Field effectiveness of pyrantel and failure of Parascaris equorum egg count reduction following ivermectin treatment in Italian horse farms.

The study investigates the effectiveness of ivermectin and pyrantel pamoate in treating Parascaris equorum in horses on Italian farms. It found that treatment varied, with ivermectin showing effectiveness in some cases, but pyrantel pamoate consistently effective in all instances.

Research Methodology

The research included 73 foals aged between three to 18 months selected from five stud farms. To be included, the foals must not have been treated with anthelmintics in the preceding ten weeks and had individual faecal egg counts (FEC) over 200. At each farm:

• 5-7 foals were treated with ivermectin
• 5-7 foals were treated with pyrantel pamoate
• 3 foals were left untreated as control samples

Both medicines were delivered at specific dosages based on body weight, and faecal egg counts were carried out before treatment and on subsequent seventh and twenty-first days.

Assessment of Efficacy

The researchers used multiple previously suggested formulae to assess the percent reduction of FECs. They carried out a bootstrap simulation – a method of statistical resampling, to provide an individually-based estimation of the treatment’s efficacy. Two thousand bootstrap resamples were constructed from individual FECRs (Faecal Egg Count Reduction).

The researchers classified the parasite populations based on FECs and accompanying confidence intervals:

• FEC > 90% and Confidence Interval > 95% were considered susceptible
• FEC between 80% to 90% and Confidence Interval < 95% were considered as suspected resistant
• FEC≤80% and Confidence Interval < 90% were listed as resistant

Research Findings

The study’s analysis found that the effectiveness of the Ivermectin varied. On two farms, it was effective; on one, it resulted in ambiguous results, and on two farms, it proved ineffective. However, Pyrantel pamoate showed full effectiveness on all farms. This suggests the existence of Parascaris equorum populations resistant to Ivermectin in Italy, hinting at a widespread resistance trend through Europe’s horses.