title: Anthelmintic resistance in gastrointestinal nematodes of beef cattle in the state of Rio Grande do Sul, Brazil.
abstract: Gastrointestinal nematodes resistant to anthelmintics have been reported in several regions of Brazil, and they may be associated with economic losses for the cattle industry. This study aimed to evaluate the resistance status of gastrointestinal nematodes from naturally infected beef cattle to several commercially available anthelmintics, as well as to test the efficacy of combinations of anthelmintics against multi-resistant gastrointestinal nematodes. Ten farms located in Rio Grande do Sul state were selected by: farmers' consent; extensive raising system; availability of calves aged from 7 to 9 months naturally infected by gastrointestinal nematodes; absence of anthelmintic treatment for 60 days before the study; and presence of 70-100 calves or more of both genders with ≥ 200 eggs per gram of feces (EPG) (sensitivity of 50 EPG). These calves were distributed into 10 groups (of 7-10 animals) per farm and treated with ivermectin, doramectin, eprinomectin, fenbendazole, closantel, nitroxynil, disophenol, levamisole, albendazole, or moxidectin. Feces were collected 2 days before treatment and 14 days after treatment. Additional groups of 7-10 calves were used to test six different two-drug combinations at four of the studied farms. In general terms, fenbendazole was the most effective drug, followed by levamisole, disophenol, and moxidectin. However, parasite resistance to multiple drugs was found in all herds, especially in the genera Cooperia spp., Trichostrongylus spp., and Haemonchus spp.. Some of the two-drug combinations were effective against nematode populations identified as resistant to the same compounds when used as single drugs. The most effective combinations were moxidectin + levamisole, doramectin + fenbendazole, and levamisole + closantel. In this study, parasites resistant to the main commercially available anthelmintics were found in all herds, and some combinations of two active components belonging to different chemical groups were effective against multi-drug resistant gastrointestinal nematodes.
authors.affiliation: Departamento de Medicina Veterinária Preventiva (DMVP), Centro de Ciências Rurais (CCR), Universidade Federal de Santa Maria (UFSM), 97105-900, Santa Maria, RS, Brazil. Electronic address: fernandaramos_7@yahoo.com.br.
authors.forename: Fernanda
authors.initials: F
authors.lastname: Ramos
authors.affiliation: Departamento de Medicina Veterinária Preventiva (DMVP), Centro de Ciências Rurais (CCR), Universidade Federal de Santa Maria (UFSM), 97105-900, Santa Maria, RS, Brazil.
authors.forename: Luiza Pires
authors.initials: LP
authors.lastname: Portella
authors.affiliation: Departamento de Medicina Veterinária Preventiva (DMVP), Centro de Ciências Rurais (CCR), Universidade Federal de Santa Maria (UFSM), 97105-900, Santa Maria, RS, Brazil.
authors.forename: Fernando de Souza
authors.initials: FS
authors.lastname: Rodrigues
authors.affiliation: Departamento de Medicina Veterinária Preventiva (DMVP), Centro de Ciências Rurais (CCR), Universidade Federal de Santa Maria (UFSM), 97105-900, Santa Maria, RS, Brazil.
authors.forename: Caroline Zamperete
authors.initials: CZ
authors.lastname: Reginato
authors.affiliation: Departamento de Zootecnia, UFSM, Santa Maria, RS, Brazil.
authors.forename: Luciana
authors.initials: L
authors.lastname: Pötter
authors.affiliation: Departamento de Medicina Veterinária Preventiva (DMVP), Centro de Ciências Rurais (CCR), Universidade Federal de Santa Maria (UFSM), 97105-900, Santa Maria, RS, Brazil; Programa de Pós-Graduação em Economia e Desenvolvimento, PNPD/CAPES, UFSM, Santa Maria, RS, Brazil.
authors.forename: Alfredo Skrebsky
authors.initials: AS
authors.lastname: Cezar
authors.affiliation: Departamento de Medicina Veterinária Preventiva (DMVP), Centro de Ciências Rurais (CCR), Universidade Federal de Santa Maria (UFSM), 97105-900, Santa Maria, RS, Brazil.
authors.forename: Luís Antônio
authors.initials: LA
authors.lastname: Sangioni
authors.affiliation: Departamento de Medicina Veterinária Preventiva (DMVP), Centro de Ciências Rurais (CCR), Universidade Federal de Santa Maria (UFSM), 97105-900, Santa Maria, RS, Brazil.
authors.forename: Fernanda Silveira Flores
authors.initials: FSF
authors.lastname: Vogel
mesh_terms: D015766:Albendazole / Q000627:therapeutic use; D000818:Animals; D000829:Animals, Domestic; D000969:Antinematodal Agents / Q000627:therapeutic use*; D001938:Brazil; D002417:Cattle; D002418:Cattle Diseases / Q000188:drug therapy / Q000469:parasitology*; D018432:Drug Resistance, Multiple; D004359:Drug Therapy, Combination; D005243:Feces / Q000469:parasitology; D005273:Fenbendazole / Q000627:therapeutic use; D006189:Haemonchus / Q000187:drug effects; D007411:Intestinal Diseases, Parasitic / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary*; D007422:Intestines / Q000469:parasitology*; D007559:Ivermectin / Q000031:analogs & derivatives / Q000627:therapeutic use; D007978:Levamisole / Q000627:therapeutic use; D018942:Macrolides / Q000627:therapeutic use; D009348:Nematoda / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification; D009349:Nematode Infections / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary*; D010270:Parasite Egg Count; D000069466:Red Meat / Q000469:parasitology*; D012458:Salicylanilides / Q000627:therapeutic use
chemical_list: D000969:Antinematodal Agents; D018942:Macrolides; D012458:Salicylanilides; D007978:Levamisole; D005273:Fenbendazole; D007559:Ivermectin; C023342:closantel; D015766:Albendazole; C084101:doramectin; C027837:moxidectin
keywords: Bovine; Endoparasites; FECRT; Multidrug resistance