Oxyuris equi: lack of efficacy in treatment with macrocyclic lactones.

This research highlights the inefficiency of macrocyclic lactones (moxidectin, ivermectin) in treating infections caused by Oxyuris equi – a parasitic worm – in horses, suggesting possible anthelminthic resistance.

Overview of the Study

• The research is conducted to fill in the gaps in published accounts of anthelmintic failures against Oxyuris equi, a type of parasitic worm that infects horses.
• Two cases of equine oxyurosis – the condition or disease caused by Oxyuris equi – are described in the study.
• The cases pertained to horses that persistently shed O. equi eggs despite undergoing multiple treatments of anthelminthic agents moxidectin and ivermectin. The horses were located in two different herds in Hessia, Germany.

Methodology of the Research

• The two herds containing the horses of study had different compositions and ages.
• All horses under the study had received various anthelmintic treatments in 2010 and 2011, but they continued to shed O. equi nematodes and eggs.
• The horses were treated again with moxidectin and their conditions were observed, monitored, and recorded for reoccurrence of egg shedding.

Findings from the Study

• O. equi egg shedding was detected in three of six horses within 1 to 4 weeks after treatment, demonstrating the anthelmintic ineffectiveness.
• Horses sharing the same stable and paddock with the affected horses did not yield any detection of O. equi eggs or worms, indicating that the infection wasn’t contagious among the equine group.

Significance of the Study

• This is the first report in Europe showcasing the inefficacy of commercial ivermectin compounds and the very first report proving ineffectiveness of moxidectin compounds in treating O. equi infections in horses.
• The findings suggest a potential resistance to the anthelminthic drugs or confirm an existing incomplete oxyuricidal efficacy.