Evaluation of a laboratory test to detect resistance to closantel in Haemonchus contortus

OBJECTIVE: To evaluate a laboratory test for closantel resistance in Haemonchus contortus. PROCEDURE: Field isolates of H contortus, known to be resistant to closantel, were tested in the assay. In addition, mixtures of closantel-susceptible and closantel-resistant laboratory reference strains were tested to develop a method of predicting the proportion of resistant worms in a sample from the field. RESULTS: The assay correctly identified as resistant all of the closantel-resistant field isolates of H contortus. It also identified one isolate with an in vivo efficacy of 98% as having emerging resistance. Testing of the mixtures of laboratory reference strains revealed that an isolate would be classified as resistant when it consists of about 25% or more resistant worms. Test samples that are not fully susceptible yet contain less than 25% resistant worms may be classified as emerging resistance. CONCLUSION: The in vitro migration assay is a sensitive method of detecting closantel resistance in H contortus.     

The Efficacy of Closantel and Rafoxanide Against Fenbendazole- and Levamisole-Resistant Haemonchus Contortus in Small Ruminants

Veterinary Research Communications -     

Evolution of High-level,Multiple Anthelmintic Resistance on a Sheep Farm in Malaysia

Anthelmintic resistance in nematode parasites of sheep and goats on a government farm in north Malaysia was monitored over a 3-year period (1997–2000). The faecal egg count reduction test (FECRT) was conducted on young sheep at the beginning and end of this period. Changes in management, designed to reduce the selection pressure for the development of anthelmintic resistance, were also implemented during this time. By far the most important parasite problem was Haemonchus contortus. In 1997, this nematode was found to be resistant to levamisole, with suspected resistance to closantel and moxidectin. However, when the FECRT was repeated 3 years later, its resistance status had become much more severe, with resistance to benzimidazole, levamisole and ivermectin, and suspected resistance to moxidectin. This rapid evolution to multiple anthelmintic resistance is a major concern that needs to be arrested. There is an urgent need to evaluate other control strategies that incorporate livestock management, the `smart' use of drugs and non-chemotherapeutic approaches, such as biological control agents.     

Anthelmintic Resistance in Pashmina (Cashmere) Producing Goats in India

Veterinary Research Communications -     

A Survey of Anthelmintic Resistance by Nematodes on Three Sheep and Two Goat Farms in Hisar (India)

Singh, S. and Yadav, C.L., 1997. A survey of anthelmintic resistance by nematodes on three sheep and two goat farms in Hisar (India). Veterinary Research Communications, 21 (6), 447-451     

2018年内蒙古察右后旗绵羊捻转血矛线虫流行病学调查及耐药性检测

为了解草原放牧绵羊捻转血矛线虫流行情况及目前常用驱虫药物的耐药情况,2018年3—10月,根据不同草场类型、不同养殖模式,在内蒙古乌兰察布市察右后旗贲红、白音察干、大陆号、锡林郭勒、土牧尔台5个地区选择16个牧场,每个牧场随机选择15只绵羊,共240只,进行绵羊捻转血矛线虫检测,发现绵羊捻转血矛线虫平均感染率为75%,平均感染强度为14.8×200个/g;选取6个牧场的感染率和感染强度都较大的绵羊进行驱虫试验,发现有5个牧场的绵羊捻转血矛线虫对阿苯达唑和伊维菌素产生了较强的耐药性。调查结果表明,察右后旗的绵羊捻转血矛线虫流行较为普遍,羊群感染较为严重,且对阿苯达唑、伊维菌素产生了不同程度的耐药性。结果提示,加强捻转血矛线虫的耐药性监测,研发新的驱虫药物,优化驱虫措施,防止盲目用药,同时加强饲养管理,改善圈舍和牧地环境卫生,依然是有效防控绵羊捻转血矛线虫的重要途径。     

Anthelmintic Resistance on an Organized Sheep Farm in India

Monitoring anthelmintic resistance in strongyle nematodes by the faecal egg count reduction test and a commercial larval development assay on an organized sheep farm in the semi-arid area of Rajasthan revealed the emergence of resistance to benzimidazoles and rafoxanide and a potential risk of the development of levamisole/tetramisole resistance. A benzimidazole/levamisole combination, avermectins and closantel were each found to be efficacious.     

虫卵孵化试验对某羊场羊线虫抗药性的检测

为了解家畜寄生线虫对使用较久的驱虫药丙硫咪唑的抗药性情况, 用虫卵孵化试验对江苏某羊场进行抗药性检测, 测得丙硫咪唑虫卵孵化半数抑制量ＩＤ５０ ＝ ０－０６０ ２ μｇ／ｍＬ, 约是敏感株（０－０２０ ４ μｇ／ｍＬ） 的３ 倍, 但较世界兽医寄生虫促进协会提出的线虫抗药性临界值（０－１ μｇ／ｍＬ） 小。虫卵减少试验也证实了该羊场不存在抗药性。因此该场羊寄生线虫尚无抗药性。     

Comparative Anthelmintic Activity of Strategic Sustained Low-level Administration of Albendazole in Feed Pellets Compared to Single Doses of Closantel and Tetramisole against Natural Ovine Parasitic Gastroenteritis

The strategic use of single therapeutic doses of closantel, tetramisole or sustained low-level administration of albendazole in feed pellets in controlling naturally acquired parasitic gastroenteritis in sheep was investigated on a farm in semi-arid Rajasthan, India. A total of 303 5- to 6-month-old sheep were divided into three groups. Two groups were dosed with single therapeutic doses of closantel and tetramisole and the third group was given a low-level medication with albendazole through feed pellets for 30 days. Faecal egg counts revealed significantly lower counts (p<0.001) in the group treated with closantel compared to the other two groups. The faecal egg counts in the group receiving sustained low-level albendazole rose after withdrawal of the medication but remained significantly lower than those in the group treated with tetramisole up to 7 weeks after treatment (p<0.05). On the other hand, in the group treated with tetramisole, the mean faecal egg count rose from 3 weeks after treatment and remained continuously higher than those in any other group up to 12 weeks after treatment. The closantel-treated group gained more body weight but the first six-monthly greasy fleece yield was greater in the group treated with medicated pellets. During the first 3 months of the experiment, three animals in the group treated with tetramisole died of parasitic gastroenteritis. Following sustained low-level administration of albendazole in feed pellets, the plasma disposition curve of both the sulphoxide and sulphone metabolites reached its plateau level by day 5 and remained almost constant thereafter. The comparative cost-effectiveness of the three treatment regimes during the first 3 months of treatment was best for the group treated with closantel followed by the group treated with medicated feed pellets.     

Duration of Anthelmintic Effect of Three Formulations of Ivermectin (Oral,Injectable and Pour-on) Against Multiple Anthelmintic-Resistant <Emphasis Type="Italic">Haemonchus contortus</Emphasis> in Sheep

We report the results of investigations that were conducted in a sheep flock in Uttaranchal, India where repeated failure of anthelmintic medication was noted. The study revealed that Haemonchus contortus in sheep had developed resistance to benzimidazoles (fenbendazole, mebendazole and albendazole), imidazothiazole (levamisole) and salicylanide (rafoxanide), while it was fully susceptible to avermectins (ivermectin). Further, the suppression of nematode egg output in faeces of sheep naturally infected with multiple anthelmintic-resistant H. contortus following treatment with ivermectin tablet (0.4 mg/kg body weight (bw), orally), ivermectin injection (1% w/v, 0.2 mg/kg bw, subcutaneously) and ivermectin pour-on (0.5 w/v, 0.5 mg/kg bw) was also studied over a period of 10 weeks post treatment. It was noted that ivermectin tablet after initial clearance of infection (faecal egg count reduction 100%), could not prevent establishment of new patent natural infection for even a single day, while ivermectin pour-on and injection prevented the establishment of new infection for 7 and 14 days post treatment, respectively. Maximum protection period (duration for which mean faecal egg count of sheep reaches 500 eggs per gram of faeces or more) of 68 days was recorded in sheep treated with injectable ivermectin, followed by pour-on (60 days) and oral (53 days) preparations.     

Response of Corriedale and Crioula Lanada Sheep to Artificial Primary Infection with Haemonchus Contortus

Clinical, parasitological and biochemical parameters were evaluated in Corriedale and Crioula Lanada sheep after a single experimental infection with Haemonchus contortus. Ten 4-month-old worm-free lambs, of each breed, were infected with 200 L₃ H. contortus per kg live weight and four uninfected animals of each breed were used as controls. Every week, the animals were weighed and blood and faecal samples were collected for measurement of packed cell volume (PCV), total serum protein (TSP) and albumin (ALB), and the number of eggs per gram of faeces (EPG), respectively. Twelve weeks after infection, the animals were slaughtered. The worm burden was determined and samples of the abomasal mucosa were processed for determination of the number of eosinophils, mast cells and globule leukocytes. No significant differences in PCV, TSP, ALB, parasite burden or the cell populations of the abomasal mucosa were observed between breeds, but Crioula lambs had a lower EPG count. The comparison of the infected groups with their respective controls revealed significant alterations in PCV, TSP and ALB in the Corriedale lambs and in PCV, TSP, ALB and the density of eosinophils and mast cells in the Crioula lambs.     

牛羊线虫抗药性及其PC检测技术研究进展

牛羊线虫病是严重影响牛羊生产性能和经济效益的主要寄生虫病，化学药物是目前防治本病的主要手段，近年来线虫抗药性。已经成为世界各地牛羊线虫控制中的首要问题。建立线虫抗药早期检测技术可以时了解抗药性及其产生的条件等，便于采取有效对策，本文简要阐述牛羊线虫抗药性的分布与检测，现有抗药性检测方法的缺点以及PCR检测技术的最新进展。     

捻转血矛线虫Hc38保守结构域所在基因片段的真核表达载体构建

根据捻转血矛线虫Hc38基因产物(登录号AY749124)保守结构域所在核酸序列设计1对引物,该引物包含Kozak序列、HindⅢ酶切位点、Xba Ⅰ酶切位点.以含有捻转血矛线虫Hc38基因保守结构域片段的pMD19-T为模板,经PCR扩增获得Hc38基因保守结构域片段,用HindⅢ、Xba Ⅰ双酶切该片段,回收后将此基因片段克隆至相同酶切回收后的真核表达载体pcDNA3.1(+)中,获得重组质粒pcD-NA3.1-Hc38.经酶切分析、序列测定和PCR鉴定,证实了重组质粒的正确性.     

Recovery of Infective 3Rd Stage Larvae of Haemonchus Contortus and Ostertagia Ostertagi Ry Migration in Agar Gel

A laboratory technique is described for the recovery of Haemonchus contortus and Ostertagia ostertagi infective larvae by migration in agar gel. The addition of bile increased the recovery rate of the haemonchus larvae, but had a somewhat depressive effect on the number of ostertagia larvae recovered. Similarly, storage at 4°G lowered the yield of larvae of both species, compared to freshly harvested larvae. However, the recovery rates for both species were sufficiently high to recommend the technique for isolation of the infective stages from field samples.     

捻转血矛线虫中肠超微结构

捻转血矛线虫中肠由单层上皮细胞所组成，未见明确的细胞界限，并向肠腔内伸出相互平行、排列整齐的微绒毛，长约6.5μm，微绒毛中心由纵贯微绒毛并相互平行的微丝构成；细胞核位于细胞中部，核膜清楚，体形大，形状不规则，有一较大的核仁，异染色质凝集成块状，电子致密度甚高。分散于核质中；上皮细胞中部细胞器丰富，有粗面内质网、线粒体、高尔基体及溶酶体；基部为胶原纤维样，并含有丰富的内质网。     

Reduced efficacy of ivermectin, abamectin and moxidectin against field isolates of Haemonchus contortus

OBJECTIVES: To investigate the reduced efficacy of ivermectin, abamectin and moxidectin against two field isolates of Haemonchus contortus. These isolates were identified on separate properties in the New England region of New South Wales. PROCEDURE: Reduced efficacy of macrocyclic lactone anthelmintics against two field isolates of H contortus was suspected. These isolates were obtained from sheep on separate farms and pen trials were performed to investigate the efficacy of macrocyclic lactones. The percentage efficacy was calculated for moxidectin, ivermectin and closantel against the isolate from one farm (VHR23) and for moxidectin, ivermectin and abamectin against the isolate from the second (VHR29). The persistent activity of moxidectin against both isolates was investigated. RESULTS: Ivermectin and closantel were found to have efficacies below 80% against established populations of VHR23. Moxidectin was effective against an established population of VHR23 but the persistent activity was reduced to 7 days. Moxidectin was also found to be effective against established populations of VHR29, however, ivermectin and abamectin were found to have efficacies below 80%. There was no evidence of persistent activity of moxidectin against VHR29. CONCLUSION: A reduction in efficacy of abamectin and/or ivermectin against field isolates of H. contortus was identified from two farms in the New England region of New South Wales. The persistent effect of moxidectin was reduced against both isolates.     

基于ITS序列的捻转血矛线虫系统进化分析

为分析捻转血矛线虫ITS序列的变异与虫株特性之间的关系,对捻转血矛线虫不同药物抗性虫株(苯并咪唑类药物抗性虫株、伊维菌素抗性虫株、莫西菌素抗性虫株、药物敏感虫株)、不同宿主来源虫株(长颈鹿、牛、绵羊、山羊、牦牛)和不同地理位置(中国、美国、意大利、法国、也门、马来西亚、澳大利亚)的分离株,以及毛圆科的其他线虫的ITS序列进行了分析。结果发现捻转血矛线虫与毛圆科其他线虫的ITS-2基因的相似性高,基于该基因建立的系统进化树可以很好地区分毛圆科不同属的线虫;捻转血矛线虫的抗药性特点与其ITS-1基因的变异进化关系不大;不同地理位置的捻转血矛线虫分离株的ITS-2基因变异很小;从野生动物长颈鹿体内分离的捻转血矛线虫的ITS-1基因与家养反刍动物分离株的差异较明显。研究结果表明捻转血矛线虫ITS序列在种内相对保守,不同虫株间变异较小,在毛圆科线虫的分子分类中具有一定意义。     

伊维菌素耐药及敏感捻转血矛线虫国内分离株的鉴定

为解决国内开展驱虫药耐药性相关研究中虫种资源缺乏问题,该研究采用国际通用方法开展了华北地区捻转血矛线虫耐伊维菌素虫株的分离工作,并采用传统形态学方法对其进行鉴定。对来源不同的耐伊维菌素捻转血矛线虫虫株进行分离,结果显示：华北地区分离到了4株对伊维菌素6倍耐药及1株对其敏感的捻转血矛线虫。该研究将为国内开展捻转血矛线虫耐伊维菌素研究及新型驱虫药物的开发提供虫种资源。