COMPARISON OF THE EFFICACIES OF 3 HEARTWORM PREVENTIVES AGAINST EXPERIMENTALLY-INDUCED INFECTIONS WITH ANCYLOSTOMA-CANINUM AND TOXOCARA-CANIS IN PUPS

Forty 11- to 12-week-old helminth-naive Beagles were categorized by se x and weight and randomly assigned to 4 treatment groups (group 1, ive rmectin/pyrantel pamoate; group 2, milbemycin. oxime; group 3, untreat ed control; group, 4, diethylcarbamazine/oxibendazole). Each pup was i noculated po with approximately 100 infective Ancylostoma caninum larv ae and 100 larvated Toxocara canis eggs on day 0, and repeatedly at 7- day intervals thereafter until day 56. Administration of anthelmintics also began on day 0, find subsequent treatments were administered acc ording to label recommendations at 30-day intervals (groups 1 and 2) o r daily (group 4) for a period of 90 consecutive days. Body weight and A caninum and T canis fecal egg counts were measured at weekly interv als, and clinical observations of health status were conducted twice d aily. Pups were euthanatized on day 90, and total gastrointestinal wor m burdens were determined. Compared with the mean A caninum eeg counts of group-3 control pups, egg counts in group-1 pups were significantl y (P less than or equal to 0.0001) lower on every sampling dare from d ay 28 to 90, egg counts of group-2 pups were significantly (P less tha n or equal to 0.0001) lower on sampling days 35, 42, 49, 63, 70, 77, a nd 84, and were consistently the highest of all treated groups, and eg g counts of group-4 pups were significantly (P less than or equal to 0 .0001) lower on every sampling dare from day 14 to day 90, and were co nsistently the lowest of all treated groups. Compared with mean A cani num egg counts of group-3 pups, egg counts in group-1 and group-2 pups were lower by 97.8 and 90.8%, respectively. Numbers of adult hookworm s recovered at necropsy were significantly (P less than or equal to 0. 05) lower by 99.4, 83.9, and 99.9% in groups 1, 2, and 4, respectively . Patent T canis infections were detected in 11 of 40 pups and only 5 adult worms were recovered from 4 pups at necropsy. These findings wer e attributed to age resistance to T canis by maturing pups rather than to a primary pharmacologic effect. This study identified substantial differences in the quantities of hookworm eggs in experimentally infec ted pulls receiving ivermectin/pyrantel, milbemycin oxime, or diethylc arbamazine/oxibendazole at label dosages, but the observed performance of all products was consistent with their respective label indication s.