Assessment of the efficacy of commercial anthelmintics in horses naturally infected with gastrointestinal nematodes

Abstract

The objective of this study was to assess the efficacy of commercial anthelmintics in horses naturally infected with gastrointestinal nematodes from the southern Rio Grande do Sul state, Brazil. The anthelmintic efficacy was assessed by fecal egg count reduction test (FECRT) and coproculture. Fecal samples were collected from 110 animals in seven farms located in the southern region of the state of Rio Grande do Sul, in the south of Brazil. Criteria used to suspect anthelmintic resistance included percentages of efficacy lower than 95% and a lower limit of the confidence interval below 90%. Anthelmintic resistance was detected in five of the seven farms studied. Coproculture results show that, even after horses were treated with anthelmintics, infection by nematodes of the subfamily Cyathostominae was still present in animals from five farms.

Anthelmintic resistance in equine nematodes: Current status and emerging trends

“…It is remarkable that Table 1 contains six Brazilian studies reporting macrocyclic lactone resistance, which is almost half of all studies reporting resistance to this anthelmintic class. Several of these studies documented clearly reduced macrocyclic lactone efficacy in several groups and to several members of this class ( Toscan et al, 2012 ; Flores et al, 2020 ; Martins et al, 2021 ; Lignon et al, 2021 ), and one of them was a terminal study with intestinal worm counts confirming resistance to ivermectin in two cohorts ( Felippelli et al, 2015 ), providing strong evidence for these findings. In 2020, we documented the first case of macrocyclic lactone resistance in equine strongylids in the US ( Nielsen et al, 2020 ).…”

“…Thus, X means that resistance was tested, but not found, and X-AR means that resistance was tested and found. Country Publication Benzimidazoles Pyrimidines Macrocyclic lactones Algeria Boulkaboul et al (2006) X-AR X Australia Pook et al (2002) X-AR X-AR X Abbas et al (2021) X-AR X-AR Belgium Dorny et al (2000) X-AR X-AR Brazil Toscan et al (2012) X-AR Canever et al (2013) X-AR X-AR X-AR Felippelli et al (2015) X-AR Saes et al (2016) X-AR X Vera et al (2020) X-AR X Flores et al (2020) X-AR X-AR X-AR Martins et al (2021) X-AR X-AR Lignon et al (2021) <...…”