Evaluation of ivermectin for larvicidal effect in experimentally induced Parascaris equorum infections in pony foals

A controlled test was carried out on 15 pony foals inoculated with 1,500 +/- 108.8 infective Parascaris equorum eggs. The foals were assigned to 3 treatment groups. Treatments given on postinoculation day 11 included 0.2 mg of ivermectin/kg of body weight, formulated as paste (n = 5), or liquid (n = 5), or no treatment (controls; n = 5). The foals were euthanatized on postinoculation day 25, and examined for larvae in the small intestine, lungs, and liver. Larvae were not found in foals treated with ivermectin liquid or paste, whereas significantly (P less than 0.05) higher mean numbers (960.9; range, 379 to 1,736) of 4th-stage larvae were found in the controls. Histologic and gross examination of lungs and liver revealed pathologic changes attributable to P equorum migration that were similar in all foals. Adverse reactions to treatment were not observed.