Increasing resistance to multiple anthelmintic classes in nematodes including Haemonchus contortus on sheep farms in Southwest England.

K Bull,M J Glover,H Rose Vineer,E R Morgan

doi:10.31220/agrirxiv.2021.00038

K Bull, M J Glover + Show 2 more

Open Access

https://doi.org/10.31220/agrirxiv.2021.00038

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Abstract

Abstract Background: Anthelmintic resistance (AR) in gastrointestinal nematodes (GIN) is increasing globally and farmers are encouraged to adopt sustainable control measures. Haemonchus contortus is increasingly reported in the UK, potentially complicating effective GIN control. Methods: Faecal egg count reduction tests (FECRT) were conducted on 13 farms in North Devon, England, UK in 2016. Relative abundance of H. contortus was quantified using peanut agglutinin (PNA) staining and used to estimate faecal egg count reduction percentages (FECR%) using the egg Counts R package. Results: On average, farms had GIN resistance to three anthelmintic classes. No farms had susceptibility to all anthelmintics tested. AR was more prevalent in 2016 than on the same farms in 2013. Haemonchus contortus was present on 85% of the farms tested and comprised on average 6% (0-52%) of GIN eggs before treatment. Resistance or suspected resistance was observed in this species to all anthelmintics tested, on different farms. Conclusion: The results demonstrate diversity of AR profiles on farms, progression of anthelmintic resistance within a 3-year period, and challenges detecting AR in mixed species infections. Where possible, interpretation of mixed-species FECRT should take into account the relative abundance of species pre- and post-treatment to identify pragmatic treatment options targeting individual genera.

Highlights

Reduced anthelmintic efficacy against gastrointestinal nematodes (GIN) in sheep has been reported worldwide, and the presence of heritable resistance confirmed for all widely available anthelmintic classes [1, 2, 3, 4, 5, 6, 7]
Around €38 million is attributed to anthelmintic resistance (AR), through the costs of wasted treatments and production loss in animals treated with ineffective anthelmintics [14], This figure is undoubtedly rising as AR becomes more common [7]
Egg counts for the faecal egg count reduction tests (FECRTs) were conducted using a mini-FLOTAC method sensitive to 5 eggs per gram (EPG) [28], with modifications used to ensure an accurate ratio of faeces:flotation solution

Summary

Introduction

Reduced anthelmintic efficacy against gastrointestinal nematodes (GIN) in sheep has been reported worldwide, and the presence of heritable resistance confirmed for all widely available anthelmintic classes [1, 2, 3, 4, 5, 6, 7]. Understanding which anthelmintics are effective on a sheep holding is key to successfully implementing sustainable nematode control strategies. Among helminths of small ruminants, Haemonchus contortus is a pathogenic blood feeding gastrointestinal nematode (GIN) with global distribution [11]. Infection with H. contortus can cause severe anemia leading to condition loss, reduced productivity and eventually death [12, 13]. Helminth infections, including H. contortus, are responsible for huge economic loss, estimated most recently for the European ruminant livestock industry at €1.8bn per year [14]. Around €38 million is attributed to anthelmintic resistance (AR), through the costs of wasted (ineffective) treatments and production loss in animals treated with ineffective anthelmintics [14], This figure is undoubtedly rising as AR becomes more common [7]

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