Evaluation of ivermectin at an elevated dose against encysted equine cyathostome larvae.

This research study examines the impact of a high dosage of ivermectin on equine cyathostome larvae in adult ponies. The study finds that while ivermectin effectively reduces adult cyathostomes and lumenal cyathostome larvae numbers, it has a negligible impact on encysted equine cyathostome larvae.

Objective of the Research

• The goal of the research was to assess the effectiveness of a high dosage of ivermectin (1.0 mg per kg Eqvalan liquid drench) on encysted cyathostomes (a type of parasite) in adult ponies. In particular, the researchers aimed to understand how ivermectin affects the numbers of different forms of cyathostomes, including lumenal larvae, adults, and encysted larvae.

Research Methodology

• The controlled study included 12 adult ponies, all of which had naturally acquired cyathostome infections. Six ponies received the treatment (ivermectin), while the other six served as non-treated controls.
• Each group of ponies was kept in separate stalls for a period of 5 weeks. The cyathostome burdens in each pony, which included lumenal larvae, adults, and encysted larvae, were determined at necropsy. Necropsy is a post-mortem examination performed on an animal to determine cause of disease or death.
• The researchers used mural transillumination and histologic observations of 12 larvae per pony to assess the viability of the encysted larvae, based on their morphologic integrity.

Findings of the Study

• The research found that ivermectin was remarkably effective against adult cyathostomes, achieving an efficacy rate of 99.9%. The number of lumenal cyathostome larvae was also reduced, by 87%.
• In contrast, the impact of ivermectin on encysted cyathostome larvae was minimal. The numbers of these larvae, identified by transillumination of the large intestine, declined by only 35%. More importantly, this reduction was not statistically significant (P > 0.05), meaning that the difference could be due to chance.
• In addition, no differences in the viability of encysted larvae were observed as a result of the ivermectin treatment.

Conclusions of the Study

• The researchers concluded that ivermectin, while effective against adult and lumenal cyathostomes, has little demonstrable effect on encysted cyathostomes in adult ponies. This conclusion is based on both the insignificant reduction in the number of encysted larvae and the lack of observed changes in their viability.