Previous work had indicated that the 2 canine hookworms, Ancylostoma caninum and Uncinaria stenocephala, may differ in their susceptibility to treatment with milbemycin oxime. Thus, the study reported here was to examine the effects of this drug on concomitant infections in experimentally infected dogs. Twenty specific-pathogen-free Beagles were inoculated orally with 500 infective-stage larvae from a mixture of larval A caninum and U stenocephala. Quantitative fecal examinations were performed weekly, beginning the day of infection. The dogs were assigned to 2 equal groups, 1 group that received the compound and 1 that received a placebo. The dogs were treated on postinoculation days 30, 60, and 90. For A caninum, egg counts dropped precipitously after the first treatment, and no eggs of this species were found in the feces of any of the treated dogs after the second treatment. The treatments had no significant effect on the mean egg counts made on U stenocephala, although 2 dogs stopped passing eggs entirely after the second treatment. At necropsy, no A caninum were found in any of the treated dogs; the mean number recovered from the control-group dogs was 56.1. Significant difference was not found in the mean number of adult U stenocephala recovered from the treated and control groups (27.0 and 21.7, respectively).

Previous work had indicated that the 2 canine hookworms, Ancylostoma caninum and Uncinaria stenocephala, may differ in their susceptibility to treatment with milbemycin oxime. Thus, the study reported here was to examine the effects of this drug on concomitant infections in experimentally infected dogs. Twenty specific-pathogen-free Beagles were inoculated orally with 500 infective-stage larvae from a mixture of larval A caninum and U stenocephala. Quantitative fecal examinations were performed weekly, beginning the day of infection. The dogs were assigned to 2 equal groups, 1 group that received the compound and 1 that received a placebo. The dogs were treated on postinoculation days 30, 60, and 90. For A caninum, egg counts dropped precipitously after the first treatment, and no eggs of this species were found in the feces of any of the treated dogs after the second treatment. The treatments had no significant effect on the mean egg counts made on U stenocephala, although 2 dogs stopped passing eggs entirely after the second treatment. At necropsy, no A caninum were found in any of the treated dogs; the mean number recovered from the control-group dogs was 56.1. Significant difference was not found in the mean number of adult U stenocephala recovered from the treated and control groups (27.0 and 21.7, respectively).

Twenty-six mixed-breed (14 males, 12 females) dogswere used in a double-blind study to evaluate the effect of milbemycin oxime against naturally acquired infection with Ancylostoma caninum. Dogs were ranked and paired, on the basis of number of hookworm eggs/g of feces, and treatment was randomly assigned. Each dog was given either the study drug or placebo (1 tablet/11.4 kg [0.5 mg/kg] of body weight). Eggs per gram of feces enumeration was done on days 3 and 7 after treatment, and dogs were euthanatized on day 7. On day 3, 5 of the 13 dogs in the milbemycin-treated group had hookworm eggs in the feces (results of the McMaster test). In these dogs, mean number of eggs per gram of feces had decreased markedly (from 5,289 to 452) and, by day 7, was 114. At necropsy, 16 A caninum adults were recovered from 2 of the milbemycin-treated dogs. On day 3, 12 of the 13 dogs in the placebo-treated group had hookworm eggs in the feces. Mean number of eggs per gram of feces in these dogs decreased slightly (from 5,243 to 2,646), but did not decrease further by day 7. A mean number of 54.4 A caninum adults was recovered from 12 of the 13 placebo-treated dogs at necropsy. Milbemycin oxime had 97.8% efficacy against A caninum. Results also indicated that milbemycin oxime may be effective against Trichuris vulpis, but not against Dipylidium caninum.

Eighteen dogs with naturally acquired helminth infections were used to evaluate the efficacy of nitroscanate against Ancylostoma caninum, Dipylidium caninum, and Trichuris vulpis. Approximately 15 minutes before treatment, the dogs were given 100 to 200 g of canned dog food. Ten dogs were treated with nitroscanate (50 mg/kg of body weight, PO), and 8 dogs were given placebo tablets PO. The dogs were euthanatized and necropsied 10 days after treatment and helminths were recovered from the small intestine and cecum. On the basis of the number of worms recovered from treated dogs vs the number recovered from control dogs, we determined the efficacy of nitroscanate to be 99.6% against A caninum, 99.8% against D caninum, and 0% against T vulpis.