RESUMEN
BACKGROUND: Dirofilaria immitis is a worldwide parasite that is endemic in many parts of the United States. There are many commercial assays available for the detection of D. immitis antigen, one of which was modified and has reentered the market. Our objective was to compare the recently reintroduced Witness® Heartworm (HW) Antigen test Kit (Zoetis, Florham Park, NJ) and the SNAP® Heartworm RT (IDEXX Laboratories, Inc., Westbrook, ME) to the well-based ELISA DiroChek® Heartworm Antigen Test Kit (Zoetis, Florham Park, NJ). METHODS: Canine plasma samples were either received at the Auburn Diagnostic Parasitology Laboratory from veterinarians submitting samples for additional heartworm testing (n = 100) from 2008 to 2016 or purchased from purpose-bred beagles (n = 50, presumed negative) in 2016. Samples were categorized as "positive," "borderline" or "negative" using our established spectrophotometric cutoff value with the DiroChek® assay when a sample was initially received and processed. Three commercially available heartworm antigen tests (DiroChek®, Witness® HW, and SNAP® RT) were utilized for simultaneous testing of the 150 samples in random order as per their package insert with the addition of spectrophotometric optical density (OD) readings of the DiroChek® assay. Any samples yielding discordant test results between assays were further evaluated by heat treatment of plasma and retesting. Chi-square tests for the equality of proportions were utilized for statistical analyses. RESULTS: Concordant results occurred in 140/150 (93.3%) samples. Discrepant results occurred in 10/150 samples tested (6.6%): 9/10 occurring in the borderline heartworm (HW) category and 1/10 occurring in the negative HW category. The sensitivity and specificity of each test compared to the DiroChek® read by spectrophotometer was similar to what has been reported previously (Witness®: sensitivity 97.0% [94.1-99.4%], specificity 96.4% [95.5-100.0%]; SNAP® RT: sensitivity 90.9% [78.0-100.0%], specificity 98.8% [96.0-100.0%]). There were significant differences detected when comparing the sensitivities of the SNAP® RT and the Witness® HW to the DiroChek® among the 150 total samples (p = 0.003) and the 50 "borderline" samples (p = 0.001). CONCLUSIONS: In this study, the sensitivity of the Witness® HW was higher than the sensitivity of the SNAP® RT when compared with the DiroChek® test results prior to heat treatment of samples.
Asunto(s)
Antígenos Helmínticos/sangre , Dirofilaria immitis/aislamiento & purificación , Dirofilariasis/diagnóstico , Enfermedades de los Perros/diagnóstico , Ensayo de Inmunoadsorción Enzimática/métodos , Animales , Dirofilaria immitis/inmunología , Dirofilariasis/sangre , Dirofilariasis/parasitología , Enfermedades de los Perros/sangre , Enfermedades de los Perros/parasitología , Perros , Sistemas de Atención de Punto , Sensibilidad y EspecificidadRESUMEN
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.