title: Efficacy of four commercially available heartworm preventive products against the JYD-34 laboratory strain of Dirofilaria immitis.
abstract: BACKGROUND
  Heartworm disease in dogs can be severe and life threatening. Resistance to available heartworm preventives was considered among potential causes of increased reports of failed heartworm prevention in dogs. The objective of the present study was to compare the efficacy of four commercially available heartworm disease preventives against the JYD-34 strain of D. immitis.
  
  
  METHODS
  Forty laboratory-reared dogs approximately 6 months old were used. Each dog was infected with fifty, third-stage heartworm larvae on study day (SD) -30. On SD-1, the dogs were randomized to five groups of eight dogs each. On SD-0, dogs in groups 1-4 were treated as follows: Group 1: ivermectin/pyrantel pamoate chewable tablets; Group 2: milbemycin oxime/spinosad tablets; Group 3: selamectin topical solution; and Group 4: imidacloprid/moxidectin topical solution. Dogs in Group 5 were not treated and served as controls. The dogs were treated according to their current body weights and labelled dose banding for each product. Groups 1, 2, and 3 were retreated with their respective products and current body weights on SD 31 and 60. On SDs 124-126 the dogs were euthanized and necropsied for recovery of adult heartworms.
  
  
  RESULTS
  Adult heartworms were recovered at necropsy from each of the dogs in the control group (13-32 worms/dog, geometric mean (GM) = 18.4 worms/dog). Adult heartworms and/or worm fragments were also recovered from each of the dogs treated with ivermectin/pyrantel pamoate, milbemycin oxime/spinosad or selamectin. Geometric means of worms recovered from dogs in each of these groups were 13.1, 8.8, and 13.1, resulting in efficacies compared to controls of 29.0, 52.2, and 28.8 %, respectively. All dogs in Group 4 (imidacloprid/moxidectin) were free of adult heartworms (100 % efficacy).
  
  
  CONCLUSIONS
  The combination of imidacloprid/moxidectin was 100 % effective in this study in preventing development of JYD-34 laboratory strain of D. immitis in dogs following a single treatment, while three monthlytreatments of the three other commercial products provided less than 100 % efficacy. The high efficacy achieved with imidacloprid/moxidectin was likely due to the unique pharmacokinetic properties of the topical formulation delivering greater and sustained drug concentrations necessary to prevent development of D. immitis larvae.
authors.affiliation: Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL, USA. blagbbl@auburn.edu.
authors.forename: Byron L
authors.initials: BL
authors.lastname: Blagburn
authors.affiliation: Clinical Development, Bayer HealthCare, Animal Health Division, Shawnee, KS, USA.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Arther
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, AL, USA.
authors.forename: Allen R
authors.initials: AR
authors.lastname: Dillon
authors.affiliation: Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL, USA.
authors.forename: Jamie M
authors.initials: JM
authors.lastname: Butler
authors.affiliation: Department of Pathobiology, College of Veterinary Medicine, Auburn University, Auburn, AL, USA.
authors.forename: Joy V
authors.initials: JV
authors.lastname: Bowles
authors.affiliation: Clinical Development, Bayer HealthCare, Animal Health Division, Shawnee, KS, USA.
authors.forename: Cristiano
authors.initials: C
authors.lastname: von Simson
authors.affiliation: Clinical Development, Bayer HealthCare, Animal Health Division, Shawnee, KS, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Zolynas
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000008:administration & dosage*; D004183:Dirofilaria immitis / Q000187:drug effects*; D004184:Dirofilariasis / Q000188:drug therapy*; D004283:Dog Diseases / Q000188:drug therapy*; D004285:Dogs; D016896:Treatment Outcome
chemical_list: D000871:Anthelmintics
keywords: Canine; Dirofilaria immitis; Efficacy; Heartworm; JYD-34; Macrocyclic lactone; Prevention; Resistance