Effectiveness of monepantel and levamisole to control gastrointestinal strongylid parasites of sheep

Anthelmintic resistance poses a major challenge to the control of endoparasites in sheep. The recent launch of monepantel may represent an alternative for the treatment of helminth infections. The purpose of this study was to assess the effectiveness of monepantel and levamisole in the sheep flock on the experimental farm Capim Branco, of the Federal University of Uberlandia, municipality of Uberlandia, state of Minas Gerais, Brazil. Thirty sheep with more than 200 eggs per gram of feces (EPG) were selected. Ten of these animals were treated orally with 2.5 mg/kg of monepantel, ten were treated subcutaneously with 7.5 mg/kg of levamisole, and ten served as control animals. Fecal samples for the determination of EPG were collected on days zero (pre-treatment), seven and fourteen (post-treatment). The percentage of effectiveness was calculated using RESO 2:01 software. Monepantel reduced the EPG of Haemonchus sp. and Trichostrongylus sp. by more than 95%, but Oesophagostomum sp. was reduced by only 50% and 33% on days seven and fourteen. The percentage reduction of EPG by levamisole remained above 95% for all the helminths recovered from fecal cultures, indicating its effectiveness. These data demonstrate the failure of monepantel to control Oesophagostomum spp. in the evaluated sheep flock.