The threat of reduced efficacy of anthelmintics against gastrointestinal nematodes in sheep from an area considered anthelmintic resistance-free

Antonio Bosco,Marian Varady,Laura Rinaldi,Jan Kießler,Giuseppe Cringoli,Maria Paola Maurelli,Davide Ianniello,Alessandra Amadesi,Barbara Hinney

doi:10.1186/s13071-020-04329-2

Abstract

BackgroundThe worldwide increased difficulty to combat gastrointestinal nematode (GIN) infection in sheep, due to progressing anthelmintic resistance (AR), calls for an enhanced and standardized implementation of early detection of AR. This study provides a snapshot of the current AR status against benzimidazoles and macrocyclic lactones in southern Italy, generated with standardized techniques.MethodsOn 10 sheep farms, the efficacy of albendazole (ALB) and either eprinomectin (EPR) or ivermectin (IVM) was evaluated based on the faecal egg count reduction test (FECRT) performed with the Mini-FLOTAC. For each tested drug, 40 sheep were rectally sampled at D0 and sampled again 14 days after the treatment (D14). The FECRT was calculated from individual samples and pooled samples which consist of 5 individual samples. Efficacy was classified as ‘reduced, ‘suspected’ and ‘normal’. Coprocultures were set for D0 and D14 faecal samples of each group. From farms with FECR < 95%, an in vitro egg hatch test (EHT) and a follow-up FECRT using fenbendazole (FBZ) were conducted.ResultsBased on the FECR, high efficacy (from 95.7% to 100%) was observed for ALB and IVM in eight farms (Farms 3–10). On Farm 1 and Farm 2, the efficacy for the macrocyclic lactones was classified as ‘normal’, but ‘reduced’ efficacy was observed for ALB on Farm 1 (FECR = 75%) and ‘suspected’ efficacy on Farm 2 (FECR = 93.3%) with the predominant GIN genus Trichostrongylus followed by Haemonchus at D14. The FEC results of pooled samples strongly correlated with those of individual samples, for FEC at D0 (rs = 0.984; P < 0.0001) and at D14 (rs = 0.913; P < 0.0001). The classifications of efficacy in Farm 1 (FECR = 86.0%) and Farm 2 (FECR = 93.0%) in the follow-up FECRT with FBZ coincide with the main FECRT trial. The in vitro EHT confirmed AR in both farms (Farm 1: 89%; Farm 2: 74%).ConclusionsIn regions like southern Italy, where the negative impacts from AR have played a minor role, efficient monitoring of AR is important in order to evaluate potential risks and being able to promptly respond with countermeasures.

Highlights

The worldwide increased difficulty to combat gastrointestinal nematode (GIN) infection in sheep, due to progressing anthelmintic resistance (AR), calls for an enhanced and standardized implementation of early detection of AR
Personal communication), the aim of this study was to investigate the current levels of efficacy of BZ and macrocyclic lactones (ML) in sheep in the Campania region by performing a standardized survey by the faecal egg count reduction test (FECRT) in accordance with the guidelines established in the framework of the European COST Action “COMBAR - COMBatting Anthelmintic Resistance in Ruminants”
Seven farmers used to practice regular parasitological monitoring before the anthelmintic treatment and all performed a rotation of anthelmintics using benzimidazoles and macrocyclic lactones once per year; one class was used in spring, the other class in autumn and vice versa

Summary

Introduction

The worldwide increased difficulty to combat gastrointestinal nematode (GIN) infection in sheep, due to progressing anthelmintic resistance (AR), calls for an enhanced and standardized implementation of early detection of AR. The improper use (over- and mis-use) of anthelmintics has led to development of anthelmintic resistance (AR) which is reported worldwide in multiple nematode species, especially in sheep, against multiple anthelmintic classes, e.g. benzimidazoles (BZ) and macrocyclic lactones (ML) ([3, 5,6,7,8], Hanna Rose Vineer et al in preparation). Due to the costs of anthelmintic-resistant nematode infections, there is a wide consensus on the need to enhance and implement early detection of AR based on active monitoring of the efficacy of anthelmintics in order to promptly respond to the development of AR. There are indications that some actions are able to slow down the development and spread of AR, e.g. promote “best practice” parasite management programmes based on sustainable use of anthelmintics through targeted treatment (TT) and targeted selective treatment (TST) based on easy-to-use diagnostics to inform treatment decisions [7, 9]

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