The commercial formulation of milbemycin oxime (Milbemax®) at the minimal dose of 0.5 mg/kg and 2 mg/kg b.w. for dogs and cats, respectively, also containing praziquantel (5 mg/kg b.w.), showed a high therapeutic efficacy in curing T. callipaeda in naturally infested animals. In dogs the efficacy was 72.7% and 90.9% after a single or two treatments, at a weekly interval, both significantly differing from the placebo group. In cats, the therapeutic efficacy was 53.3% and 73.3% after a single or two treatments, at a weekly interval. It is known that praziquantel is not efficacious against nematodes. Since both actives of Milbemax®, milbemycin oxime and praziquantel, are well established on the market and known not to interfere with each other, it can be assumed that other formulations containing milbemycin oxime alone or in combination with other actives (e.g., Interceptor®, Sentinel®, Sentinel Spectrum® and Program Plus®; all Novartis Animal Health) may be efficacious against T. callipaeda. Furthermore, since T. callipaeda lives in the conjunctival pouches of the final host, an accurate dosing to ensure optimal blood concentrations of milbemycin oxime is needed to reach efficacious concentrations of the product in the conjunctives. This may explain the reasons for a higher efficacy of the product after a second treatment one week after the first, as also suggested by the results of a preliminary study on T. callipaeda naturally infested animals . A lower efficacy observed on the 13 dogs (excluded from the statistical analysis) in which the treatment was administered without food, highlights the importance of a correct administration of the drug.
This study first evaluated the therapeutic efficacy of milbemycin oxime and praziquantel against T. callipaeda in cats. In addition, on the basis of a previous study in which the monthly administration of milbemyin oxime in dogs was highly effective (96.7%) for the prophylaxis of T. callipaeda, it may be argued that a similar prophylactic effect might occur in cats. This hypothesis deserves to be further tested under field conditions. Treatment of thelaziosis is an important issue in animals living in endemic areas, such as Basilicata in Italy (prevalence up to 60%; ), or Spain (prevalence of 39.9%; ) and Switzerland (prevalence up to 5%; ). An efficacious treatment against T. callipaeda is useful for pet owners considering the spread of the parasite in areas previously regarded as non endemic, such as France  and Spain .
The reasons for such an increase in cases of thelaziosis in dogs and cats throughout Europe are unknown, but it could be related to the spread of vector populations as well as to the occurrence of the infestation in wildlife species (e.g., foxes, wolves, beech martens and brown hares), which act as reservoirs for T. callipaeda. Therefore, domestic animals which are traveling together with their owners from non-endemic to areas endemic for T. callipaeda should be treated since they are at risk of acquiring thelaziosis, as reported for some dogs in France or Germany [10, 22]. Thus, monthly anthelmintic treatments, which are already recommended as a control strategy for dirofilarioses and other helminth infestations (e.g. see ESCCAP.org), should be considered for animals living in areas endemic for T. callipaeda in order to eliminate larval stages soon after their transmission from the drosophilid flies, thus interrupting the host-parasite transmission chain [17, 23]. The high level of efficacy demonstrated in the current study suggests that further investigations should be carried out in order to test the effectiveness of the product when administered monthly during the risk season, in preventing T. callipaeda infestations in dogs and cats.
In addition, since Milbemax®-tablets for cats are flavor coated and chewable tablets are available for dogs, the oral formulations are very easy to apply, compared to the non-licensed local instillation of antiparasitic drugs [18, 19] or to the mechanical removal of parasites from eyes. This especially applies when dealing with non-cooperative dogs and cats, where restraining them for manipulations around the eyes or even for spot-on applications is particularly difficult and bears the risk of trauma. Furthermore, wet coats or rainy days are reported to reduce the efficacy of topical administrations , a problem that is avoided by the drug administration per os.