Evaluation of the effect of simulated rainfall on the efficacy of Ivomec Pour-On against Cooperia spp. infection in cattle

Confounding factors affecting faecal egg count reduction as a measure of anthelmintic efficacy

Increasing anthelmintic resistance (AR) in livestock has stimulated growing efforts to monitor anthelmintic effectiveness (AE) on livestock farms. On-farm assessment of AE relies on measuring the reduction in faecal egg count (FEC) following treatment; and if conducted rigorously, qualifies as a formal FEC reduction test (FECRT) for AR. Substantial research effort has been devoted to designing robust protocols for the FECRT and its statistical interpretation; however, a wide range of factors other than AR can affect FEC reduction on farms. These are not always possible to control, and can affect the outcome and repeatability of AE measurements and confound the on-farm classification of AR using FECRT. This review considers confounders of FEC reduction, focusing on gastrointestinal nematodes of ruminants, including host and parasite physiology and demography; pharmacokinetic variation between drugs, parasites and hosts; and technical performance. Drug formulation and delivery, host condition and diet, and seasonal variation in parasite species composition, can all affect AE and hence observed FEC reduction. Causes of variation in FEC reduction should be attenuated, but this is not always possible. Regular monitoring of AE can indicate a need to improve anthelmintic administration practices, and detect AR early in its progression. Careful interpretation of FEC reduction, however, taking into account possible confounders, is essential before attributing reduced FEC reduction to AR. Understanding of confounders of FEC reduction will complement advances in FECRT design and interpretation to provide measures of anthelmintic efficacy that are both rigorous and accessible.

Which larvae are they? Use of single larva for the molecular confirmation of Cooperia pectinata and Cooperia punctata in Australian cattle

In Australia, Cooperia spp. are often overshadowed by parasites believed to be more pathogenic production-limiting nematodes. A rise in anthelmintic resistance and reports of reduced growth rates attributed to infection with Cooperia spp. in Europe increases the need to be able to monitor the presence of C. pectinata, C. punctata and C. oncophora in Australian cattle. Here, we present the first molecular confirmation of C. pectinata and C. punctata in Australian cattle using ITS2 rDNA and COXII mtDNA. Cultured larvae were morphologically differentiated to the genus level with the aid of iodine solution and their DNA was screened using a cattle nematode MT-PCR panel. By isolating individual iodine stained and morphologically identified nematode larvae, we demonstrated the presence of C. pectinata and C. punctata using a generic ITS2 rDNA qPCR assay following DNA amplicon sequencing. A novel suite of COXII mtDNA species/genus-specific PCR assays for Cooperia speciation from complex nematode samples enabled us to detect all three species (C. oncophora, C. pectinata, C. punctata) in Australia cattle samples. Our approach, utilising traditional techniques coupled with the manipulation of individual nematode larvae, provides a foundation for the inclusion of Cooperia spp. into existing high throughput molecular diagnostic panels for cattle nematode surveillance.