Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA 30602, USA.
Department of Population Health, Poultry Diagnostic and Research Center, College of Veterinary Medicine and Department of Poultry Science, College of Agricultural and Environmental Sciences, University of Georgia, Athens, GA 30602, USA.
Poult Sci. 2019 Nov 1;98(11):5412-5415. doi: 10.3382/ps/pez379.
An important factor in efficient production of poultry is management of parasites. Ascaridia dissimilis is the most prevalent small intestinal nematode parasite of turkeys with up to 100% of flocks infected. High worm burdens can cause necrotic enteritis leading to high mortality in flocks. Recently, we were made aware of multiple cases where high burdens were seen at slaughter despite the administration of anthelmintics at frequent intervals, suggesting that resistance may have evolved in A. dissimilis. To address this issue, we obtained eggs of A. dissimilis from 4 commercial turkey farms and performed controlled efficacy tests to determine if fenbendazole resistance was present. Three farms had histories of frequent use of fenbendazole and worms found at slaughter, suggesting they may have resistance, and one was an organic farm where we had no additional history other than the farm had transitioned to organic production a few years earlier. For each worm isolate there were 2 treated and 2 untreated groups containing 9 birds each, with all groups being replicated in 2 separate rooms. Birds were infected with approximately 200 infective eggs, and treated groups received fenbendazole in the water (SafeGuard Aquasol, 1 mg/kg) for 5 consecutive days starting on day 24 post-infection. One week after the last treatment birds were necropsied, intestinal contents were collected and worms enumerated. Three of the four isolates demonstrated greater than 99% efficacy, indicating they were fully susceptible to fenbendazole. However, the fourth isolate demonstrated a significantly reduced efficacy of 63.89%, indicating the presence of resistance. Interestingly, this was the organic farm, whereas the 3 farms with "suspected" resistance all turned out to be fully susceptible. Given that 1 randomly acquired isolate of A. dissimilis, out of 4 tested, demonstrated resistance in this study, fenbendazole resistance may be a much larger problem on turkey farms than is currently recognized. Additional studies are needed to determine the prevalence of resistance, as well as the economic impact that resistant A. dissimilis have on turkey production.
在禽类高效生产中，寄生虫管理是一个重要因素。异刺线虫是火鸡最常见的小肠线虫寄生虫，高达 100%的鸡群受到感染。大量的寄生虫会导致坏死性肠炎，导致鸡群死亡率升高。最近，我们注意到多个病例，尽管频繁使用驱虫剂，但在屠宰时仍发现大量寄生虫，这表明异刺线虫可能已经产生了耐药性。为了解决这个问题，我们从 4 个商业火鸡养殖场获得了异刺线虫卵，并进行了控制效果测试，以确定是否存在芬苯达唑耐药性。其中 3 个养殖场有频繁使用芬苯达唑和屠宰时发现寄生虫的历史，这表明它们可能已经产生了耐药性，而另一个是有机农场，除了几年前农场已经过渡到有机生产之外，我们没有其他额外的历史。对于每个虫株，有 2 个治疗组和 2 个未处理组，每组 9 只鸟，每组在 2 个独立的房间中重复。鸟类感染了大约 200 个感染性卵，感染后第 24 天开始，治疗组连续 5 天在水中（SafeGuard Aquasol，1mg/kg）服用芬苯达唑。最后一次治疗后 1 周，剖检鸟类，收集肠道内容物并计数寄生虫。这 4 个虫株中有 3 个显示出大于 99%的疗效，表明它们对芬苯达唑完全敏感。然而，第 4 个虫株显示出 63.89%的疗效显著降低，表明存在耐药性。有趣的是，这是有机农场，而 3 个“疑似”耐药的农场最终都被证明是完全敏感的。鉴于在本研究中，随机获得的 4 个异刺线虫分离株中，有 1 个显示出耐药性，因此，芬苯达唑耐药性在火鸡养殖场可能是一个比目前认识到的更大的问题。需要进一步研究来确定耐药性的流行程度，以及耐药性异刺线虫对火鸡生产的经济影响。
