Assessing the benzimidazole resistance in equine strongyles by in vitro methods.

The research article is about a study conducted to determine the level of resistance to benzimidazole (BZ) among strongyles, a type of equine parasite, using in vitro tests. The researchers also sought to identify early indicators of resistance to help facilitate better parasite management on horse farms.

Objective and Methodology

• The study aimed to measure the occurrence of benzimidazole (BZ) resistance in strongyles, a common type of equine parasite. BZ is a widely-used drug for treating parasite infestations, so understanding the level of resistance is important for effective parasite management.
• The researchers used in vitro egg hatch test (EHT) and larval development test (LDT) to assess the resistance. These tests involved measuring the amount of BZ, specifically a derivative called thiabendazole (TBZ), required to halt egg hatching and larval development.
• Fecal samples from 203 horses across 8 farms were collected for the study, and 77 horses were selected for in vitro testing based on specific criteria.
• Additionally, 18 horses were chosen to compare the results of the in vitro tests with the in vivo fecal egg count reduction test (FECRT), another commonly used method to assess parasite resistance.

Findings

• The results of the EHT indicated that resistant strongyles were present on all 8 farms tested. For over half of the horses, the TBZ concentration threshold of 0.1 μg/ml, beyond which resistance is considered present, was exceeded.
• The percent of egg hatch varied greatly amongst resistant parasites, from 39.0 ± 6.0% to 91.0 ± 1.0% at the 0.1 μg/ml TBZ concentration. This suggested different levels of resistance within the population.
• In the LDT, the average TBZ concentration needed to stop the development of 50% and 99% larvae to the infective stage was 0.0753 ± 0.0454 and 0.6798 ± 1.9144 μg/ml TBZ, respectively.
• There was no significant statistical agreement between the results of EHT, LDT and the in vivo FECRT. This implies that these tests might measure different aspects of resistance and thus, should be interpreted differently.

Conclusion

• The researchers concluded that in vitro EHT could be used as an indicator for early BZ resistance detection. They also suggested that monitoring the egg hatching process at specific concentrations could help in detecting and estimating the proportion of the resistant parasite population on horse farms, contributing to better equine health management.