Prevalence of benzimidazole-resistant small strongyles in horses in a southeastern Pennsylvania practice.

This study looked at how common benzimidazole-resistant small strongyles (a type of parasitic worm) are in horses in southeastern Pennsylvania. It found these resistant worms in most of the horses in the study and concluded that neither the de-worming practices typically used in the area nor the grassland management techniques had any effect on their presence.

About the Study

• This piece of research is a study that was carried out to establish the prevalence – i.e., how widespread it is – of benzimidazole (BZ)-resistant small strongyles in horses in a particular practice in southeastern Pennsylvania.
• The parasites termed ‘BZ-resistant’ are those that have developed resistance to the common anthelmintic (de-worming) drug, benzimidazole. In such cases, treatment with BZ proves ineffective in eliminating the parasites.
• Of the total of 342 horses surveyed, a whopping 291 had these BZ-resistant parasites.

Anthelmintic Practices and Pasture Management Factors

• The study evaluated the anthelmintic practices (practices of administering de-worming drugs) and pasture management conditions prevalent for 3 to 6 years and found that these had no correlation with the presence of BZ-resistant small strongyles.
• Even in horses treated interchangeably with BZ and non-BZ products or those receiving BZ as infrequently as just twice a year, BZ-resistant small strongyles were recovered. This indicates that the development of resistance is not strictly linked with the frequency or type of de-worming treatment being used.
• However, as the researchers noted, since the horses might have been infected with resistant small strongyles prior to the start of any particular anthelmintic treatment schedules, it was challenging to directly link BZ-resistance to any specific pattern of drug usage.

Susceptibility to BZ and Alternative Treatments

• It was observed that a small fraction of the study population (51 horses comprising 14.9%) had small strongyles susceptible to BZ.
• These horses were found to be on poor overall parasite control programs and had been given BZ drug not more than once in a year. This implies that better parasitic control and more frequent use of BZ might be linked with retaining the susceptibility of parasites to BZ.
• Finally, the study highlights that BZ-piperazine (a combination drug) and other non-BZ anthelmintic drugs were effective when used in herds infected with BZ-resistant small strongyles.