Summary
Forty 11- to 12-week-old helminth-naive Beagles were categorized by sex and weight and randomly assigned to 4 treatment groups (group 1, ivermectin/ pyrantel pamoate; group 2, milbemycin oxime; group 3, untreated control; group 4, diethylcarbamazine/ oxibendazole). Each pup was inoculated po with approximately 100 infective Ancylostoma caninum larvae 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, and subsequent treatments were administered according to label recommendations at 30-day intervals (groups 1 and 2) or 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 intervals, and clinical observations of health status were conducted twice daily. Pups were euthanatized on day 90, and total gastrointestinal worm burdens were determined.
Compared with the mean A caninum egg counts of group-3 control pups, egg counts in group-1 pups were significantly (P ≤ 0.0001) lower on every sampling date from day 28 to 90, egg counts of group-2 pups were significantly (P ≤ 0.0001) lower on sampling days 35, 42, 49, 63, 70, 77, and 84, and were consistently the highest of all treated groups, and egg counts of group-4 pups were significantly (P ≤ 0.0001) lower on every sampling date from day 14 to day 90, and were consistently the lowest of all treated groups. Compared with mean A caninum 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 hookworms recovered at necropsy were significantly (P ≤ 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 were 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 infected pups receiving ivermectin/pyrantel, milbemycin oxime, or diethylcarbamazine/oxibendazole at label dosages, but the observed performance of all products was consistent with their respective label indications.
