Condi G K, Soutello R G V, Amarante A F T
UNESP - Universidade Estadual Paulista, Departamento de Parasitologia, Instituto de Biociências, Caixa Postal 510, Botucatu, SP, CEP 18618-000, Brazil.
Vet Parasitol. 2009 May 12;161(3-4):213-7. doi: 10.1016/j.vetpar.2009.01.031. Epub 2009 Feb 6.
The frequent use of anthelmintics in cattle has contributed to the emergence of gastrointestinal nematode populations resistant to the drugs available in the market. This study aimed to evaluate moxidectin efficacy in a property with suspected presence of Oesophagostomum spp. resistant to such anthelmintic. The accuracy of fecal egg count reduction test (FECRT) was also assessed through comparison with the data obtained in the controlled efficacy test (worm burden determination after necropsy). Twenty worm free steers were placed together with cattle of the farm with suspected moxidectin resistance. They became naturally infected with the parasite species present in the farm, and when fecal egg counts (FEC) were higher than 200eggs/g, the animals were randomly distributed into two groups. One group (n=10) was treated with moxidectin (0.2mg/kg; Cydectin((R)), Fort Dodge) and the other was the control group (n=10). Fecal samples from each steer were collected on the treatment day and three, seven, 10 and 14 days later for FEC and fecal cultures. At 14 days after treatment, all animals were sacrificed and the gastrointestinal nematodes were recovered, identified and counted. Mean FEC reduction in the treated group (compared with control group) was of 88, 85, 88 and 92% at days three, seven, 10 and 14 after treatment, respectively. In fecal cultures, third stage larvae of Cooperia spp. and Oesophagostomum spp. were predominant. As regards the controlled efficacy test, moxidectin had 100% efficacy against the genera Haemonchus spp. and Trichostrongylus spp., and efficacy of 65.2% for Cooperia spp. (Cooperia punctata and Cooperia pectinata), 44.8% for Oesophagostomum radiatum, and 81.4% for Trichuris spp. Most of the Cooperia spp. females obtained from the control animals showed eggs inside the uterus (98.5%); conversely, only 48.2% of the females from the treated group had eggs (P<0.001). Considering the suppression in egg output following moxidectin treatment, FECRT has to be employed with caution to avoid under estimation of the anthelmintic resistance. From necropsy results, it can be concluded that C. punctata, C. pectinata, O. radiatum and Trichuris spp. showed resistance to moxidectin.
在牛群中频繁使用驱虫药导致了对市场上现有药物产生抗性的胃肠道线虫种群的出现。本研究旨在评估莫西菌素在一个疑似存在对该驱虫药耐药的食道口线虫属的养殖场中的疗效。还通过与在对照药效试验（尸检后确定虫负荷）中获得的数据进行比较，评估了粪便虫卵计数减少试验（FECRT）的准确性。将20头未感染蠕虫的公牛与该养殖场中疑似对莫西菌素有抗性的牛放在一起。它们自然感染了养殖场中存在的寄生虫种类，当粪便虫卵计数（FEC）高于200个虫卵/克时，将动物随机分为两组。一组（n = 10）用莫西菌素（0.2毫克/千克；Cydectin((R))，辉瑞动物保健公司）治疗，另一组为对照组（n = 10）。在治疗当天以及治疗后3天、7天、10天和14天，从每头公牛采集粪便样本进行FEC和粪便培养。治疗后14天，对所有动物实施安乐死，并回收、鉴定和计数胃肠道线虫。治疗组在治疗后第3天、7天、10天和14天的平均FEC减少率（与对照组相比）分别为88%、85%、88%和92%。在粪便培养物中，库珀属线虫和食道口线虫属的三期幼虫占主导。关于对照药效试验，莫西菌素对血矛线虫属和毛圆线虫属的驱虫效果为100%，对库珀属线虫（点状库珀线虫和栉状库珀线虫）的驱虫效果为65.2%，对辐射食道口线虫的驱虫效果为44.8%，对鞭虫属的驱虫效果为81.4%。从对照动物获得的大多数库珀属线虫雌虫子宫内有虫卵（98.5%）；相反，治疗组只有48.2%的雌虫有虫卵（P<0.001）。考虑到莫西菌素治疗后虫卵产量的抑制情况，必须谨慎使用FECRT，以避免低估驱虫药抗性。从尸检结果可以得出结论，点状库珀线虫、栉状库珀线虫、辐射食道口线虫和鞭虫属线虫对莫西菌素表现出抗性。
