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1.
SUMMARY A field population of Trichostrongylus colubriformis was divided into 4 lines for exposure to selection in the laboratory. The first line was selected with 50 mg/kg thiabendazole, the second with 4 mg/kg morantel tartrate, the third with 50 mg/kg thiabendazole followed by 4 mg/kg morantel tartrate and the fourth line was not selected for drug resistance. Following at least 9 generations of selection there was no difference in LD50 or LD95 between the unselected and single selected strains of worms. The strain selected by50both thiabendazole and morantel tartrate had a significantly higher LD50 against thiabendazole, morantel tartrate and levamisole than did the other three strains. The single selected strains had LD95's of 172, 21.5 and 2.3 mg/kg for thiabendazole, morantel tartrate and levamisole respectively, compared with corresponding values of 111, 17.3 and 2.4 in the unselected strain and 124, 15.5 and 3.0 in the double selected strain. The estimated efficiency of the recommended dose of each anthelmintic against the unselected field strain was:—thiabendazole (44 mg/kg) 50% efficient, morantel tartrate (8.8 mg/kg) 76% efficient and levamisole (7.0 mg/kg) 99.9% efficient.  相似文献   

2.
Observations of erratic anthelmintic activity of fenbendazole against known standardised thiabendazole-resistant strains of Haemonchus contortus and Trichostrongylus colubriformis in sheep were investigated. Fenbendazole at a dose rate of 10 mg/kg body weight was administered by oral, intra-ruminal or intra-abomasal routes, and was most effective against both resistant strains following intra-ruminal administration. In addition thiabendazole, oxibendazole, fenbendazole, parbendazole and mebendazole plus two unrelated compounds, levamisole and morantel tartrate, were used at one and a half times their suggested or recommended therapeutic dose rate against thiabendazole-resistant strains of H contortus and T colubriformis in sheep; each drug being administered by the intra-ruminal or intra-abomasal routes. Fenbendazole was more effective against both strains following intra-ruminal administration. Parbendazole was more effective against the resistant strain of T colubriformis following intra-ruminal administration. At the dose rate chosen for the other benzimidazoles used against these resistant strains, there was no difference in anthelmintic efficacy due to route of administration. Levamisole was highly effective against both resistant strains, irrespective of the route of administration. In the groups treated with morantel tartrate, the results obtained were difficult to interpret due to mortalities and a highly variable response in the surviving sheep. Fenbendazole, thiabendazole and mebendazole when used at their suggested or recommended therapeutic dose rate in sheep, were highly effective against known thiabendazole-susceptible strains of H contortus and T colubriformis following both intra-ruminal or intra-abomasal administration.  相似文献   

3.
Oxfendazole (OFZ) was chemically modified to 1-n-butyl carbamoyl OFZ (C4-OFZ) in an attempt to improve the solubility of OFZ and enable it to be administered by injection. After intramuscular injection to sheep and cattle, C4-OFZ was metabolised to OFZ which resulted in higher plasma OFZ concentrations that persisted for a considerably longer period than those observed following administration of OFZ orally. The anthelmintic efficacy of injected C4-OFZ was tested, in sheep, against strains ofTrichostrongylus colubriformis,Haemonchus contortus andOstertagia circumcincta, which were highly resistant to benzimidazoles. In all cases, the C4-OFZ treatment showed a significant improvement in efficacy over the conventional oral OFZ drench.  相似文献   

4.
The anthelmintic efficacy of 6 non-benzimidazole compounds and thiabendazole against standardised, benzimidazole resistant strains of H. contortus and T. colubriformis in sheep was determined using a controlled test. All compounds were administered intraruminally at their recommended therapeutic dose rates and 4 of the compounds were also assessed at half their recommended therapeutic dose rates. Levimisole at a dose of 6.4 mg/kg body weight, morantel at 4.4 mg/kg and 8.8 mg/kg, naphthalophos at 6.25 mg/kg and 12.5 mg/kg, rafoxanide at 7.5 mg/kg and phenothiazine at 530 mg/kg were 98% or more effective in removing adult infections of benzimidazole resistant H. contortus. Rafoxanide at 3.75 mg/kg, phenothiazine at 265 mg/kg and carbon tetrachloride at 0.05ml/kg were less effective, removing 80%, 73% and 72% respectively of the benzimidazole resistant H. contortus worm burdens. Against the benzimidazole resistant T. colubriformis levamisole at 6.4 mg/kg, and morantel at 4.4 mg/kg and 8.8 mg/kg removed 99%, 68% and 86% respectively of the adult infections. All other anthelmintics had little or no efficacy at the dose rates tested. Thiabendazole at 44 mg/kg had no significant effect against these strains of H. contortus and T. colubriformis. Several non-benzimidazole anthelmintics have shown high efficacy in this experiment and should be suitable for treating infections with benzimidazole resistant H. contortus. Of the anthelmintics tested, only levamisole and morantel show high efficacy against benzimidazole resistant T. colubriformis.  相似文献   

5.
The 22,23-dihydro derivative (ivermectin) of the major B1 components of the avermectins was evaluated, by oral and parenteral routes, for anthelmintic activity in cattle experimentally infected with 7 gastro-intestinal nematode species and lungworm. Treatment at three dosage levels was administered when the parasites were in the L4 developmental stage or when adult. The dosage expected to remove 95% of the nematodes (ED95) by each route of administration against the various developmental stages of each species of parasite was calculated by methods of linear regression to choose dose levels to be used in subsequent developmental field trials. Parenterally, efficacy against L4 stages of Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, T. colubriformis, Cooperia oncophora, C. punctata, Oesophagostomum radiatum and Dictyocaulus viviparus exceeded 99% with treatment at 0.2 mg ivermectin/kg. Parenteral treatment of the adult parasites resulted in at least 98% reduction of worm burdens, except ? 90% for T. colubriformis, with 0.2 mg/kg. Oral treatment of L4 stages of development with 0.2 mg/kg resulted in at least a 95% reduction in worm burdens of each of the 8 species of parasite. Oral treatment of the adult worms with 0.1 mg ivermectin/kg produced at least a 98% decrease in each parasite species, except for T. colubriformis (90% reduction) for which dose-response calculations suggest 95% efficacy with oral treatment at 0.2 mg/kg.  相似文献   

6.
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.  相似文献   

7.
Sheep aged 9–10 months were vaccinated with three doses of 20 000 irradiated Trichostrongylus colubriformis larvae at fortnightly intervals. This gave 97–99% protection against subsequent “impulse” challenge with 40 000 normal larvae or “sequential” challenge with 2 000 larvae/week-day for 4 weeks.The sheep were protected against both types of challenge when worms from the immunizing infections were present at the time of challenge, and when these worms were first removed by anthelmintic treatment.  相似文献   

8.
Critical and controlled anthelmintic tests were carried out using tetramisole hydrochloride per os against adult and immature gastro-entestinal nematodes of sheep. The drug was highly effective against adult Haemonchus contortus, Ostertagia spp, Trichostrongylus axei, intestinal Trichostrongylus spp, Nematodirus spp, Oesophagostomum columbi-anum and Chabertia ovina, and against 5th stage worms of the two latter species, at 10 mg/kg bodyweight and above. Efficiency against Trichuris ovis ranged from 67 to 100% at 20 mg/kg. A dose rate of 10 mg/kg was 98 to 100% effective against 14-day old H. contortus and T. axei, and against both 7-day and 14-day old intestinal Trichostrongylus spp infections, but a rate of 15 mg/kg was required for high activity against 14-day old Ostertagia spp. Seven-day old infections of H. contortus, T. axei and particularly Ostertagia spp were more resistant, and drug activity was variable at a dose rate of 15 mg/kg. Tetramisole would appear to have good activity against 7-day and 14-day old larvae of O. columbianum at 15 mg/kg in lambs in which the development of this species tended to be retarded.  相似文献   

9.
Objective Develop a computer simulation model that uses daily meteorological data and farm management practices to predict populations of Trichostrongylus colubriformis, Haemonchus contortus and Teladorsagia (Ostertagia) circumcincta and the evolution of anthelmintic resistance within a sheep flock. Use the model to explore if increased refugia, provided by leaving some adult sheep untreated, would delay development of anthelmintic resistance without compromising nematode control. Procedures Compare model predictions with field observations from a breeding flock in Armidale, NSW. Simulate the impact of leaving 1–10% of adult sheep untreated in diverse sheep‐grazing systems. Results Predicted populations of Tr. colubriformis and T. circumcincta were less than those observed in the field, attributed to nutritional stress experienced by the sheep during drought and not accounted for by the model. Observed variation in faecal egg counts explained by the model (R2) for these species was 40–50%. The H. contortus populations and R2 were both low. Leaving some sheep untreated worked best in situations where animals were already grazing or were moved onto pastures with low populations of infective larvae. In those cases, anthelmintic resistance was delayed and nematode control was maintained when 1–4% of adult stock remained untreated. Conclusions In general, the model predicted that leaving more than 4% of adults untreated did not sufficiently delay the development of anthelmintic resistance to justify the increased production risk from such a strategy. The choice of a drug rotation strategy had an equal or larger effect on nematode control, and selection for resistance, than leaving 1–10% of adults untreated.  相似文献   

10.
Radiolabelled fenbendazole (FBZ) and thiabendazole (TBZ) were administered into the rumen or abomassum of sheep previously infected with benzimidazole-susceptible or resistant Haemonchus contortus and Trichostrongylus colubriformis. Plasma radioactivity was determined for 12 hours following anthelmintic administration and at the end of this time the incorporation of radiolabel into the parasites was determined.Incorporation of radiolabel from FBZ was significantly greater in susceptible than in resistant worms. However, with TBZ there was no significant difference. There were no significant differences in the incorporation between H. contortus and T. colubriformis. Incorporation of TBZ was greater than FBZ in the worms except after ruminal administration to sheep showing clinical parasitism resulting from infection with benzimidazole- susceptible worms. TBZ was administered at five times the dose rate as FBZ, and thus a lower proportion of the administered TBZ than FBZ was incorporated.With the exception of incorporation of TBZ by resistant worms, the route of administration had a major effect on incorporation by the parasites and on plasma levels. Based on plasma levels, TBZ appeared to be rapidly absorbed from both the rumen and abomasum, whereas FBZ was less readily absorbed from the rumen with the rate of absorption being markedly greater if FBZ was administered directly into the abomasum. The findings suggest that the rumen may act as a reservoir of FBZ prolonging the period of high anthelmintic concentration in the host. This may contribute to the high efficacy of this anthelmintic.  相似文献   

11.
A controlled slaughter trial was undertaken to evaluate the efficacy of ivermectin (0.2 mg/kg) and levamisole (8 mg/kg) against a morantel-resistant field strain of Trichostrongylus colubriformis in sheep. Mean worm count reductions of greater than 99% were recorded with both anthelmintics. The apparent contradiction between the high efficacy of levamisole and the common belief that resistance to levamisole and morantel is co-inherited, is discussed.  相似文献   

12.
Monepantel is the first compound from the recently discovered amino-acetonitrile derivative (AAD) class of anthelmintics to be developed for use in sheep. Three dose determination studies were conducted in Australia and Switzerland to identify the minimum therapeutic dose of monepantel when formulated for the oral treatment of sheep to control fourth stage (L4) gastro-intestinal nematode larvae. In each study, sheep infected with the target nematodes (selected from Haemonchus contortus, Teladorsagia (Ostertagia) circumcincta, Teladorsagia trifurcata, Trichostrongylus axei, Trichostrongylus colubriformis, Trichostrongylus vitrinus, Cooperia curticei, Cooperia oncophora, Nematodirus battus, Nematodirus filicollis, Nematodirus spathiger, Chabertia ovina and Oesophagostomum venulosum) were treated with either 1.25, 2.5 or 5.0mg monepantel/kg liveweight. Following euthanasia and worm counting, efficacy was calculated against worm counts from untreated control groups. Monepantel proved highly effective at 2.5 and 5.0mg/kg, but was only moderately effective against some nematode species (L4 stage) at 1.25mg/kg. The results also confirmed that monepantel will effectively control L4 stages of nematodes resistant to at least some of the currently available broad-spectrum anthelmintic classes (macrocyclic lactone resistant strains were not included in the studies). It was concluded that 2.5mg/kg would be a suitable minimum dose rate for a commercial product. No adverse events related to treatment with monepantel were detected.  相似文献   

13.
Multiple drug resistance by nematodes, against anthelmintics has become an important economic problem in sheep farming worldwide. Here we describe the efficacy of monepantel, a developmental molecule from the recently discovered anthelmintic class, the amino-acetonitrile derivatives (AADs). Efficacy was tested against adult stage gastro-intestinal nematodes (GINs) in experimentally and naturally infected sheep at a dose of 2.5 mg/kg body weight when administered as an oral solution. Some of the isolates used in experimental infection studies were known to be resistant to the benzimidazoles or levamisole anthelmintics; strains resistant to the macrocyclic lactones were not available for these tests. Worm count-based efficacies of >98% were determined in these studies. As an exception, Oesophagostomum venulosum was only reduced by 88% in one study, albeit with a low worm burden in the untreated controls (geometric mean 15.4 worms). Similar efficacies for monepantel were also confirmed in naturally infected sheep. While the efficacy against most species was >99%, the least susceptible species was identified as Nematodirus spathiger, and although efficacy was 92.4% in one study it was generally >99%. Several animals were infected with Trichuris ovis, which was not eliminated after the treatment. Monepantel demonstrated high activity against a broad range of the important GINs of sheep, which makes this molecule an interesting candidate for use in this species, particularly in regions with problems of anthelmintic resistance. Monepantel was well tolerated by the treated sheep, with no treatment related adverse events documented.  相似文献   

14.
Abstract

AIM: To evaluate resistance to anthelmintics containing abamectin, levamisole, and oxfendazole (AB-LEV-OX), derquantal and abamectin (DEQ-AB), moxidectin, and monepantel in naturally acquired gastrointestinal nematodes present on a sheep farm.

METHODS: Faecal nematode egg count reduction tests (FECRT) were carried out on lambs that were approximately 7 months-old and infected with naturally acquired nematodes. Lambs were randomly allocated to one of five groups (n=15 per group): treatment with 2?mg/kg derquantel and 0.2?mg/kg abamectin; 0.2?mg/kg abamectin, 8?mg/kg levamisole HCl and 4.5?mg/kg oxfendazole; 2.5?mg/kg monepantel; 0.2?mg/kg moxidectin, or no treatment. Post-treatment samples were collected 12 days later. Abomasa and small intestines were collected from two slaughtered lambs from each of the DEQ-AB, AB-LEV-OX, moxidectin and control groups 15 days after treatment, for nematode counting.

RESULTS: The FECRT demonstrated that efficacy was 90.3 (95% CI=84.2–94.1)% for AB-LEV-OX, 54.5 (95% CI=28.4–71.1)% for moxidectin, 99.2 (95% CI=97.4–99.8)% for DEQ-AB and 100% for monepantel, across all genera. For Trichostrongylus spp. efficacy was 85.5% for AB-LEV-OX and 46.7% for moxidectin. Haemonchus spp. were fully susceptible to all treatments. Post-treatment nematode counts indicated that the resistant Trichostrongylus spp. were from the small intestine.

CONCLUSIONS: Anthelmintic resistance to both AB-LEV-OX and moxidectin was present in the Trichostrongylus genus on a commercial sheep farm. Monepantel and DEQ-AB were both effective against Trichostrongylus spp. based on FECRT results.

CLINICAL RELEVANCE: This finding of resistance to an AB-LEV-OX triple-combination anthelmintic in the Trichostrongylus genus in sheep in New Zealand further limits anthelmintic treatment options available, and calls into question whether this combination is suitable for use as a quarantine treatment.  相似文献   

15.
The anthelmintic efficacy of albendazole (methyl [5-(propylthio) - 1H - benzimidazole -2 -yl] carbamate) against immature and adult Fasciola hepatica and against standardised strains of benzimidazole resistant Haemonchus contortus and Trichostrongylus colubriformis was evaluated in experimentally infected sheep. A single intrarumenal treatment of dose rates of 3.8 and 7.6 mg/kg was ineffective against immature (six weeks old) F hepatica. Dose rates of 5.7 and 7.6 mg/kg reduced the number of mature (12 weeks old) F hepatica by 70 and 91 per cent respectively. Dose rates of 5.7 and 7.6 mg/kg removed 92 and 99 per cent of four-week-old, benzimidazole resistant H contortus and 89 and 99 per cent of four-week-old, benzimidazole resistant T colubriformis.  相似文献   

16.
SUMMARY The efficiency of a new benzimidazole anthelmintic, triclabendazole, was tested against cumulative infections with Fasciola hepatica aged 1 to 12 weeks in sheep and compared with that of rafoxanide. At 10 mg/kg, triclabendazole was 99% effective in eliminating both immature and adult flukes. At a lower dose rate of 5 mg/kg, triclabendazole was highly effective against adults and significantly reduced the number of early immature flukes with an 87% overall reduction of fluke burden. Rafoxanide at 7.5 mg/kg showed high efficiency against adult fluke, but its effect on immatures was not significant, and overall efficiency was 64%.  相似文献   

17.
SUMMARY Macrocyclic lactone endectocides include two chemically distinct compounds moxidectin, a milbemycin, and ivermectin, an avermectin. The significance of the chemical differences between these compounds in relation to nematode resistance remains to be established. Reported studies indicate that moxidectin at the recommended dose rate of 0.2 mg/kg controls identified strains of nematodes, isolated from sheep and goats, with demonstrated resistance to ivermectin. This reflects the significantly greater potency of moxidectin against the 3 genera of nematodes most commonly involved in anthelmintic resistance, Haemonchus, Ostertagia and Trichostrongylus. Moxidectin, in recommended strategic treatment programmes, should reduce the risk of further development of resistance to the macrocylic lactone endectocides.  相似文献   

18.
Fifty four randomly selected farms, located throughout the North Island and the Nelson region of South Island, were surveyed for anthelmintic usage and for sheep nematodes resistant to anthelmintics.

Information on anthelmintic usage was recorded on a standardized questionnaire.

Most fanners had used both benzimidazole and non- benzimidazole broad spectrum drenches on their properties in previous years.

Sheep were being drenched, on average, 7 times within their first year of life but much less frequently thereafter. Commercial interests played the dominant role in helping farmers formulate their drenching policies.

On each farm 24 numbered ewe replacement lambs were sampled for faeces at the beginning of the trial to provide material for egg counts and larval cultures. The lambs were weighed and divided into three groups of eight. One group received thiabendazole (TBZ) at 66 mg/kg, the second levamisole (LEV) at 8mg/kg while the third remained untreated as controls. All were resampled 4 to 10 days later.

On 37 farms (74%) the faecal egg count depression (FECD) following treatment with either drench was 100%. On 7 farms TBZ was less than 100% effective as gauged by FECD. Of these 6 had an FECD above 90% and one below. LEV proved to be less than 100% effective on 8 farms. Of these 5 had FECDs greater than 90% and 3 FECDs less than 90%. Only two farms had lambs with an FECD below 100% for both LEV and TBZ.

Preliminary evidence based on larval cultures suggests that those surviving the TBZ treatment were chiefly Haemonchus and those surviving LEV Trichostrongylus spp. One population of Haemonchus resistant to TBZ has been identified by the egg-hatch technique.  相似文献   

19.
Following the failure of anthelmintic treatment to control an outbreak of trichostrongylosis in sheep, multiple resistance to levamisole and oxfendazole was confirmed in field strains of Trichostrongylus colubriformis at the CSIRO Pastoral Research Laboratory, Armidale. Resistance in Trichostrongylus spp to levamisole was also confirmed on an adjoining farm. From the results of an experiment where lambs were treated at the recommended dose rate with one or both anthelmintics, it was estimated that 32% of T. colubriformis were resistant to levamisole, 19% to oxfendazole, and 12% to both drugs. Simultaneous administration of levamisole and oxfendazole resulted in an additive anthelmintic effect. Naphthalophos (36.6 to 51.2 mg/kg) was 93% efficient against the multiple resistant strain. The similar histories of anthelmintic usage at the CSIRO Pastoral Research Laboratory and on the northern tablelands of New South Wales generally, suggest that multiple anthelmintic resistance in T. colubriformis may soon emerge as a problem on the northern tablelands.  相似文献   

20.
SUMMARY Three years after the start of an experiment to assess the merits of thiabendazole (TBZ) treatment of trichostrongylid parasites in weaner sheep, field isolates of Ostertagia spp and Trichostrongylus spp were made from weaner sheep treated under one of three treatment schemes. Treatment frequencies were “nil”, “planned” (5 or 6/year) and “regular” (every 3 weeks). In addition an isolate was taken from a group of “tracer” sheep drenched with TBZ every 10 days. Resistance to TBZ was assessed using an in vitro egg hatch assay, pre- and post-treatment faecal egg counts and a controlled anthelmintic efficiency test. Pre- and post-treatment egg counts revealed the presence of TBZ-resistance in field isolates of mixed species. Egg hatch assays indicated a level of resistance for Ostertagia spp which was proportional to the frequency of TBZ treatment. The “planned”, “regular” and “tracer” strains of Ostertagia spp had resistance ratios for eggs of 4, 13 and 15 respectively when compared to the “nil” strain. In the anthelmintic efficiency assay treatment with 44 mg kg-1 and 88 mg kg-1 of TBZ removed 82 and 96% respectively of the total Ostertagia burden (adults and larvae) from the “nil” strain and 30 and 75% respectively from the “planned” strain. The same dose rates against the “regular” and “tracer” strains and additional rates of 132 or 176 mg kg-1 against the “tracer” strain failed to reduce the Ostertagia burden significantly. Intestinal Trichostrongylus spp from all isolates were fully susceptible to TBZ at 44 mg kg-1. Levamisole at 7.0 mg kg-1 was highly effective (99% reduction) against the “tracer” strain of Ostertagia.  相似文献   

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