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Multiple resistance to anthelmintics by Haemonchus contortus and Trichostrongylus colubriformis in sheep in Brazil

Multiple resistance to anthelmintics by Haemonchus contortus and Trichostrongylus colubriformis in sheep in Brazil,10.1016/j.parint.2010.09.006,Parasi

Multiple resistance to anthelmintics by Haemonchus contortus and Trichostrongylus colubriformis in sheep in Brazil   (Citations: 4)
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The objective of this study was to determine the level of resistance of Haemonchus contortus and Trichostrongylus colubriformis in sheep to levamisole, albendazole, ivermectin, moxidectin, closantel and trichlorfon. The parasites were isolated from sheep naturally infected by gastrointestinal nematodes and were then kept in monospecifically-infected lambs for production of infective larvae (L3) of both species. Forty-two lambs, at three months of age, were simultaneously artificially infected with 4000 L3 of H. contortus and 4000 L3 of T. colubriformis. The animals were allocated into seven groups with six animals each that received one of the following treatments: Group 1—control, no treatment; Group 2—moxidectin (0.2mg/kg body weight (BW)); Group 3—closantel (10mg/kg BW); Group 4—trichlorfon (100mg/kg BW); Group 5—levamisole phosphate (4.7mg/kg BW); Group 6—albendazole (5.0mg/kg BW); and Group 7—ivermectin (0.2mg/kg BW). Nematode fecal egg counts (FEC) were carried out on the day of treatment and again at 3, 7, 10 and 14days post-treatment. On the same occasions, composite fecal cultures were prepared for each group for production of L3, which were identified into genus. The animals were sacrificed for worm counts at 14days after treatment. The efficacy of each treatment was calculated from the arithmetic mean of the FEC or worm burden of the treated group, compared with the values of the control group. Only trichlorfon and moxidectin treatments resulted in a significant reduction of H. contortus recorded at necropsy (73% and 45% respectively). Moxidectin reduced T. colubriformis worm burdens by 82% and albendazole by 19%. All other anthelmintics resulted in no significant reduction in the numbers of worms found at necropsy. In conclusion, the isolates of H. contortus and T. colubriformis showed multiple resistance to all groups of anthelmintics tested. This is the first report, based on the controlled efficacy test, to show resistance of T. colubriformis to macrocyclic lactones in Brazil.
Journal: Parasitology International - PARASITOL INT , vol. 59, no. 4, pp. 622-625, 2010
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    • ...Severe clinical cases of nematode gastroenteric infection due to anthelmintic resistance have been reported in sheep grazing on pastures in the warm or temperate areas of Latin America (Almeida et al. 2010; da Cruz et al. 2010; Eddi et al. 1996; Cezar et al. 2010; Romero et al. 1998; Romero and Boero 2001)...
    • ...Resistance to ivermectin has been previously recognised in South American sheep for Haemonchus spp. (Almeida et al. 2010; Cezar et al. 2010)...
    • ...Trichlorphon treatments have resulted in significant reduction of H. contortus numbers at necropsy conduced on sheep infected with multidrug-resistant worms (Almeida et al. 2010), which are in conformity with the present study...

    César Fielet al. The Efficacy of Trichlorphon and Naphthalophos against Multiple Anthel...

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