Development of the larval migration inhibition test for comparative analysis of ivermectin sensitivity in cyathostomin populations.

The research article focuses on the development and analysis of a larval migration inhibition test (LMIT) that measures sensitivity of cyathostomin populations, a common parasitic pathogen in horses, to the veterinary drug Ivermectin (IVM).

Understanding Cyathostomins and IVM

• Cyathostomins are a type of nematode, or roundworm, and are the most prevalent parasitic pathogens found in equids (horses, donkeys, and related animals) across the globe. They have been traditionally controlled using anthelmintics, a type of drug designed to combat worm infestations.
• Ivermectin is a common broad-spectrum anthelmintic. However, resistance against multiple types of these drugs, including IVM, has been reported amongst cyathostomin populations. Therefore, identifying sensitivity or resistance to these drugs is critical in determining effective treatment plans for infected equids.

Traditional Detection: FECRT

• The most common method used to detect anthelmintic sensitivity has been the faecal egg count reduction test (FECRT). This test measures changes in the number of eggs found in faeces following treatment to assess the effectiveness of the drug.
• While the FECRT is widely used, it has been subject to significant variation and it is relatively time-consuming to execute, making it less efficient and reliable as a testing method.

Development and Assessment of LMIT

• To overcome the limitations of FECRT, the researchers developed a Larval Migration Inhibition Test (LMIT) with the objective to assess Ivermectin sensitivity in cyathostomin populations.
• The LMIT measures the paralysing effect of Ivermectin on the ability of the third-stage larvae (L3) of cyathostomins to migrate through a pore mesh. Decreased mobility suggests greater sensitivity to IVM, while increased mobility implies resistance.
• Initial testing revealed that variations in larval migration were associated with the duration the L3 had been stored prior to testing. However, the association was not significant enough to affect the overall test results.

Comparison of LMIT and FECRT

• The researchers then obtained half maximal effective concentration (EC50) values for cyathostomin L3 from six different populations that displayed varying sensitivity to IVM based on previous FECRTs.
• Populations deemed IVM-resistant by FECRT showed significantly higher EC50 values in the LMIT than those classified as IVM-sensitive or those with limited previous exposure to IVM.
• The timing of IVM treatment also appeared to affect EC50 values. For one population, a longer time since treatment was associated with lower EC50 values. As such, further consideration of this factor may be required during testing.

Conclusion

• The study’s results suggest that the LMIT provides valuable data on IVM sensitivity amongst different cyathostomin populations.
• The test does have various factors that need to be considered for its successful application and accurate interpretation of results, however, it presents significant potential for more efficient and reliable assessment of anthelmintic resistance.