Comparison of calculation methods used for the determination of anthelmintic resistance in sheep in a temperate continental climate

Abstract

This study compared results obtained with five different fecal egg count reduction (FECR) calculation methods for defining resistance to ivermectin, fenbendazole, and levamisole in gastrointestinal nematodes of sheep in a temperate continental climate: FECR1 and FECR2 used pre- and posttreatment fecal egg count (FEC) means from both treated and control animals, but FECR1 used arithmetic means, whereas FECR2 used geometric means; FECR3 used arithmetic means for pre- and posttreatment FECs from treated animals only; FECR4 was calculated using only arithmetic means for posttreatment FECs from treated and control animals; and FECR5 was calculated using mean FEC estimates from a general linear mixed model. The classification of farm anthelmintic resistance (AR) status varied, depending on which FECR calculation method was used and whether a bias correction term (BCT, i.e., half the minimum detection limit) was added to the zeroes or not. Overall, agreement between all methods was higher when a BCT was used, particularly when levels of resistance were low. FECR4 showed the highest agreement with all the other FECR methods. We therefore recommend that small ruminant clinicians use the FECR4 formula with a BCT for AR determination, as this would reduce the cost of the FECRT, while still minimizing bias and allowing for comparisons between different farms. For researchers, we recommend the use of FECR1 or FECR2, as the inclusion of both pre- and posttreatment FECs and use of randomly allocated animals in treatment and control groups makes these methods mathematically more likely to estimate the true anthelmintic efficacy.

Evaluation of parasite resistance to commonly used commercial anthelmintics in meat goats on humid subtropical pasture

“…The only differences amongst the equations were minor re-rankings that affected which treatment differed from LEV for relative efficacy. Some studies have found different results for resistance based on equation (Falzon et al, 2014;Pena-Espinosa et al, 2014). This was suggested to be because of a lower level of resistance to the anthelmintics tested.…”

“…This was suggested to be because of a lower level of resistance to the anthelmintics tested. The equation that is the most accurate for determining anthelmntic resistance remains undetermined and is an area of investigation (Calvete and Uriarte, 2013;McKenna, 2013McKenna, , 2014Falzon et al, 2014;Pena-Espinosa et al, 2014).…”

“…The most common way to test for anthelmintic resistance is the Fecal Egg Count Reduction Test (Calvete and Uriarte, 2013;McKenna, 2014). There are different equations used to determine anthelmintic resistance and the most effective is still debated (McKenna, 2013;Falzon et al, 2014).…”

Anthelmintic resistance in gastrointestinal nematodes of alpacas (Vicugna pacos) in Australia

“…Data validation and cleaning were performed by using Microsoft Excel 2013. Calculation of faecal egg count reduction (FECR) was performed using the contributed R package “e ggsCount ” [ 23 ] and following the WAAVP guidelines [ 19 , 24 ]. FECR (%) was calculated between treatment and control group at post-treatment collection for each anthelmintic.…”

Eficacia del monepantel para el control de aislamientos de Haemonchus contortus y Trichostrongylus spp con resistencia múltiple (ivermectina y febendazole) en caprinos

“…En las experiencias A y B, la clasificación taxonómica de las larvas obtenidas en los coprocultivos pretratamiento indicó la presencia casi exclusiva de Haemonchus contortus (98%) y el resto perteneciente al género Trichostrongylus spp., mientras que en la experiencia C la participación relativa de estos géneros fue de 78 % y 22 %, respectivamente. Debido a que existen algunas evidencias conflictivas sobre que fórmula utilizar para determinar la eficacia de los antihelmínticos cuando se utiliza el TRCH (Falzon et al, 2015), en la presente experiencia y para asegurar la interpretación de los resultados se utilizaron tres fórmulas distintas, no observándose diferencias significativas entre las mismas. Los tratamientos resultaron en reducciones del hpg utilizando las diferentes fórmulas que variaron entre el 99,7% y100% para las tres experiencias.…”