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

TY - JOUR

T1 - Field evaluation of anticoccidial efficacy

T2 - A novel approach demonstrates reduced efficacy of toltrazuril against ovine Eimeria spp. in Norway

AU - Odden, Ane

AU - Denwood, Matthew J.

AU - Stuen, Snorre

AU - Robertson, Lucy J.

AU - Ruiz, Antonio

AU - Hamnes, Inger Sofie

AU - Hektoen, Lisbeth

AU - Enemark, Heidi L.

PY - 2018/8/1

Y1 - 2018/8/1

N2 - Ovine Eimeria spp. infections cause reduced welfare, increased mortality, and substantial economic losses, and anticoccidials are crucial for their control. Recent reports of toltrazuril resistance in pigs, and anecdotal reports of reduced anticoccidial efficacy in lambs, necessitate evaluation of anticoccidial efficacy. Due to the substantial lifecycle differences between nematodes and coccidia, current WAAVP methods for assessing anthelmintic efficacy are not suitable for such evaluations. Faecal samples were collected from 8 pairs of twin lambs from 36 Norwegian sheep farms 6–8 days after turnout. One twin of each pair was then treated with 20 mg/kg toltrazuril and a second faecal sample from all lambs was collected 7–11 days later. Oocyst excretion rate in all samples was determined using McMasters. Suitability of treatment timing was investigated by evaluating the increase in mean log oocyst excretion in untreated lambs. Based on comparisons between groups, a threshold of ≥0.75 (13 farms) was used to identify farms where drug efficacy could be assessed with confidence, drug efficacy on farms with increases of ≥0.5 but <0.75 (7 farms) were evaluated with caution, and drug efficacy on farms with increases of <0.5 (16 farms) was not estimated. Reduction in oocyst excretion between samples from treated lambs compared with controls from the 20 farms with a threshold of ≥0.5 were then analysed using a generalised linear mixed model. The results were classified based on 95% CI obtained using parametric bootstrapping. Among these 20 farms, two exhibited reduced drug efficacy (upper 95% CI < 95%), 13 had good efficacy (lower 95% CI > 90%), and for 5 the results were inconclusive. This is the first evidence-based report of reduced anticoccidial efficacy in ovine Eimeria spp. Additionally, we highlight the problem of sub-optimal timing of treatment (16/36 farms), which could potentially result in incorrect conclusions being reached regarding lack of drug efficacy.

AB - Ovine Eimeria spp. infections cause reduced welfare, increased mortality, and substantial economic losses, and anticoccidials are crucial for their control. Recent reports of toltrazuril resistance in pigs, and anecdotal reports of reduced anticoccidial efficacy in lambs, necessitate evaluation of anticoccidial efficacy. Due to the substantial lifecycle differences between nematodes and coccidia, current WAAVP methods for assessing anthelmintic efficacy are not suitable for such evaluations. Faecal samples were collected from 8 pairs of twin lambs from 36 Norwegian sheep farms 6–8 days after turnout. One twin of each pair was then treated with 20 mg/kg toltrazuril and a second faecal sample from all lambs was collected 7–11 days later. Oocyst excretion rate in all samples was determined using McMasters. Suitability of treatment timing was investigated by evaluating the increase in mean log oocyst excretion in untreated lambs. Based on comparisons between groups, a threshold of ≥0.75 (13 farms) was used to identify farms where drug efficacy could be assessed with confidence, drug efficacy on farms with increases of ≥0.5 but <0.75 (7 farms) were evaluated with caution, and drug efficacy on farms with increases of <0.5 (16 farms) was not estimated. Reduction in oocyst excretion between samples from treated lambs compared with controls from the 20 farms with a threshold of ≥0.5 were then analysed using a generalised linear mixed model. The results were classified based on 95% CI obtained using parametric bootstrapping. Among these 20 farms, two exhibited reduced drug efficacy (upper 95% CI < 95%), 13 had good efficacy (lower 95% CI > 90%), and for 5 the results were inconclusive. This is the first evidence-based report of reduced anticoccidial efficacy in ovine Eimeria spp. Additionally, we highlight the problem of sub-optimal timing of treatment (16/36 farms), which could potentially result in incorrect conclusions being reached regarding lack of drug efficacy.

KW - Anticoccidial efficacy

KW - Drug resistance

KW - Eimeria spp.

KW - Field evaluation

KW - Norway

KW - Sheep

U2 - 10.1016/j.ijpddr.2018.05.002

DO - 10.1016/j.ijpddr.2018.05.002

M3 - Journal article

C2 - 29777962

AN - SCOPUS:85047102439

SN - 2211-3207

VL - 8

SP - 304

EP - 311

JO - International Journal for Parasitology: Drugs and Drug Resistance

JF - International Journal for Parasitology: Drugs and Drug Resistance

IS - 2

ER -