Adaptation of a 96-well plate larval migration inhibition test for measuring the sensitivity of cyathostomins to macrocyclic lactone anthelmintics.

This research article focuses on the development and adaptation of a more sensitive testing method to detect resistance to macrocyclic lactone drugs in equine cyathostomins. Traditional methods like the faecal egg count reduction test have proven quite insensitive, prompting the development of a 96-well plate larval migration inhibition test.

Study Rationale and Approach

• Cyathostomins, common parasites in horses, are becoming increasingly resistant to macrocyclic lactone drugs such as ivermectin and eprinomectin, traditionally used for their control. The purpose of the study was to refine a more sensitive method to detect this drug resistance.
• The researchers utilized an already existing method known as the larval migration inhibition test but modified it to suit a 96-well plate setup for higher throughput. This modified method provided more precise results regarding the parasites’ sensitivity to the aforementioned drugs.

Methodology and Findings

• The setup conditions for the test were optimized to allow for proper larval migration. The team also studied the effect of varying storage times of the larvae on the drug dose responses.
• Using this refined method, the sensitivity of different Cyathostomin isolates to ivermectin and eprinomectin was distinctively defined by analyzing dose-response curves and calculating half maximal inhibitory concentration (IC) values – a measure of the drugs’ effectiveness.
• Interestingly, these IC values proved to be more consistent compared to using larvae stored for varying periods before the test.

Limitations and Recommendations

• The study identified certain limitations such as the variability in the control-well migration even after optimizing incubation conditions. Also, there was a need to determine the specific species composition in the larval populations, as drug sensitivity could differ among different cyathostomin species.
• Further validation of this testing technique is required using both susceptible and resistant isolates of known species compositions to fully establish its effectiveness and reliability.

The results from this study suggest that the modified 96-well plate larval migration inhibition test could potentially be a useful tool in detecting drug resistance among cyathostomins and possibly other parasites. However, further research and confirmatory studies are needed.