Efficacy of ivermectin against gastrointestinal nematodes of cattle in Denmark evaluated by different methods for analysis of faecal egg count reduction

Abstract

The efficacy of ivermectin (IVM) against gastrointestinal nematodes in Danish cattle was assessed by faecal egg count reduction test (FECRT). Six cattle farms with history of clinical parasitism and avermectin use were included. On the day of treatment (Day 0), 20 naturally infected calves per farm (total n = 120) were stratified by initial faecal egg counts (FEC) and randomly allocated to a treatment group dosed with 0.2 mg IVM kg−1 body weight s.c. (IVM; n = 10) or an untreated control group (CTL; n = 10). Individual FEC were obtained at Day 0 and Day 14 post-treatment and pooled faeces by group were cultured to isolate L3 for detection of Ostertagia ostertagi and Cooperia oncophora by qPCR. Treatment efficacies were analysed using the recommended WAAVP method and two open-source statistical procedures based on Bayesian modelling: ‘eggCounts’ and ‘Bayescount’. A simulation study evaluated the performance of the different procedures to correctly identify FEC reduction percentages of simulated bovine FEC data representing the observed real data. In the FECRT, reduced IVM efficacy was detected in three farms by all procedures using data from treated animals only, and in one farm according to the procedures including data from treated and untreated cattle. Post-treatment, O. ostertagi and C. oncophora L3 were detected by qPCR in faeces of treated animals from one and three herds with declared reduced IVM efficacy, respectively. Based on the simulation study, all methods showed a reduced performance when FEC aggregation increased post-treatment and suggested that a treatment group of 10 animals is insufficient for the FECRT in cattle. This is the first report of reduced anthelmintic efficacy in Danish cattle and warrants the implementation of larger surveys. Advantages and caveats regarding the use of Bayesian modelling and the relevance of including untreated cattle in the FECRT are discussed.

Field evaluation of anticoccidial efficacy: A novel approach demonstrates reduced efficacy of toltrazuril against ovine Eimeria spp. in Norway

“…Previous studies investigating the effects of anticoccidials in sheep have mostly compared different drugs with respect to oocyst excretion, faecal consistency, and weight gain without calculating the efficacy of the individual drugs ( Gjerde et al, 2009 ; Le Sueur et al, 2009 ; Diaferia et al, 2013 ). The classification thresholds used in our study were based on the figures of 90% and 95% used by Geurden et al (2015) and Peña-Espinoza et al (2016) in anthelmintic studies, as there is currently no published target efficacy available for toltrazuril. The same classification targets were used by de Souza Rodrigues et al (2017) who investigated the efficacy of different toltrazuril treatment strategies in Brazil.…”

“…Confidence intervals (CIs) for the geometric mean FOCR were obtained using parametric bootstrapping with 500 iterations. The FOCRT results then enabled classification of ACE at the farm level, based on 95% CI, as “good efficacy” (lower 95% CI > 90%), “reduced efficacy” (upper 95% CI < 95%), or inconclusive (neither of the above is true), based on equivalent classifications for arithmetic mean reductions as previously used by Geurden et al (2015) and Peña-Espinoza et al (2016) in investigations of anthelmintic efficiency.…”

“…Different statistical models have been applied to improve the calculation of the estimated efficacy from FECRT results, including bootstrapping techniques, and Bayesian methods such as Markov chain Monte Carlo ( Denwood et al, 2010 ; Torgerson et al, 2014 ; Peña-Espinoza et al, 2016 ). However, challenges remain regarding the use of faecal oocyst count reduction tests (FOCRT), the (coccidial) oocyst equivalent of FECRT, for the assessment of ACE, due to extreme variation in oocyst excretion rates compared with excretion of helminth eggs.…”

Modelling anthelmintic resistance by extending eggCounts package to allow individual efficacy

“…The FECRT was established in the World Association for the Advancement of Veterinary Parasitology (WAAVP) guideline ( Coles et al, 1992 ) and is a straightforward group-based method to evaluate overall reduction of epgs. The FECRT is commonly used in practice and it has been shown to provide robust estimation of reductions in asymptotic settings ( Levecke et al, 2012 ; Peña-Espinoza et al, 2016 ; Wang et al, 2017 ). However, it neglects some of the nowadays well-accepted issues, such as aggregation of egg counts between animals ( Morgan et al, 2005 ; Dobson et al, 2012 ) and Poisson errors from sampling procedures ( Torgerson et al, 2012 ).…”

The Evaluation of Efficacy of Valbazen (Pflizer) in the Treatment of Gastro-Intestinal Tract Parasite Invasions in Beef Cattle of West Pomerania

“…The infections mostly run in a subclinical form and usually are unnoticeable, and therefore are often underestimated by farmers. It is a reasonable problem in cattle farming, as the presence of parasites in an organism may lead to a decrease in animal welfare, health status and productivity (Chattopadhyay and Bandyopadhyay 2013;Laha et al 2013;Geurden et al 2015;Peña-Espinoza et al 2016).…”