Multiple anthelmintic resistance in Southern Brazil sheep flocks.

Plínio Aguiar De Oliveira,Ana Carolina Barreto Coelho,Bianca Lemos Dos Santos,Jerônimo Lopes Ruas,Ana Lucia Schild,Marco André Paldês Costa,Beatriz Riet-Correa,Pablo Estima-Silva

doi:10.1590/s1984-29612017058

Abstract

Gastrointestinal parasites represent an important cause of reduced productivity of sheep worldwide. As anthelmintic are still the main control tool for these parasites, this work evaluated the efficacy of commercially available active principles in 22 sheep flocks in the southern region of Rio Grande do Sul, Brazil. In each farm 10 sheep were randomly distributed in seven groups with the following treatments: abamectin; albendazole; closantel; levamisole; monepantel; trichlorphon and no anthelmintic (control). All flocks showed resistance to at least three anthelmintics and in 20 farms only two products demonstrated efficacy for parasitic control. In two farms, there was no susceptibility to the six active principles tested. The results of this study provide evidence that the common commercially available anthelmintic are not assuring effective chemical control of gastrointestinal parasitic infections in ovine flocks in the southern region of Rio Grande do Sul. Monepantel, the newest introduced drug in the Brazilian market was not effective in 18% of the flocks tested, confirming that the parasitic resistance can be established quickly after the introduction of new molecules mainly when alternative program of parasite control is not performed.

Highlights

In the first decade of the 21st century, Brazil reached the status of the 17th largest sheep producer in the world, with a flock of 17.3 million head (FAO, 2012)
As anthelmintic are still the main control tool for these parasites, this work evaluated the efficacy of commercially available active principles in 22 sheep flocks in the southern region of Rio Grande do Sul, Brazil
The results of this study provide evidence that the common commercially available anthelmintic are not assuring effective chemical control of gastrointestinal parasitic infections in ovine flocks in the southern region of Rio Grande do Sul

Summary

Introduction

In the first decade of the 21st century, Brazil reached the status of the 17th largest sheep producer in the world, with a flock of 17.3 million head (FAO, 2012). There are reports that, in the state of Rio Grande do Sul, parasitic diseases represent from 24.3% to 66.8% of the diagnoses performed in sheep flocks (RISSI et al, 2010) This includes gastrointestinal parasites, a major cause of mortality and reduced productivity in small ruminants (CHARLIER et al, 2014b). In the majority of properties, anthelmintics are still the main parasitic control tool (LARA, 2013) and indiscriminate use of anthelmintics has contributed to the selection and establishment of resistant parasites (ALMEIDA et al, 2010) This fact represents one of the greatest problems for the effective control of parasites in sheep (MOLENTO, 2004; VERÍSSIMO et al, 2012), preventing the sustainability of global sheep farming (COLES et al, 2006)

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