Efficacy of a novel orally administered combination product containing sarolaner, moxidectin and pyrantel (Simparica Trio™) against induced infestations of five common tick species infesting dogs in the USA

Background The efficacy of a novel oral combination product, Simparica Trio™, containing sarolaner, moxidectin and pyrantel was evaluated against five tick species that commonly infest dogs in the USA, Amblyomma americanum, Amblyomma maculatum, Dermacentor variabilis, Ixodes scapularis and Rhipicephalus sanguineus. Methods Laboratory studies were conducted against two different strains of each tick species. In each study, 10 purpose-bred Beagle or mixed-breed dogs were randomly allocated to one of two treatment groups based on pre-treatment host-suitability tick counts. Dogs were infested with approximately 50 (45–55) unfed adult ticks on Days -2, 5, 12, 19, 26 and 33. On Day 0, dogs received either a single oral dose of Simparica Trio™ at the minimum label dose of 1.2 mg/kg sarolaner, 24 µg/kg moxidectin and 5 mg/kg pyrantel (as pamoate salt) or placebo. Tick counts were conducted at 48 h post-treatment and after each subsequent weekly re-infestation for A. maculatum, D. variabilis, I. scapularis and R. sanguineus studies and at 48 hours or at 72 h post-treatment and after weekly re-infestation in the first and second A. americanum studies, respectively. Results No treatment-related adverse reactions occurred in any study. In all studies, placebo-treated dogs maintained infestations throughout the entire study duration, and dogs treated with Simparica Trio™ had significantly lower (P ≤ 0.0010) mean live tick counts than placebo-treated dogs at all time-points. Against A. maculatum, D. variabilis, I. scapularis and R. sanguineus, a single oral dose of Simparica Trio™ evaluated at 48 h post-treatment provided ≥ 98.9% efficacy against existing infestations, and within 48 h of re-infestation efficacy was ≥ 90.4% through at least Day 28 (except for R. sanguineus on Day 14 in a single study with an efficacy of 89.7%). Against A. americanum, Simparica Trio™ provided ≥ 99.4% efficacy at ≤ 72 h after treatment of existing infestations and maintained ≥ 98.4% efficacy at ≤ 72 h after re-infestation through at least Day 35. Conclusions A single dose of Simparica Trio™ administered orally at the minimum label dosage of 1.2 mg/kg sarolaner, 24 µg/kg moxidectin and 5 mg/kg pyrantel provided treatment and control of the common tick species infesting dogs in the USA for at least one month.

Background Prevention and control of tick infestations remain major problems for dog owners within the USA and in many countries around the world [1][2][3]. Dogs infested with ticks can experience a broad range of clinical signs, ranging from local irritation and generalized hypersensitivity reactions to alopecia, tick paralysis and even anemia in extremely heavy infestations [3,4]. In addition to being parasites themselves, ticks are known to be a primary source of pathogen transmission to animals, and are second only to mosquitoes, with respect to the transmission of vector-borne pathogens to humans [2,[5][6][7][8]. The five hard tick species used in the studies reported here, i.e. Amblyomma americanum, Amblyomma maculatum, Dermacentor variabilis, Ixodes scapularis and Rhipicephalus sanguineus, represent all genera (and ~ 50% of the species) known to commonly infest dogs and cats in the USA [3,9,10]. Additionally, all five are known to act as vectors for important canine pathogens, including Anaplasma phagocytophilum and Borrelia burgdorferi transmitted by I. scapularis; Babesia canis, B. gibsoni and Ehrlichia canis transmitted by R. sanguineus; Ehrlichia ewingii transmitted by A. americanum; Hepatozoon americanum transmitted by A. maculatum; and Rickettsia rickettsii transmitted by D. variabilis [3,7,9,10]. The complexities of tick biology and ecology contribute to the difficulties associated with tick infestation prevention and control [4,7]. The majority of ticks important in canine health, including the five species studied here, are hard ticks with multiple life stages (larva, nymph and adult) that each feed on a unique host. The high reproductive capacity of ticks adds to the problem, with suitable environmental conditions promoting the presence of large numbers of immature and adult ticks questing for a canine host [3]. After finding a suitable passing host, ticks will attach to the animal and begin feeding. The time period between attachment to the host and the transmission of pathogens, which may be as long as 24-48 hours, is a window of opportunity in the control of tick infestation and the prevention of tick-borne pathogen transmission, providing the chance to interrupt the tick life-cycle and the spread of disease [3,11,12].
Sarolaner belongs to a potent new class of ectoparasiticides (isoxazolines) that provides broad activity against fleas and ticks [13]. Previously efficacy against ticks has been demonstrated by sarolaner alone [14]. Recently, a novel oral combination product containing sarolaner in addition to moxidectin and pyrantel (Simparica Trio ™ , Zoetis, Parsipanny, NJ, USA) has been developed. Not only will Simparica Trio ™ treat and control flea and tick infestations for one month in dogs [15], it will also treat roundworm and hookworm infections [16][17][18] and provide protection from lungworm [19] and heartworm disease [20].
The 10 studies reported here confirm the efficacy of Simparica Trio ™ against five common tick species infesting dogs in the USA, A. americanum, A. maculatum, D. variabilis, I. scapularis and R. sanguineus.

Methods
Ten laboratory studies were conducted to evaluate Simparica Trio ™ against the following common tick species of the USA: A. americanum (lone star tick; Studies 1 and 2); A. maculatum (Gulf Coast tick; Studies 3 and 4); D. variabilis (American dog tick; Studies 5 and 6); I. scapularis (black-legged tick; Studies 7 and 8); and R. sanguineus (brown dog tick; Studies 9 and 10). Ticks were obtained from multiple laboratory-maintained colonies (one study used wild-caught ticks) so that two different USA strains of each tick species were tested. All studies were conducted in accordance with the CVM Guidance for Industry #85, Good Clinical Practice [21] and the World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) guidelines for evaluating the efficacy of parasiticides for the treatment, prevention and control of flea and tick infestations on dogs and cats [22]. Masking was accomplished by separation of functions of study personnel. All personnel involved in making assessments of efficacy or safety were unaware of treatment assignments and dedicated personnel conducted the allocation of dogs and treatment dispensing, but did not conduct any other study observations.

Animals
Ten dogs were included in each treatment group. Dogs were purpose-bred Beagle or mixed breed, uniquely identified, ranging from 7 months to 12 years of age and weighed between 5.3 and 35.1 kg at study initiation. Dogs were deemed to be in good health by a veterinarian and had demonstrated good tick retention prior to treatment. The animals were housed individually in indoor pens such that no physical contact was possible throughout the study and were fed a commercial dog food ration sufficient for a maintenance diet. Fresh water was available ad libitum. Study participants used separate protective clothing and equipment between each animal to prevent any cross-contamination between dogs.

Design
Treatment day for all studies was designated as Day 0. The general health of each dog was assessed daily by a veterinarian for up to 3 weeks prior to treatment and for the duration of the study. Examinations included (but were not limited to) rectal temperature, thoracic auscultation, skin and hair assessment, and the overall physical health of the dog. Host suitability was determined prior to inclusion in the study and within 1 week of treatment on Day 0. All dogs were first examined to ensure they were free of ticks and then infested with 50 (± 5) viable, unfed ticks of the appropriate species. After 48 h (72 h for Study 2), live attached ticks were counted and removed, and the twenty dogs with the highest tick counts were selected for each study. Animals were allocated to treatments and pens according to a randomized complete block design, with room (if applicable) and block based on host suitability tick counts. Each dog was randomly allocated to a treatment group (Simparica Trio ™ or placebo) in each block, and all dogs within a block were randomized to adjacent pens. Dogs were weighed, moved to their allocated pens and infested with ticks on Day -2. On Day 0, all dogs were assessed for overall health and then orally administered either the placebo or Simparica Trio ™ . Tick infestations (50 ± 5 viable ticks) were repeated on Days 5, 12, 19, 26 and 33, and live tick counts were performed 48 h (72 h for Study 2) after treatment on Day 0 and again after each infestation.

Tick strains and infestations
Five tick species common in the USA were used in the ten studies, with two strains of USA origin used for each tick species. Outside of Study 8, which used wild-caught I. scapularis ticks collected within South Carolina during the two months prior to study start, ticks were obtained from laboratory-maintained colonies. These colonies were originally established using ticks collected from the field and had wild-caught ticks introduced into the tick colony within three years or less of the study start. For each infestation, 50 viable, unfed adult ticks with a sex distribution of approximately 1:1 were applied directly on each dog. Prior to infestation, three vials of ticks were randomly examined to demonstrate their correct preparation (number, sex ratio, viability, feed status). For Studies 2, 5, 8 and 10 the dogs were sedated prior to infestation; in all other studies dogs were not sedated.

Treatment
On Day 0, dogs were treated orally with either placebo tablets containing inert formulation ingredients (vehicle) or the combination product (Simparica Trio ™ ). Tablets were provided in varying strengths, such that a combination of tablets could be administered to ensure dogs were appropriately dosed to the minimum end of the label dose range. Each dog received one to three tablets of the combination product to provide as close as possible to the minimum label dosage of 1.2 mg/kg sarolaner (actual doses ranged from 1.2 to 1.6 mg/kg), 24 µg/kg moxidectin (actual doses ranged from 24.0 to 31.6 µg/kg) and 5 mg/ kg pyrantel (as pamoate salt) (actual doses ranged from 5.0 to 6.6 mg/kg) or the equivalent number of placebo tablets. Body weights obtained on Day -2 were used for dose calculation. Feed was withheld for at least 12 h prior to treatment and animals were not fed again until at least 4 h post-treatment. All doses were administered by hand pilling to ensure accurate dosing. Dogs were observed for several minutes following dosing to ensure the entire treatment was swallowed and for up to 2 h post-dosing for any signs of emesis. Dogs were examined for general health and any reactions to treatment at 1, 3, 6 and 24 h after treatment.

Tick counts
Tick counts were conducted by trained personnel either 48 h (9 studies) or 72 h (Study 2) after treatment on Day 0 or after each subsequent tick infestation. On each count day, the order in which the dogs were examined for tick counts was pre-defined by a randomization plan. Each dog was initially examined to identify readily visible ticks by pushing the dog's fur against its natural nap. Then, an extra-fine tooth comb was used to comb the animal thoroughly and identify any previously missed ticks. Dogs were examined for a minimum of 10 min, and if any tick was encountered in the final minute, the combing was extended in 1-min increments until no additional ticks were encountered. All identified ticks were removed and examined to assess viability. Personnel conducting counts were masked to treatment assignments and changed gloves and protective clothing between dogs.

Statistical analysis
The individual dog was the experimental unit and the primary endpoint was live tick count. Arithmetic means were used to summarize tick count by treatment group and time-point. The PROC MIXED procedure (SAS 9.4, Cary NC, USA) was used to analyse tick counts, using a mixed linear model with treatment group as a fixed effect and block, and error as random effects at each timepoint. If multiple rooms were used in the study then the random effects included room, block within room, and error. Testing was two-sided at the significance level α = 0.05. Percent efficacy was calculated from arithmetic means using Abbott's formula: In Study 5 (D. variabilis), one treated dog was removed from the study after being diagnosed with a strangulating inguinal hernia on Day 9. Consequently, least squares means (rather than arithmetic means) and corresponding efficacies were used for data collected on Days 14-35 for this study [23].

Amblyomma americanum
In studies using A. americanum, dogs in the placebotreated groups maintained tick infestations for the entire study duration, with live ticks collected from all dogs at all counts (Table 1)

Rhipicephalus sanguineus
In both Studies 9 and 10, live ticks were removed from control dogs infested with R. sanguineus with mean tick counts ranging from 11.7 to 34.7, representing 23.4-69.4% of the 50 ticks used for infestation (

Health observations
No post-treatment abnormal health observations were recorded from any dogs in Studies 1, 4, 7, 9 or 10. Abnormal health observations were recorded for a total of nine dogs from the remaining five studies, and none were deemed to be associated with treatment. Recorded events included mild reactions to tick infestation, including localized dermal response, target lesion due to tick bite and mild swelling (five dogs; four placebo-treated and one combination product-treated), otitis externa  and dermatitis (one placebo-treated), cherry eye (one combination product-treated) and mammary mass (one combination product-treated). As noted in the Methods section, a single placebo-treated dog was removed from Study 5 after being diagnosed with a strangulating inguinal hernia on Day 9.

Discussion
The ten studies reported here confirm the high and consistent efficacy of Simparica Trio ™ in treating existing infestations and controlling re-infestations of five common and important dog tick species in the USA. Trio ™ provides dogs with highly effective treatment of existing tick infestations and reliable protection from reinfestation between monthly treatments. Recently, ecological changes due to warmer temperatures and human modification in conjunction with the increased movement of hosts (human and animal) both within and across country borders have contributed to elevated tick densities in certain areas and the appearance of some species in new habitats [1,10,24,25]. Not surprisingly, the epidemiology of tick-borne diseases in animals also appears to be shifting, with some pathogens appearing to be re-emerging and others being reported in new geographic locales and host populations [1,2,5,7,10,26]. The rapid killing of ticks and the prevention of attachment and feeding are important in reducing infestation-associated clinical signs and preventing tick-borne disease transmission. Following host attachment, 24-48 hours is usually needed before ticks are able to transmit tick-borne pathogens to hosts [11,27]. After attaching, ticks first enter a slow feeding phase that lasts for 3-5 days before moving into a more rapid state of feeding [1]. The first few days after host attachment is a critical time in tick biology and provides a window of opportunity for intervention. Simparica Trio ™ administered to dogs has shown rapid efficacy against I. scapularis, beginning to kill ticks within 8 hours of administration against an existing infestation and providing ≥ 94.2% effectiveness against re-infestations within 24 hours for 28 days [28]. While the studies reported here did not focus on speed of kill, it is important to note that the efficacy of Simparica Trio ™ was ≥ 98.9% at the first post-treatment evaluations for all five tick species. Furthermore, of the 20 posttreatment evaluations conducted for each species over the course of 1 month (Day 28/29), at least 85% showed efficacy ≥ 99%, suggesting monthly administration of Simparica Trio ™ will effectively protect dogs from recurring tick infestations and may reduce the transmission of tick-borne diseases. While numerous parasite preventives are currently available for use in dogs, extensive protection against both ecto-and endoparasites usually requires multiple medications often with varying administration routes and directions [29]. Recent research in both the USA and Europe shows owner compliance in the prevention and treatment of internal and external parasites frequently falls short of expert recommendations [30][31][32][33][34]. Within the USA, 73% of dog owners in one survey believed their dog should receive year-round flea and tick preventives but only 13% actually purchased sufficient medication to achieve year-round protection [32], and owner compliance in the correct administration of canine heartworm preventive is documented as well below 100% [30,35]. The use of multiple medications may add further hurdles for owners; an analysis of clinic transaction records for 231,565 dogs receiving flea and tick medication showed approximately 66% of owners purchased insufficient protection to provide the veterinarian's recommended yearround protection [31]. If increased owner compliance, and consequently improved pet health, is to be achieved, then newly developed products need to provide comprehensive protection and thereby reduce the treatment burden on owners. Combining the proven preventive moxidectin [36][37][38][39] and anthelmintic pyrantel [40][41][42] with sarolaner, Simparica Trio ™ provides a means of aligning ectoparasite treatment and control with currently available endo-parasiticides, addressing the needs of pet owners by providing broad-spectrum parasite protection in a single convenient product.

Conclusions
A single oral dose of the combination product (Simparica Trio ™ ) administered at the minimum label dose of 1.2 mg/kg sarolaner, 24 µg/kg moxidectin and 5 mg/ kg pyrantel (as pamoate salt), displayed robust efficacy (≥ 98.9%) against existing infestations of five common USA tick species infesting dogs within 48 to 72 hours of administration. Efficacy at 48 hours against re-infestation by A. maculatum, D. variabilis, I. scapularis and R. sanguineus was ≥ 90.4% at Day 28. Efficacy at ≤ 72 hours against re-infestation by A. americanum, was ≥ 98.4% for at least 35 days. At all observations, Simparica Trio ™ significantly reduced live tick numbers of all species compared to controls. Simparica Trio ™ administered monthly provides owners and veterinarians with a highly effective means of treating and controlling tick infestations on dogs.