Resistance to macrocyclic lactone anthelmintics by Haemonchus contortus and Ostertagia circumcincta in sheep in New Zealand

AIM: To establish the efficacy of oral formulations of ivermectin and moxidectin against naturally acquired abomasal nematode infections on a North Island sheep farm. METHODS: Two controlled slaughter trials were undertaken. In the first, 30 sheep on pasture were randomly allocated on the basis of faecal egg count to 1 of 3 groups, comprising an untreated control group and 2 treatment groups. One treatment group was given a single oral dose of ivermectin and the other a single oral dose of moxidectin, both at the manufacturer's recommended dose rates of 0.2 mg/kg liveweight. Six days after treatment, all animals were slaughtered and their abomasa recovered for worm counting. The second trial, which involved 47 animals, was essentially the same as the first except that, as well as involving the slaughter of 30 sheep from all 3 groups, 6 days after treatment, it also included a further 8 untreated control animals and 9 moxidectin treated animals which were slaughtered 27 days after treatment. RESULTS: At 6 days after treatment, moxidectin was highly effective against all 3 of the abomasal nematodes present. While ivermectin was similarly effective against Trichostrongylus axei 6 days after treatment, it was not effective against either Ostertagia circumcinta or Haemonchus contortus, against which average efficacies of only 63.6% and 61.6%, respectively, were recorded. At 27 days after treatment, moxidectin, was also highly effective against T. axei (97.3% reduction) but not against either H. contortus (71.4% reduction) or O. circumcinta (61.0% reduction). CONCLUSIONS: These results provide the first record of macrocyclic lactone resistance in H. contortus in sheep or in any other host in New Zealand, and the first case where such resistance has been exhibited in more than one parasite species at a time. Although the therapeutic efficacy of moxidectin was high against these resistant H. contortus and O. circumcincta strains, resistance to moxidectin was indicated by its diminished prophylactic activity against them. It is suggested that this reduction in the prophylactic activity of moxidectin is also likely to reduce its apparent current high therapeutic efficacy. CLINICAL RELEVANCE: As well as providing further evidence that it can no longer be automatically assumed that macrocylic lactone anthelmintics will be effective on sheep farms in this country, these findings also present a warning that increasingly complex parasite control options may have to be faced in the future.     

Resistance to macrocyclic lactone anthelmintics and associated risk factors on sheep farms in the lower North Island of New Zealand

AIM: To estimate the prevalence of resistance to macrocyclic lactone (ML) anthelmintics over a 3-year period on sheep farms in the Taihape area, and to determine associations between the presence of ML resistance and farm management practices. METHODS: All farmers with >1,000 lambing ewes served by one veterinary practice in the Taihape area of the central North Island of New Zealand were invited to take part in the study (n=157); respondents were selected on their willingness to participate. Resistance to ML was measured during 2004-2006, using a standard faecal egg count reduction test (FECRT) and a half dose of oral ivermectin (IVM; 0.1 mg/kg; n=84). Additional FECRTs were conducted separately on some farms, using full doses of IVM (n=47), levamisole (LEV; n=49), a benzimidazole (BZ; n=76), and a BZ/LEV combination (n=42). Resistance was defined as <95% faecal nematode egg count reduction (FECR) 7-10 days post-treatment. Larval cultures were performed on pooled faecal samples from all pre- and post-treatment groups for which any positive faecal nematode egg counts (FEC) were recorded. To ascertain whether particular management or drenching strategies were associated with the presence of resistance, a questionnaire comprising 50 questions was developed, and each farmer interviewed individually. RESULTS: Of all farmers invited, 84/157 (54%) participated in this study. Based on undifferentiated FEC, ML resistance to the half-dose IVM was evident on 46/84 (55%) participating farms. The majority of these cases (71%) involved Ostertagia (Teladorsagia) circumcincta. Resistance was also evident to full doses of IVM on 22/47 (47%), BZ on 41/76 (54%), LEV on 18/49 (37%), and BZ/LEV on 2/42 (5%) farms. Positive associations (p<0.05) were evident between the presence of ML resistance and management practices, such as: weaning over half of the lambs onto paddocks not grazed by lambing ewes since June; not always returning lambs to the same paddock after drenching; and the use of visual signs to assess 'worminess'. Measuring drench efficacy in January to March rather than later in the year, and presence of resistance to BZ or LEV were associated with a higher apparent prevalence of ML resistance (p<0.05). CONCLUSIONS: Anthelmintic resistance, and particularly ML resistance, was widespread on sheep farms in the Taihape area, and mostly involved O. circumcincta. The prevalence of resistance was lower on farms on which management practices, particularly those involving lambs, maintained refugia of unselected nematodes. Further investigation is required to develop control strategies which minimise selection for resistant worms, and how these may vary with climate.     

The effectiveness of benzimidazole-levamisole combination drenches in the presence of resistance to both benzimidazole and levamisole anthelmintics in New Zealand sheep

Examination of 25 cases of multiple benzimidazole and levamisole resistance, identified in sheep by faecal egg count reduction testing at the Batchelar, Lincoln and Invermay Animal Health Laboratories, showed that benzimidazole-levamisole combinations provided effective control in eight (47%) of 17 cases in which they were tested. Overall, the use of combination drenches resulted in average improvements in faecal egg count reductions of 25.6% (p<0.01) and 23.2% (p<0.05), respectively, over those achieved by the use of benzimidazole or levamisole drenches alone. The results suggest that instances of multiple resistance in which combination drenches might be effective are unlikely to be predictable either by identification of the parasites involved, or from the levels of benzimidazole or levamisole resistance present.     

Probable multigeneric resistance to macrocyclic lactone anthelmintics in cattle in New Zealand

AIM: To establish the efficacy of topical formulations of eprinomectin and abamectin against naturally acquired abomasal and small intestinal nematode infections in cattle purchased from a North Island bull-beef property. METHODS: A controlled slaughter trial, involving eighteen 6-8-month-old mixed breed calves, was conducted in May 2002.The animals were randomly allocated on the basis of faecal egg count to one of three equal-sized groups (n=6), consisting of an untreated control group and two treatment groups. One of the treatment groups was treated with a topical formulation of eprinomectin, the other with abamectin. Both anthelmintics were administered as a single topical treatment on an individual liveweight basis, at the manufacturer's recommended dose rates of 0.5 mg/kg. All calves were housed in separate groups with no access to pasture throughout the entire trial and were slaughtered 7-10 days after treatment. RESULTS: Both anthelmintic treatments were highly effective(worm count reduction >98%) against Ostertagia ostertagi, Trichostrongylus axei and Cooperia punctata, but were not effective at reducing worm counts significantly of either Cooperia oncophora or Trichostrongylus longispicularis. Against these latter two parasites, worm count reductions of only 72% and 79%, and 81% and 76%, respectively, were recorded following treatment with eprinomectin or abamectin, respectively (all p>0.05). CONCLUSIONS: These results demonstrate evidence of resistance to macrocyclic lactone anthelmintics by C. oncophora and probably T. longispicularis also. CLINICAL RELEVANCE: As well as perhaps providing the first record of resistance to any anthelmintic by T. longispicularis, the present findings may also represent the first case of resistance to macrocyclic lactone anthelmintics exhibited by more than one parasite species at a time in cattle in New Zealand. KEYWORDS: Eprinomectin, abamectin, macrocyclic lactone, anthelmintic resistance, cattle, Cooperia, Trichostrongylus.     

Multigeneric resistance to benzimidazole anthelmintics in sheep

Benzimidazole resistance involving several gastrointestinal nematode genera on a single sheep farm in New Zealand is reported for the first time. A controlled slaughter trial showed that at the recommended dose rate of 12.5 mg/kg, mebendazole had efficacies of 0, 60, 66, 90, 54 and 38% against Haemonchus contortus, Ostertagia spp., Nematodirus spp., intestinal Trichostrongylus spp., Strongyloides spp. and Oesophagostomum venulosum, respectively. The relevance of such multigeneric resistance to possible future options for controlling anthelmintic resistant sheep trichostrongylids is briefly discussed.     

新西兰梨育种系统介绍

文章基于本人在新西兰植物与食品研究院（PFR）莫图依卡研究中心2017年10月至2018年7月的梨系统育种培训学习。文中简要介绍了PFR的梨育种系统,包括育种目标的建立,亲本的选择,杂交,种子处理,苗圃管理,树体管理,果实采摘,果实评价及3S体系的介绍等。目的是将本人在新西兰的学习收获与广大梨育种者和兴趣爱好者进行分享,希望能对相关的育种工作有所帮助或启发。     

Multigeneric resistance to benzimidazole anthelmintics in four sheep flocks

Clinical parasitism associated with multigeneric resistance to benzimidazole anthelmintics was investigated in four sheep flocks during February and March 1989. The genera considered resistant were Haemonchus and Nematodirus spp. on all four farms and Trichostrongylus and Ostertagia spp. on three of the four farms. It is suggested that when investigating cases of suspected drench resistance, postdrenching worm counts are useful to help identify the resistant worm species present.     

Multigeneric resistance to benzimidazole anthelmintics in four sheep flocks

Clinical parasitism associated with multigeneric resistance to benzimidazole anthelmintics was investigated in four sheep flocks during February and March 1989. The genera considered resistant were Haemonchus and Nematodirus spp. on all four farms and Trichostrongylus and Ostertagia spp. on three of the four farms. It is suggested that when investigating cases of suspected drench resistance, post-drenching worm counts are useful to help identify the resistant worm species present.     

Scrapie in imported sheep in New Zealand

Extract

The disease known as Scrapie was diagnosed in New Zealand for the first time in June, 1952. Two positive cases and, one suspected case occurred in Canterbury in Suffolk sheep which were imported from England early in 1950. The disease appeared after a typiqally long incubation period and ran a characteristic course in the affected sheep. The outbreak of Scrapie in New Zealand and the drastic measures necessary to control it have placed new emphasis on the difficulty of preventing the introduction of this and other diseases which develop insidiously after a long incubation period, and for which no biological test is available. The same factors have also been responsible for the peculiar difficulties encountered by overseas workers in investigating Scrapie and in establishing clearly the facts of its etiology and transmission.     

Multifocal retinitis in New Zealand sheep dogs

Thirty-nine percent of 1,448 working sheep dogs were affected with varying degrees of multifocal retinal disease on ophthalmoscopic examination. Lesions consisted of localized areas of hyperreflexia in the tapetal fundus, often associated with hyperpigmentation. Severely affected animals had widespread hyperreflexia with retinal vascular attenuation. Only 6% of 125 New Zealand dogs raised in urban environment were similarly affected. Both eyes of 70 dogs from New Zealand were examined histologically. Forty-seven of 70 dogs had ocular inflammatory disease. Ten other dogs had noninflammatory eye disease, and 13 dogs had normal eyes. Histologically, eyes with inflammatory disease were divided into three categories: Dogs 3 years of age or less with active inflammatory disease of the retina, uvea, and vitreous. Four dogs in this group had migrating nematode larvae identified morphologically as genus Toxocara. Diffuse retinitis and retinal atrophy in conjunction with localized retinal necrosis and choroidal fibrosis. Dogs in this category were severely, clinically affected. Chronic, low-grade retinitis with variable retinal atrophy. Most dogs in this category were over 3 years of age, and many were visually functional. The existence of a definable spectrum of morphological changes associated with inflammation, suggests that Toxocara sp. ocular larva migrans may be the cause of a highly prevalent, potentially blinding syndrome of working sheep dogs in New Zealand.     

Enzootic pneumonia of sheep in New Zealand

Extract

Enzootic pneumonia of sheep is a specific condition confined to southern Otago and the Southland district and is commonly referred to as “Southland Pneumonia.” It has been recognized as a distinct clinical entity for many years in that area, heavy losses being reported in the Gore district of Southland in 1924.     

Lantana poisoning of cattle and sheep in New Zealand

The investigation of a field case of Lantana camara poisoning in cattle is reported. Toxicity was confirmed by the experimental dosing of two sheep with dried leaf powder at 6 and 12 mg/kg body weight. Marked cholestatic hepatophy and renal tubular disease resulted. This is the first reported case of toxicity due to grazing a Lantana camara variety grown in New Zealand.     

Lantana poisoning of cattle and sheep in New Zealand

The investigation of a field case of Lantana camara poisoning in cattle is reported. Toxicity was confirmed by the experimental dosing of two sheep with dried leaf powder at 6 and 12 mg/kg body weight. Marked cholestatic hepatophy and renal tubular disease resulted. This is the first reported case of toxicity due to grazing a Lantana camara variety grown in New Zealand.     

Prevalence of anthelmintic resistance on sheep farms in New Zealand

AIM: To establish the prevalence of anthelmintic resistance in parasitic nematodes on sheep farms in New Zealand.

METHODS: A cross-sectional prevalence study was conducted, using a standardised faecal nematode egg count (FEC) reduction (FECR) test (FECRT) for ivermectin, at a full (0.2 mg/kg) and half (0.1 mg/kg) dose rate, and albendazole, levamisole and albendazole-levamisole in combination, on 60 lambs (n=10 per group) on farms selected from throughout New Zealand. Farms that conformed with selection criteria were chosen at random (n=80) or with a history of suspected resistance to macrocy- clic lactone (ML) anthelmintics (n=32). Resistance to an an- thelmintic was inferred when there was <95% reduction in FEC 7-10 days after treatment. Larval cultures were performed for all control groups and for treated groups for which resistance was evident.

RESULTS: Of the farms randomly selected, 36% showed ≥95% FECR for all anthelmintics tested; resistance to ivermectin at 0.1 and 0.2 mg/kg liveweight was evident on 36% and 25% of these farms, respectively. Resistance to both ivermectin (0.2 mg/kg) and levamisole was evident on 8/80 (10%) farms, to ivermectin and albendazole on 10/80 (13%) farms, and to iver- mectin, levamisole and albendazole on 6/80 (8%) farms. The prevalence of resistance to a half dose of ivermectin tended to be more prevalent on farms with a history of suspected ML resistance (p=0.06). Resistance to albendazole was seen across all the main parasite genera, and to levamisole in Nematodirus, Ostertagia (= Teladorsagia) and Trichostrongylus species. Resistance to ivermectin was dominated by Ostertagia spp, although Cooperia, Nematodirus and Trichostrongylus species were also implicated.

CONCLUSION: Anthelmintic resistance in parasitic nema-todes of sheep is common in New Zealand. Not only was resistance to albendazole and levamisole common, but resistance to the ML, ivermectin, was at a higher prevalence than expected. Sheep farmers and advisors in New Zealand need to re-evaluate the way they manage parasites, and more research is urgently needed if the steady decline in anthelmintic susceptibility is to be halted.     

Prevalence of anthelmintic resistance on sheep farms in New Zealand

AIM: To establish the prevalence of anthelmintic resistance in parasitic nematodes on sheep farms in New Zealand. METHODS: A cross-sectional prevalence study was conducted, using a standardised faecal nematode egg count (FEC) reduction (FECR) test (FECRT) for ivermectin, at a full (0.2 mg/kg) and half (0.1 mg/kg) dose rate, and albendazole, levamisole and albendazole-levamisole in combination, on 60 lambs (n=10 per group) on farms selected from throughout New Zealand. Farms that conformed with selection criteria were chosen at random (n=80) or with a history of suspected resistance to macrocyclic lactone (ML) anthelmintics (n=32). Resistance to an anthelmintic was inferred when there was <95% reduction in FEC 7-10 days after treatment. Larval cultures were performed for all control groups and for treated groups for which resistance was evident. RESULTS: Of the farms randomly selected, 36% showed > or =95% FECR for all anthelmintics tested; resistance to ivermectin at 0.1 and 0.2 mg/kg liveweight was evident on 36% and 25% of these farms, respectively. Resistance to both ivermectin (0.2 mg/kg) and levamisole was evident on 8/80 (10%) farms, to ivermectin and albendazole on 10/80 (13%) farms, and to ivermectin, levamisole and albendazole on 6/80 (8%) farms. The prevalence of resistance to a half dose of ivermectin tended to be more prevalent on farms with a history of suspected ML resistance (p=0.06). Resistance to albendazole was seen across all the main parasite genera, and to levamisole in Nematodirus, Ostertagia (= Teladorsagia) and Trichostrongylus species. Resistance to ivermectin was dominated by Ostertagia spp, although Cooperia, Nematodirus and Trichostrongylus species were also implicated. CONCLUSION: Anthelmintic resistance in parasitic nematodes of sheep is common in New Zealand. Not only was resistance to albendazole and levamisole common, but resistance to the ML, ivermectin, was at a higher prevalence than expected. Sheep farmers and advisors in New Zealand need to re-evaluate the way they manage parasites, and more research is urgently needed if the steady decline in anthelmintic susceptibility is to be halted.     

Recent information on iodine deficiency in New Zealand sheep flocks

AIMS: To determine the value of pasture iodine, serum thyroxine (T4) and tri-iodothyronine (T3) concentrations and thyroid (g) to body weight (kg) ratios in lambs as criteria to predict and diagnose increased litter size and decreased perinatal mortality in response to iodine supplementation. METHODS: Results from ten iodine response trials in ewes using an oil-based intramuscular iodine preparation were reviewed along with results from investigations into goitre on five farms in the Manawatu. RESULTS: In two trials, litter size was increased by 14% and 21% in iodine-treated ewes. In only three of the 10 trials was there a significant reduction in perinatal mortality in iodine-treated ewes. CONCLUSIONS: Pasture iodine and serum thyroxine (T4) and tri-iodothyronine (T3) concentrations appeared to be unhelpful in predicting the occurrence of increased litter size and reduced perinatal mortality in response to iodine supplementation. New-born lambs from ewes not supplemented with iodine, that had a mean thyroid weight (g) to body weight (kg) ratio of 0.40 g/kg or greater, generally had a significant increase in perinatal mortality compared to lambs from iodine-supplemented ewes.     

Segmental axonopathy of Merino sheep in New Zealand

AIM: To investigate an axonopathy of Merino sheep that caused progressive hindlimb ataxia and slight to moderate paresis, with the purpose of understanding its pathogenesis.

METHODS: Tissues were fixed in buffered paraformaldehyde or paraformaldehyde and glutaraldehyde, processed into wax and epoxy resin, respectively, and examined by light and electron microscopy. Fresh frozen spinal cord and trigeminal nerve roots were subjected to homogenisation, centrifugation and two-dimensional electrophoresis. Selected protein spots were identified using matrix-assisted laser desorption ionisation (MALDI) mass spectrometry.

RESULTS. By light microscopy, there were large pale foamy spheroidal axonal swellings affecting peripheral as well as central axons. By electron microscopy, these were shown to contain many membrane-bound vesicles. The main abnormalities in expressed proteins involved cytoskeletal elements and myosin heavy chain, the latter interpreted as associated with the molecular motor myosin Va.

CONCLUSIONS: The disorder is the same as that described in Merinos in Australia as segmental axonopathy, and believed to have an inherited aetiology. The lesions and protein changes indicate abnormalities of the cytoskeleton, its relationship with the myelin sheath, and myosin Va molecular motor. The consequence appears to be abnormal axonal transport and inability to maintain the integrity of axons and their myelin sheaths.     

An inherited cataract in New Zealand Romney sheep

A bilateral cataract was noted to occur in sheep on a New Zealand Romney stud. Extensive breeding trials showed that this defect was inherited as an autosomal dominant. As such this form of cataract is of minimal importance to the sheep industry as control is merely by culling affected individuals.