Prevalence of Parascaris equorum infection in foals on French stud farms and first report of ivermectin-resistant P. equorum populations in France.

This research article discusses the prevalence of Parascaris equorum infection, a worm that primarily affects foals, in French stud farms and provides the first report of an increasingly resistant mutation of P. equorum to a common drug, ivermectin, in France.

Understanding Parascaris equorum

• Parascaris equorum is a type of nematode which primarily infects young horses or foals. It tends to be less common and burdensome in adult horses since protective immunity typically develops around when they reach 6 months of age.
• The nematode is contracted when a horse ingests its eggs, which are typically shed in the environment by foals infected during the previous year.
• Symptoms of a P. equorum infection include respiratory issues, poor growth, diarrhoea or colic, and a rough hair coat. If a horse is heavily infected, the adult worms can cause dangerous conditions like intestinal obstruction, intussusception or even ruptures.

Prevalence of Parascaris equorum

• While the prevalence of P. equorum has been widely studied in various countries, including the USA, Germany, and Sweden where infection rates range from 22.4% to 80%, the prevalence in France has been largely unexplored.
• The primary purpose of this study was to estimate the prevalence of P. equorum in French foals on fifteen large stud farms.

Treatment and Resistance of Parascaris equorum

• In horse breeding regions, it is routine to regularly treat young horses for P. equorum infections until they are 12 months old.
• The most commonly used drugs against P. equorum come from three groups: benzimidazole compounds, tetrahydropyrimidines (pyrantel), and macrocyclic lactones (such as ivermectin and moxidectin). Macrocyclic lactones are especially important due to their broad-spectrum activity.
• However, since the first report of macrocyclic lactones treatment failure in the Netherlands in 2002, more instances of resistance to this drug class have been reported in several European countries, North America, and Brazil. In France, there have been anecdotal reports of ivermectin treatment failures in foals and weanlings.
• The secondary aim of the study was to investigate the efficacy of ivermectin in treating P. equorum infections using a faecal egg count reduction (FECR) test in three farms that had reports of resistant ascarid populations.