Comparison of in vitro methods and faecal egg count reduction test for the detection of benzimidazole resistance in small strongyles of horses.

This research study aimed at comparing different tests methods to detect the resistance of small strongyles, a type of horse parasite, to benzimidazole, an anthelmintic or worm treatment drug. The results indicated a considerable resistance to the drug fenbendazole in multiple horse stud farms, with variations in degrees of resistance seen in in vitro tests.

Background of the Study

• The main focus of this study was to compare three different methods for detecting benzimidazole resistance in small strongyles typically found in horses.
• These three methods are the in vitro egg hatch test (EHT), in vitro larval development test (LDT), and in vivo faecal egg count reduction test (FECR test).
• The researchers aimed to determine the presence of resistant or susceptible populations of small strongyles in 25 horse stud farms.

Study Findings and Interpretation

• The presence of resistant strongyle populations was determined using both the in vivo FECR test and in vitro EHT.
• Based on the FECR test results, fenbendazole resistance was detected in 15 out of the 25 horse stud farms, totaling to approximately 60% of the farms studied.
• The measure of resistance, represented by the ED50 value (referring to the concentration of anthelmintic required to inhibit 50% of egg hatching), varied significantly between suspected resistant populations. This varied from 0.110 to 0.222 micrograms per milliliter of thiabendazole (TBZ), another form of benzimidazole.
• An extended study using the in vitro LDT detected small strongyles populations suspected of benzimidazole resistance in 11 stud farms. These resistant populations emerged at LD50 values greater than 0.029 micrograms per milliliter of TBZ. The LD50 value here refers to the concentration of the drug needed to inhibit the development of 50% of eggs into L3 infective larvae.

Implications and Conclusion

• This study illustrates the significance of utilizing different test methods in evaluating the resistance of small strongyles to benzimidazole.
• The evidence of fenbendazole resistance in a substantial proportion of the stud farms investigated suggests a need for alternative methods of parasite control.
• The variation in the level of resistance detected by the different tests (EHT, LDT, and FECR test) provides insight into the complexity of anthelmintic resistance in small strongyles and the need to constantly monitor and adapt control strategies accordingly.