Resistance to benzimidazole anthelmintics in equine strongyles. 1. Frequency, geographical distribution and relationship between occurrence, animal husbandry procedures and anthelmintic usage.

This research investigated the frequency and distribution of strongyles, a type of parasitic worm, that are resistant to a specific anthelmintic drug called benzimidazole in certain regions in Australia. It was found that the resistance is widespread, varies with how often the drug is used, and is not a major issue on farms using a variety of anthelmintics in rotation and with regular intervals.

Objective and Methodology

• The study aimed to understand whether populations of strongyles, a type of equine parasitic worm, resistant to the antiparasitic drug benzimidazole are present in certain locations of Australia, their distribution and frequency, the species involved, and the relationship with varied parasite control methods and the occurrence and frequency of resistance.
• A comprehensive survey was conducted throughout different regions of New South Wales and north central Victoria.

Findings

• The study discovered resistant populations of strongyles in wide areas of New South Wales and north central Victoria.
• However, there was no direct relationship established between the geographical location and the occurrence of benzimidazole resistance.
• The resistant strongyles belonged to the sub-family Cyathostominae, commonly referred to as small strongyles.
• A direct correlation was found between the occurrence of resistance (including the degree of prevalence) and the frequency of benzimidazole anthelmintics use. This implies that the more frequently the drug was used, the more resistance was observed.

Implications and Suggestions

• Upon examining different management practices, it was found that resistance was not a major problem on farms that employed a varied and measured use of anthelmintics. This includes practicing slow rotation among different classes of anthelmintics, using combination therapy (with benzimidazole, piperazine, and organophosphates), and ensuring that anthelmintic treatments were given at intervals of no less than 16 weeks.
• The findings led to tentative suggestions for controlling small strongyles, especially in light of emerging resistance issues. It suggests that diversity and careful management of antiparasitic treatments are key in mitigating drug resistance among these parasites.