title: Reduced efficacy of ivermectin treatments in gastrointestinal nematode infections of grazing cattle in Japan.
abstract: Fecal egg count reduction tests (FECRT) and larval migration inhibition tests (LMIT) were conducted to assess the efficacy of ivermectin (IVM) against gastrointestinal nematodes on 2 cattle farms in northern Japan in 2009 and 2010. Twelve to 20 calves on each farm were treated topically with 0.5 mg IVM/kg 2 (Farm 2) or 4 times (Farm 1) during the grazing season (May-October). On Farm 1, fecal egg count (FEC) reduction at 14 days post-treatment ranged from 16 to 87% in 2009 and from 24 to 96% in 2010, with relatively low reductions in August and October (16-53%). Conversely, IVM treatment on Farm 2 reduced FEC by 97% in September 2009. Larvae obtained from fecal cultures and identified by PCR-RFLP analysis revealed that the dominant species on both farms prior to IVM administration was Cooperia oncophora. In 2009, the FEC reduction of C. oncophora on Farm 1 decreased from 85% in May to 56% in August. In 2010, the reduction in C. oncophora in August was 28%. In the LMIT using larvae collected from the fecal cultures on Farm 1 in May and August 2009, the EC50 value of IVM in C. oncophora in August (0.892 µg/ml) was 3 times higher than that in May (0.296 µg/ml). The results of the LMIT corroborated the FECRT data, indicating the presence of IVM-resistant C. oncophora on Farm 1, at least in August. This is the first report of IVM-resistant nematodes in Japanese cattle.
authors: Department of Veterinary Parasitology, School of Veterinary Medicine, Kitasato University, Towada, Aomori 034-8628, Japan.
authors: Noboru
authors: N
authors: Kudo
authors: Toshiro
authors: T
authors: Yoshioka
authors: Yasushi
authors: Y
authors: Watanabe
authors: Yuki
authors: Y
authors: Terazono
authors: Shino
authors: S
authors: Takenouchi
authors: Takuto
authors: T
authors: Donomoto
authors: Kensuke
authors: K
authors: Nakajima
authors: Kaori
authors: K
authors: Hitosugi
authors: Ryusuke
authors: R
authors: Tsukada
authors: Hiromi
authors: H
authors: Ikadai
authors: Takashi
authors: T
authors: Oyamada
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000188:drug therapy* / Q000469:parasitology*; D004351:Drug Resistance / Q000235:genetics*; D005243:Feces / Q000469:parasitology; D041981:Gastrointestinal Tract / Q000469:parasitology*; D007559:Ivermectin / Q000494:pharmacology / Q000627:therapeutic use*; D007564:Japan; D009349:Nematode Infections / Q000188:drug therapy / Q000662:veterinary*; D010270:Parasite Egg Count / Q000662:veterinary; D016133:Polymerase Chain Reaction / Q000662:veterinary; D012150:Polymorphism, Restriction Fragment Length; D012621:Seasons; D013045:Species Specificity
chemical_list: D007559:Ivermectin