Evaluation of tests for anthelmintic resistance in cyathostomes.

The research article speaks about the concerning emergence of resistance to anthelmintic drugs, particularly benzimidazoles (BZ), in horse cyathostomes worldwide. The article describes an evaluation of different methods to detect such resistance, highlighting the potential of the Larval Development Assay (LDA) as a promising single-visit test that might outperform traditional methods.

Objective of the Research

• The main objective was to evaluate the current tests used for identifying drug resistance in cyathostomes, a type of parasitic worm in horses, especially resistance to benzimidazoles, a class of anthelmintic drugs. The standard diagnostic tool, faecal egg count reduction (FECR) tests, have shown some limitations and potential inaccuracies. Therefore, an alternative in vitro test, the Larval Development Assay (LDA), was considered and tested in this study.

Methodology

• The study was conducted on adult horses residing on 15 different properties spread across New South Wales, Australia. The various procedures involved in the research include conducting FECR tests and LDA tests on these horses, with measurements taking place before and 10-14 days after treatment with specific anthelmintic drugs like oxibendazole, morantel, and ivermectin.
• Initial results from the FECR test were considered and low pre-treatment egg count properties were excluded from the study, narrowing the focus to seven properties which mostly revealed cyathostome larvae.

Findings

• The researchers observed and defined resistance to anthelmintic drugs as a faecal egg count reduction (FECR) of less than 90%. By using this parameter, they discovered resistance to oxibendazole on six properties and to morantel on two properties.
• No resistance to ivermectin was found.
• An alternative calculation method for FECR, based on individual horse egg counts pre- and post-treatment was also developed and tested within the study. The correlation coefficients of values between lethal concentration to kill 50% of the population during the LDA test and FECR percentages were comparatively examined, particularly before and after treatment with Benzimidazoles.

Conclusions

• Based on their findings, the researchers concluded that the Larval Development Assay (LDA) could potentially serve as a more effective single visit detection mechanism for anthelmintic resistance in horse cyathostomes. However, they also indicated that further investigations and standardization studies would be needed to fully validate this diagnostic method.