animal Health) and a spot on formulation containing 10% imidacloprid and 2.5% moxidectin (Advocate®, Bayer HealthCare Animal Health) was evaluated as a control measure to prevent canine thelaziosis in dogs in an endemic area of France.FindingsNinety-six privately-owned dogs were enrolled in the multicentre, controlled study. Before summer (the period of transmission by fruit flies), dogs were allocated to one of three groups: Group A (n = 36)- treated once with a collar containing 10% imidacloprid and 4.5% flumethrin; Group B (n = 33)- treated every month for 8 months with a spot-on containing imidacloprid 10% and moxidectin 2.5%; and Group C (n = 27)- untreated control animals. Dogs were regularly subjected to ocular examination in order to assess Thelazia callipaeda infection. During the trial, T. callipaeda nematodes were detected in 12 (33%) collared dogs (group A) whereas no eyeworm could be found in dogs who received a monthly spot on application of moxidectin (group B). In the control group, 8 (30%) dogs became infected.ConclusionsThe monthly application of a spot on formulation containing 10% imidacloprid and 2.5% moxidectin was shown to be highly effective in preventing T. callipaeda infection in a population of dogs living in an endemic area in France. On the contrary, the slow-release collar tested in this study did not display any protection against canine thelaziosis.