Cambendazole for strongyle control in a pony band: selection of a drug-resistant population of small strongyles and teratologic implications.

This research article presents a study examining the effectiveness of the drug Cambendazole (CBZ) for controlling strongyles, a type of parasitic worm, in ponies, as well as its potential impact on foal development. Over a four-year period, researchers found that CBZ could initially eliminate 92-96% of worm eggs, but this efficacy decreased over time, with certain species of small strongyles developing resistance.

Research Objectives and Methodology

• The primary objective of the study was to understand the effectiveness of CBZ in controlling strongyles concentration in ponies over a four-year period (1974 to 1978).
• A secondary objective was to explore the potential impacts of CBZ on foal gestation and development.
• CBZ was administered to a group of ponies every eight weeks, with worm egg counts in feces used to measure the effectiveness of the treatment.

Findings on the Effectiveness of Cambendazole

• The treatment was initially very effective, resulting in a reduction of strongyles eggs by 92-96%.
• However, the effectiveness of the drug decreased over time. By the ninth treatment, 18 months into the research, it dropped to 70%. At the 12th treatment, the rate of reduction was only 28%, and it fluctuated between 0% and 38% thereafter.
• When exploring the effectiveness against specific types of strongyles, the researchers found that the drug was successful in eliminating large strongyles species. However, they noticed resistance in five species of small strongyles.
• Interestingly, more drug-dose did not increase efficacy against the CBZ-resistant species of small strongyles, but a 4-fold increase small strongyles was found to remove 93% of the resistant small strongyles.

Implications on Foal Development

• The research team also tracked foaling rates during the study, which fluctuated between 38% and 61%.
• They observed three cases of deformed foals born during the study period; however, they were unable to establish a clear link between these deformations and the CBZ treatment periods.

Summary

• The research reveals that while initial uses of CBZ drastically reduces the strongyle parasite population in ponies, continued usage results in a decrease in the drug’s efficacy due to the development of resistance in certain species of small strongyles.
• Concerning foal gestation and birth, the findings suggest that CBZ usage does not necessarily affect foaling rates, and while deformations were observed, a concrete causative link to CBZ was not established.