Evaluation of ivermectin against later fourth-stage Strongylus vulgaris in ponies at two and five weeks after treatment.

This research assesses the potency of a drug called ivermectin, used to counteract a specific larval stage of the Strongylus vulgaris parasite in pony foals. The study defines the degree of efficacy of the drug at 14 and 35 days after application, highlighting that the drug was more effective after a longer period.

Study Methodology

• The study used pony foals that had been reared in parasite-free environments.
• The foals were infected with 500 infective larvae of Strongylus vulgaris.
• 56 days after the foals were infected, they were treated with either ivermectin with a dosage of 200 micrograms per kilogram of weight, or a placebo. The method of delivery was intramuscular injection.

Efficacy of Ivermectin

• The authors found that ivermectin was highly effective, with an efficacy rate of 98.6%, against later fourth-stage larvae in five foals that were assessed 35 days after treatment.
• However, the treatment was not as effective (72.5% efficacy) on the same larval stage in another group of five foals examined at 14 days post-treatment.

Larvae Location and Condition

• In some cases, larvae were found in the tunica media of the ileocolic arteries, which suggests these parasites were able to infiltrate the circulatory system and embed themselves in the arterial walls.
• Although the found larvae seemed to maintain their normal form, there were signs of degeneration, indicating that the larvae were either dying or already dead, most likely as a result of the ivermectin treatment.
• The researchers highlighted the need for further investigation into how the larvae got into that particular site and the potential consequences of their presence there.