Microfilarial reduction following ProHeart® 6 and ProHeart® SR-12 treatment in dogs experimentally inoculated with a resistant isolate of Dirofilaria immitis.

BACKGROUND: Emerging resistance of heartworms (Dirofilaria immitis) to macrocyclic lactone (ML) preventives is an increasing concern for veterinarians, pet owners and animal health companies that supply heartworm preventives, with recent reports of resistant isolates identified from the Mississippi Delta region of the United States. Products that are effective in eliminating microfilariae (MF) in dogs harboring resistant heartworm infections could be important in reducing the spread of heartworm resistance. The current study was conducted to investigate the potential for ProHeart® 6 (PH 6; Zoetis) and ProHeart® SR-12 (PH 12; Zoetis) to reduce MF in dogs experimentally inoculated with an isolate of D. immitis (ZoeMo-2012) confirmed to be resistant to MLs. METHODS: Twenty-three dogs with preexisting heartworm infections (via surgical transplantation) were randomly allocated to four groups based on pretreatment (Day -14) MF counts. On Day 0, dogs received a subcutaneous injection of either saline (placebo-treated control, 6 dogs), PH 6 (0.17 mg/kg, 6 dogs), PH 12 (0.5 mg/kg, 5 dogs) or a single oral dose of moxidectin powder in a gelatin capsule (0.25 mg/kg, 6 dogs). All dogs were bled for MF counts (modified Knott's test) on Days 0 (pretreatment), 1, 3, 7, 14, 21, 28, 42, 56, and 84. Dogs in control and PH 6 groups were also bled for MF counts on Days 112, 140, and 168. No adverse events associated with treatment were observed for any dog. RESULTS: Average reductions in MF counts compared with controls for PH 6 were 9.7% on Day 1, increasing to 75.0% on Day 7, and further to 86.5% on Day 28. On Day 42, average MF reduction increased to 90.3%. Reductions increased further over the next several months with reductions of 91.3, 96.8, 96.6, and 98.9% on Days 56, 84, 112, and 140, respectively. On Day 168, the reduction was 99.3% (P < 0.0001). Average reductions in MF counts compared with controls for PH 12 were 20.9% on Day 1, increasing to 78.9% on Day 7, and further to 91.2% on Day 28. On Day 84, the reduction was 96.9%. For dogs receiving a single oral moxidectin (0.25 mg/kg) on Day 0, reductions in MF were 86.3% on Day 1 and fluctuated between 74.4 and 83.6% through Day 28. On Days 42 and 56, percentage reductions were 87.1 and 81.8%, respectively, and 92.6% at the final time point (Day 84). CONCLUSION: Both PH 6 and PH 12 were highly effective in reducing the MF levels of a confirmed ML-resistant heartworm isolate following a single dose.

Evaluation of the efficacy of ProHeart® 6 (moxidectin) against a resistant isolate of Dirofilaria immitis (JYD-34) in dogs.

BACKGROUND: In a previous study, it was demonstrated that ProHeart® 6 (PH6) (moxidectin, Zoetis) provided only about 20% efficacy in a small six-dog study against a macrocyclic lactone -resistant Dirofilaria immitis isolate (Jd2009-2) when dogs were inoculated with infective third-stage larvae (L3) at the end of the dosing period (ie, 180 days post treatment). The objective of the current study was to determine the prophylactic efficacy of a moxidectin sustained-release formulation (PH6) against a confirmed macrocyclic lactone-resistant isolate of D. immitis (JYD-34) in dogs when administered by subcutaneous injection at the labeled dose of 0.17 mg/kg 2 days before L3 inoculation. This was intended to model the scenario where dogs become infected with resistant heartworms at the end of the PH6 treatment period (ie, 6 months post treatment) when dogs would routinely be given another injection under normal field use. METHODS: Twelve purpose-bred Beagle dogs (six males and six females) were selected and randomly allocated to two groups, untreated controls and PH6-treated dogs in groups of six each. The dogs were ≥8 months old at the start of the study, and using blood samples collected on Day -7 were shown to be negative for adult heartworm antigen and microfilariae. On Day 0, the dogs in the untreated control group were administered saline subcutaneously by injection, and the dogs in the treated group were administered PH6 according to label instructions. On Day 2, each dog was inoculated in the inguinal area with 50 L3 of D. immitis. The dogs were necropsied on Day 150 (148 days post infection), and the worms were collected and counted. RESULTS: All of the six control dogs were infected and harbored a range of 21 to 37 worms (geometric mean, 25.4; 10.9 males and 13.9 females). Only one of the six PH6 dogs was found to be infected, harboring a single male worm. Efficacy was 99.5% (geometric mean). CONCLUSION: ProHeart® 6 was highly effective in preventing the development of heartworms in dogs challenged with a confirmed macrocyclic lactone-resistant heartworm isolate (JYD-34) 2 days prior to treatment.

Evaluation of sarolaner and spinosad oral treatments to eliminate fleas, reduce dermatologic lesions and minimize pruritus in naturally infested dogs in west Central Florida, USA.

BACKGROUND: An in-home investigation of naturally flea infested dogs was conducted in West Central Florida, USA to evaluate and compare the effectiveness of two different oral flea adulticides to control flea infestations, minimize dermatologic lesions and reduce pruritus over an 8-week period. METHODS: Twenty-nine dogs living in 19 homes and another 26 dogs residing in 16 different homes were orally administered either a sarolaner or spinosad chewable, respectively on day 0 and once between days 28-30. Products were administered by study personnel according to label directions. Flea populations on dogs were estimated using visual area counts and flea infestations in the indoor premises were assessed using intermittent-light flea traps on days 0, 7, 14, 21 and once between days 28-30, 40-45, and 56-60. Assessments of dermatologic lesions were conducted monthly during the study and severity of pruritus was evaluated throughout the study on the same schedule as flea counts were conducted. Concurrent treatments for existing skin disease were not allowed. RESULTS: The administration of sarolaner or spinosad reduced flea populations on dogs by 99.0% and 97.3%, respectively within 7 days. Flea infestations on the sarolaner- and spinosad-treated dogs were reduced by > 99% at every counting period from day 14 post-treatment through the end of the 8-week study. At the end of the study 96.4 and 92.0% of the dogs treated with sarolaner and spinosad, respectively were flea-free. Flea populations in the indoor premises were also markedly reduced the end of the study, with 100 and 99.8% reductions in flea trap counts in the sarolaner and spinosad treatment groups, respectively. FAD lesion scores, atopic dermatitis lesions scores (CADESI-4) and pruritus severity scores were also markedly improved with both formulations. CONCLUSIONS: An in-home clinical field study conducted during the summer of 2016 in subtropical Florida demonstrated that two-monthly administrations of either sarolaner or spinosad chewables almost completely eliminated flea infestations on dogs and in private residences, while markedly reducing dermatology lesions and pruritus.