Lack of efficacy of monepantel against trichostrongyle nematodes in a UK sheep flock

Abstract

Monepantel resistance was diagnosed during routine monitoring of the effectiveness of a farm's roundworm control strategy. Weaned lambs had become ill thrifty and developed diarrhoea, despite the routine use of monepantel. This clinical presentation was caused by trichostrongylosis. The faecal egg count reduction was 76.7% (95% CI: 55.1-82.2%) following treatment with 2.5 mg/kg monepantel. Predominantly Trichostrongylus vitrinus along with small proportions of Oesophagostomum venulosum and Trichostrongylus vitrinus were identified by deep amplicon sequencing of pools of larvae recovered from pre and post monepantel treatment coprocultures and on postmortem examinations. The undifferentiated FECRT showed resistance to monepantel, but not to levamisole, ivermectin, or moxidectin. Examination of farm anthelmintic treatment and animal movement records suggested that treatments before movement onto silage aftermaths, putatively with low numbers of susceptible nematodes in refugia, may have placed a high selection pressure on monepantel resistance. Effective control of parasitic gastroenteritis using anthelmintic drugs is a prerequisite for sustainable sheep production. This case reiterates the need for care when combining anthelmintic treatments with movements to safe grazing, and the value of monitoring of anthelmintic efficacy as part of iterative planned animal health management.

Teladorsagia circumcincta beta tubulin: the presence of the E198L polymorphism on its own is associated with benzimidazole resistance

“…2 Departamento de Sanidad Animal, Facultad de Veterinaria, Universidad de León, Campus de Vegazana, 24071 León, Spain. 3 Departmento de Ciencias Biomédicas, Facultad de Veterinaria, Universidad de León, 24071 León, Spain. 4 Instituto de Salud Global de Barcelona (ISGlobal), Barcelona, Spain.…”

Phylogenetic analysis of Trichostrongylus vitrinus isolates from southwest Iran

“…There is only one Iranian, drug resistance study from Khuzestan Province the neighboring region of Kohgiloyeh and Boyerahmad Province and this showed a higher levamisole drug resistance of T. vitrinus compared to other Trichostrongylus species in sheep flocks [ 40 ]. A recent study in the UK also showed T. vitrinus as the sole Trichostrongylus species with monepantel resistance in a sheep/cattle farm [ 46 ]. Another study revealed higher anti-helminthic resistance and higher prevalence of T. vitrinus in treated livestock in comparison to other species including T. colibriformis and T. axei in Scotland [ 9 ].…”

Implication of the fecal egg count reduction test (FECRT) in sheep for better use of available drugs

“…However, previous testing is always necessary, as resistance of Trichostrongylus spp. has already been reported even to new drugs such as monepantel, for example (CINTRA et al, 2016;HAMER et al, 2018).…”

“…Constant research focuses on parasite management approaches aimed at lowering AHR, such as methods of selective control (CHAGAS et al, 2016), pasture management systems (BURKE et al, 2009), refuge management (MUCHIUT et al, 2018) and selection of parasite resistant animals (AGUERRE et al, 2018). Nevertheless, at some point, AH are inevitably needed for the effective control of parasitic gastroenteritis (HAMER et al, 2018).…”