An oral liquid form of ivermectin was administered to 14 purebred Collies (12 rough coated, 2 smooth coated). All Collies were given ivermectin at dosages of 100 and then 200 micrograms/kg of body weight. Three of the dogs developed mild clinical signs of toxicosis (salivation, vomiting, confusion, ataxia, and tremors) with the 100 micrograms/kg dosage. After the 200 micrograms/kg dosage, 7 dogs (including 1 smooth-coated Collie) developed severe toxicosis (seizure-like activity, recumbency, nonresponsiveness, and coma). Because dogs that developed severe toxicosis were not retreated, only the 7 remaining dogs were given ivermectin at 600 micrograms/kg. Severe toxic signs were not observed in the dogs given the 600 micrograms/kg dosage, and only 1 of these 7 dogs developed severe toxicosis when given ivermectin at 2,500 micrograms/kg. Dogs that developed severe toxicosis were given supportive care while in the comatose state. All dogs recovered completely. The results indicated that Collies (including the smooth-coated Collies) have a wide range of sensitivity to ivermectin-induced toxicosis.
Eighteen pony foals inoculated with 1,500 +/- 109 infective Parascaris equorum eggs were given 0.02 ml of ivermectin vehicle (liquid)/kg of body weight, PO, (control); 0.2 mg of ivermectin paste/kg, PO; or 0.2 mg ivermectin liquid/kg, PO, on postinoculation day (PID) 28. Foals were euthanatized on PID 42, and the small intestinal contents were examined for P equorum larvae. The mean number of fourth-stage P equorum larvae in foals treated with ivermectin paste and liquid were 3.5 and 6, respectively. Significantly (P less than 0.01) higher mean numbers of larvae (1,250) were detected in foals treated with ivermectin vehicle. Larvae recovered from foals treated with ivermectin vehicle were of significantly (P less than 0.002) longer mean length than those from foals treated with ivermectin paste or liquid. Gross examination of lungs and liver revealed similar pathologic changes from the migration of P equorum in all foals. Adverse reaction to treatment was not observed.
One percent or more unembryonated eggs of Haemonchus contortus survived in sheep fecal pellets less than 0.5 hour at -95 C, 2 hours at -28 C, 1 hour at -10 C, 4 days at 4 C, and 1 hour at 45 C. One percent or more embryonated eggs survived 1 hour at -95 and -28C, 12 hours at -10 C, 64 days at 4 C, and 12 hours at 45 C. Over half the unembryonated and embryonated eggs survived only 1 and 4 days, respectively, at 4 C. One percent or more 1st-stage larvae did not survive 0.5 hour at -95 C but did survive 0.5 hour at -28 C, 8 hours at -10 C, 16 days at 4 C, and 1 hour at 45 C. Less than 1% of 2nd-stage larvae survived up to 2 days at -95 C; all were dead by 4 days. Second-stage larvae survived 32 days at -28 C, 8 days at -10 C, 64 days at 4 C, and 2 hours at 45 C. One percent or more 3rd-stage larvae survived 256 days at -95 C, 16 days at -28 C, 32 days at -10 C, more than 256 days at 4 C, 128 days at 20 C, 64 days at 25 and 35 C, and 4 days at 45 C. Thus, the increasing order of survival was unembryonated eggs, 2nd-stage larvae, 1st-stage larvae, embryonated eggs, and 3rd-stage larvae.
Twenty ponies less than 18 months of age and infected with Parascaris equorum were treated with either 0.2 mg of ivermectin/kg of body weight (n = 10) or a placebo (n = 10; controls). Five control and 5 ivermectin-treated ponies were euthanatized 14 and 35 days after treatment, respectively. At necropsy, the small intestinal contents, lungs, and liver were examined for larvae and/or adult P equorum. Significantly (P less than 0.02) higher mean total numbers of P equorum were found in the small intestinal contents of the controls on day 14 (51) and on day 35 (21) than in the ivermectin-treated ponies on days 14 (0) and 35 (3). The efficacy of ivermectin in removing adult and intestinal larvae of P equorum at 14 days after treatment was 100%. The efficacies of ivermectin in removing adults and intestinal larvae of P equorum at 35 days after treatment were 100% and 76.9%, respectively. Gross examination of liver and lung tissues revealed damage as a result of P equorum infections in all ponies. The Baermann technique used on liver and lung tissues did not yield any P equorum larvae. Adverse reactions attributable to treatment were not observed.
Twenty-four lambs of mixed breeding with mixed experimental infections of Haemonchus contortus, Ostertagia circumcincta, Trichostrongylus axei, and T colubriformis were allotted to 4 groups. One group (control) was given the vehicle propylene glycol, and the others were given 100, 200, or 300 micrograms of ivermectin/kg of body weight by mouth. Twelve days after treatment, the sheep were necropsied. The compound was greater than 99% effective against immature stages of 4 nematode species at all dosages, except at the 100 micrograms/kg dosage, where efficacy was 96% against H contortus.
Fifteen pony foals were inoculated with 1,500 +/- 298.7 infective Parascaris equorum eggs. The foals were assigned to 3 treatment groups. Treatments included 10 mg of fenbendazole/kg given once on postinoculation day (PID) 11, 10 mg of fenbendazole/kg given daily on PID 11 to 15, and no treatment (controls). The foals were euthanatized on PID 25 and examined for P equorum larvae in the small intestine, lungs, and liver. Significantly (P less than 0.05) lower mean numbers of P equorum larvae were found in the small intestine of foals treated on PID 11 to 15 (1.4 [range, 0 to 6]) than in the small intestine of foals treated on PID 11 (428.2 [range, 0 to 777]) and in controls (500 [range, 284 to 802]).
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