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1.
Two strains of Ostertagia circumcincta were isolated from sheep in Great Britain; one (CVL strain) from a breeding flock maintained at the Central Veterinary Laboratory, the other (H2 strain) from a commercial flock in southern England. Their resistance to benzimidazole anthelmintics was assessed by means of in vitro egg hatch assays and slaughter trials. In vitro egg hatch assays gave calculated ED50 estimates of 0.799 micrograms thiabendazole/ml for the CVL strain and 0.794 micrograms thiabendazole/ml for the H2 strain, compared with ED50 estimates of 0.038 micrograms thiabendazole/m and 0.036 micrograms thiabendazole/ml for two known susceptible strains of O circumcincta. There was a 40.7, 28.4 and 66.9 per cent reduction in the group mean worm burdens of lambs infected with the CVL strain following treatment with thiabendazole, fenbendazole and oxfendazole, respectively, and 23.8, 0.0, 79.6, 52.7, 99.9 and 100 per cent reduction in the group mean worm burdens of lambs infected with the H2 strain following treatment with thiabendazole, fenbendazole, oxfendazole, albendazole, levamisole and ivermectin, respectively. Detailed field histories for both strains are given. 相似文献
2.
The objective of the study was to investigate different aspects on the efficacy of three anthelmintics on cyathostomin nematodes
of Swedish horses. A faecal egg count reduction (FECR) test was performed on 26 farms. Horses were treated orally with recommended
doses of ivermectin, pyrantel pamoate or fenbendazole. Faecal samples were collected on the day of deworming and 7, 14 and
21 days later. No resistance was shown against ivermectin; the FECR was constantly >99%. The effect of pyrantel was assessed
as equivocal in 6 farms 14 days after treatment; the mean FECR was 99%. As many as 72% of the fenbendazole-treated groups
met the criteria for resistance; the mean FECR was 86%, ranging from 56% to 100%. A re-investigation of two farms where pyrantel
resistance had been suspected clearly revealed unsatisfactory efficacy of pyrantel on one of these farms; the FECR varied
from 72% to 89%. Twenty-six of the horses previously dosed with pyrantel or fenbendazole, and which still excreted ≥150 eggs
per gram of faeces 14 days after treatment, were dewormed with ivermectin and fenbendazole or pyrantel in order to eliminate
the remaining cyathostomins. A total of 13 cyathostomin species were identified from horses that initially received fenbendazole
and seven species were identified from pyrantel-treated individuals. The egg reappearance period (ERP) following treatment
with ivermectin and pyrantel was investigated on two farms. The shortest ERP after ivermectin treatment was 8 weeks and after
pyrantel was 5 weeks. We conclude that no substantial reversion to benzimidazole susceptibility had taken place, although
these drugs have scarcely been used (<5%) in horses for the last 10 years. Pyrantel-resistant populations of cyathostomins
are present on Swedish horse farms, but the overall efficacy of pyrantel is still acceptable. 相似文献
3.
Resistance of Teladorsagia circumcincta in goats to ivermectin In 2005, suspected ivermectin resistance of gastrointestinal nematodes was investigated in 17 goats on a farm in the Netherlands, using a faecal egg count reduction test combined with faecal larval cultures. Eight goats were treated orally with 0.2 mg/ kg ivermectin on 1 August 2005 and the other nine goats served as untreated controls. Faeces were collected from all goats on 1 August and on 12 August. Faecal egg counts were reduced by 80.6% in goats receiving ivermectin. On the basis of faecal larval cultures and the egg counts, ivermectin was found to be 100% effective against Haemonchus contortus, 15.0% effective against Teladorsagia circumcincta, and 93.3% effective against Trichostrongylus spp. The effect of levamisole and oxfendazole on gastrointestinal nematodes was also evaluated. Nine goats were treated subcutaneously with 5 mg/kg levamisole and seven goats orally with 4.5 mg/kg oxfendazole on 12 September On the basis of faecal egg counts performed on 12 and 22 September, levamisole reduced the total egg count by 95.4% and oxfendazole reduced the egg count by 85.8%. Differentiation of pooled faecal larval cultures revealed that levamisole was 99.9% effective against H. contortus, 81.9% effective against T. circumcincta, and 99.5% against Trichostrongylus spp. Oxfendazole was 75.5% effective against H. contortus, 33.2% effective against T. circumcincta, and 100% effective against Trichostrongylus spp. On 28 October the nine goats that were still present on the farm were orally treated with 0.4 mg/kg ivermectin. Faecal egg counts and differentiation of pooled larval cultures of faecal samples collected on 28 October and 9 November, respectively, revealed that total egg counts were reduced by 93.1%. Ivermectin was 49.1% effective against T. circumcincta but 100% effective against H. contortus and Trichostrongylus spp. Thus H. contortus appears to be resistant to oxfendazole and T. circumcinta appears to be resistant to oxfendazole and ivermectin. This is the first documented case of ivermectin resistance of a gastrointestinal nematode of small ruminants in the Netherlands. 相似文献
4.
The efficacy of ivermectin (0.08 per cent w/v oral solution) at different dose levels was evaluated against induced infections of adult Haemonchus contortus (21 days old) and Trichostrongylus colubriformis (21 days old) and fourth stage larvae of Oesophagostomum columbianum (17 days old), Ostertagia circumcincta (five days old) and Strongyloides papillosus (five days old). Twenty-five Boergoats (mutton goats) were randomly allocated by bodyweight within each sex to an untreated control group and four ivermectin treatment groups; ivermectin was administered at either 25, 50, 100 or 200 micrograms/kg orally, once. The goats were killed and processed for worm recovery 25 to 27 days after treatment. At 25 micrograms/kg the efficacy of ivermectin varied from 43 per cent for adult T colubriformis to more than 99 per cent for fourth larval stage O columbianum. Ivermectin at 50 micrograms/kg or higher was 99 per cent or more effective against all induced parasite infections with the exception of ivermectin at 50 micrograms/kg against S papillosus (97 per cent). For all parasites there was a statistically significant (P less than 0.05) difference between the control group and the pooled treated groups. No adverse reactions to ivermectin treatment were observed in the goats. 相似文献
5.
Anthelmintic resistance was monitored over a 30 month period within a goat herd in eastern Virginia, USA. Resistance to ivermectin, levamisole and benzimidazole drugs was detected in Haemonchus contortus using the fecal egg count reduction test (FECRT). When levamisole use was discontinued for 1 year, susceptibility to levamisole appeared to return. Although a single treatment with fenbendazole was able to reduce fecal egg counts by only 50%, two doses administered in a 12 h interval increased efficacy to 92%, however, confidence intervals indicated that resistance was still present. When fecal egg counts were determined the following year after several treatment using this protocol, the efficacy of fenbendazole had fallen again to 57% reduction in fecal egg counts. The predominant genus present in cultured composite fecal samples was Haemonchus. Trichostrongylus, Cooperia and Teladorsagia were also present in smaller numbers. 相似文献
6.
Faecal egg counts (FECs) were made on samples from 1383 horses on 64 farms in northern Germany between August 2000 and November 2001. There were significant differences between the mean FECs in the two years; in 2000, 59.6 per cent of 369 samples were positive and in 2001, 32.6 per cent of 1014 samples were positive for strongyle eggs. The results of a FEC reduction test indicated that resistance to fenbendazole was present on all 10 farms where it had been used, including in 33 of 60 horses tested. In contrast, treatment with ivermectin resulted in the complete elimination of nematode eggs in all the 77 horses tested. The mean LD50 values of the egg hatch test for thiabendazole indicated resistance on all 20 farms investigated and in 94 of 134 samples (70 per cent). 相似文献
7.
M Gunawan N C Sangster J D Kelly D Griffin H V Whitlock 《Research in veterinary science》1979,27(1):111-115
The efficacy of two recently introduced benzimidazole anthelmintics, albendazole and fenbendazole, was determined for six-day, 10-day and adult stages of resistant strains of Haemonchus contortus and Trichostrongylus colubriformis. Albendazole, at 3.8 mg/kg reduced H contortus worm counts by 92.4, 70.8 and 67.1 per cent while fenbendazole, at 5.0 mg/kg, reduced worm burdens by 51.7, 95.5 and 93.4 per cent against six-, 10- and 25-day-old parasites respectively. For T colubriformis, the corresponding reductions with albendazole were 97.7, 95.8 and 64.9 per cent and for fenbendazole 29.0, 66.3 and 33.4 per cent. Compared with susceptible strains of H contortus and T colubriformis, for which therapeutic doses of benzimidazole anthelmintics are generally highly active against all stages of development, the present results show that these drugs do not have a uniform level of activity against all developmental stages of resistant strains. 相似文献
8.
Hoste H Lespine A Lemercier P Alvinerie M Jacquiet P Dorchies P 《The Veterinary record》2004,154(25):782-785
The efficacy of the pour-on formulation of eprinomectin, at a dose rate of 0.5 mg/kg bodyweight, was assessed in sheep against three main species of gastrointestinal nematodes and against the nasal bot fly, Oestrus ovis, and some pharmacokinetic parameters were determined for 21 days after the treatment. By comparison with untreated control sheep, infected experimentally with Haemonchus contortus, Teladorsagia circumcincta and Trichostrongylus colubriformis, eprinomectin was 100 per cent effective against the two abomasal species and 99.5 per cent effective against T. colubriformis. In ewes naturally infected with the nasal bot fly, the efficacy of the drug against O. ovis was 97.7 per cent. The mean (se) systemic area under the curve (AUC) was 56.0 (26.2) ng/day/ml and the mean residence time was 5.3 (1.0) days, but there were wide variations between individual sheep. 相似文献
9.
A field study was conducted in a sheep flock in the south east of Scotland with a history of ivermectin resistance in Teladorsagia circumcincta. The objective of the study was to compare the effects of single anthelmintic treatments in ewes before turn-out onto pasture that was contaminated with a moderate level of overwintered, ivermectin resistant, T. circumcincta infective larvae. The ewes were treated according to label directions with either a long acting injectable formulation of moxidectin (1mg/kg; affording up to 14weeks persistent action against macrocyclic lactone (ML)-susceptible T. circumcincta) or an oral formulation of moxidectin (0.2mg/kg; affording up to 5weeks persistent action against ML-susceptible T. circumcincta). The lambs were enrolled in the normal management of the farm, and received a total of three oral ivermectin treatments during the 16week study. The efficacy of both treatment strategies in controlling the periparturient rise in faecal nematode worm egg counts and subsequent pasture contamination was assessed from the faecal worm egg counts of the ewes and their lambs between lambing and weaning. Ewes that were treated with the oral formulation of moxidectin shed approximately 3.5 times more T. circumcincta eggs between lambing and weaning than ewes that were treated with the long acting formulation of moxidectin. This difference was reflected in the faecal worm egg counts of the lambs that were grazed alongside the different treatment groups of ewes. The results of the current study demonstrate persistent efficacy of the long acting formulation of moxidectin against an ivermectin resistant T. circumcincta population. The decreased pasture contamination after treatment could lead to improved lamb growth and a need for fewer anthelmintic treatments, thus potentially reducing one possible selection pressure for anthelmintic resistance. However, treatment with the long acting formulation of moxidectin would give rise to fewer susceptible nematodes being present in refugia, which could increase another possible selection pressure for anthelmintic resistance, depending on the subsequent grazing management of that pasture. The rationale for use of a persistent anthelmintic drug to control the periparturient rise in faecal ML-resistant T. circumcincta egg output of the ewes is discussed and potential differences in selection for macrocyclic lactone anthelmintic resistance using the different formulations of moxidectin are acknowledged. 相似文献
10.
Ricardo J. Canever Pollyana R.C. Braga Albert Boeckh Marcelly Grycajuck Daniele Bier Marcelo B. Molento 《Veterinary parasitology》2013
The increase of anthelmintic resistance in the last years in the nematode population of veterinary importance has become a major concern. The objective of the present study was to evaluate the efficacy of the main anthelmintic drugs available in the market against small strongyles of horses in Brazil. A total of 498 horses from 11 horse farms, located in the states of Paraná, São Paulo, Rio de Janeiro and Minas Gerais, in Brazil, were treated with ivermectin, moxidectin, pyrantel and fenbendazole, orally at their recommended doses. The fecal egg count reduction test (FECRT) was used to determine the product's efficacy and fecal culture was used to determine the parasite genus. Reduction on anthelmintic efficacy was found for fenbendazole in all horse farms (11/11), pyrantel in five yards (5/11) and ivermectin had low efficacy in one of the yards studied (1/11). Multidrug resistance of up to 3 drugs classes was found in one of the tested farms (1/11). Cyathostomin were the most prevalent parasite. The results showed that resistance to fenbendazole is widespread; the efficacy of pyrantel is in a critical situation. Although the macrocyclic lactones compounds still showed high efficacy on most farms, suspected resistance to macrocyclic lactones is of great concern. 相似文献
11.
The anthelmintic resistance status of two field isolates derived from farms (farm A and B) located near Edinburgh were examined using both controlled efficacy tests (CET) and faecal egg count reduction tests (FECRT). Efficacies against fenbendazole (FBZ), levamisole (LEV) and ivermectin (IVM) and, for one isolate, against combinations of these anthelmintics and moxidectin were determined in na?ve lambs, artificially infected with the isolates and treated with the compounds at the manufacturers recommended dose rates. (FBZ, 5mg/kg bodyweight (BW); LEV, 7.5mg/kg BW; IVM, 0.2mg/kg BW; Moxidectin (MOX) 0.2mg/kg BW). In both field isolates, the predominant species found pre-treatment and the only species found post-treatment was Teladorsagia circumcincta. Resistance to FBZ, LEV and IVM was confirmed in CET and FECRT on farm A and to the latter two compounds on farm B, which had a history of benzimidazole resistance and where TBZ resistance was also demonstrated using an egg hatch assay (EHA). For the farm A isolate CET efficacies against FBZ; IVM; LEV; FBZ + IVM; FBZ + LEV; FBZ, LEV + IVM and MOX were 59, 60, 88, 94,93, 92 and 98%, respectively. The CET efficacies for the farm B isolate were 51% and 72% for LEV and IVM, respectively. 相似文献
12.
Two trials involving a total of 36 Dorset horn lambs were conducted to assess the anthelmintic efficacy of ivermectin against experimental infections of benzimidazole-resistant strains of Haemonchus contortus and Ostertagia circumcincta. Two resistant strains of each of the two species were used and in each trial the lambs were allocated to three groups. One group was given 200 micrograms ivermectin/kg bodyweight orally, the second group was given 5 mg oxfendazole/kg bodyweight orally and the third group remained untreated as controls. Fourteen days after treatment the lambs were necropsied. Ivermectin was found to be more than 99 per cent to 100 per cent effective against all four benzimidazole-resistant strains, whereas oxfendazole was 78.6 per cent and 83.8 per cent effective against the H contortus strains, and 25.6 per cent and 39.8 per cent effective against the O circumcincta strains. 相似文献
13.
The efficacy of in-feed fenbendazole at a dose rate of 7.5 mg/kg bodyweight for three consecutive days was assessed in five Arabian oryx (Oryx leucoryx), six scimitar-horned oryx (Oryx dammah), 14 slender-horned gazelles (Gazella leptoceros), eight Soay sheep (Ovis aries aries soay), 13 alpine ibex (Capra ibex ibex), six red deer (Cervus elaphus hippelaphus) and 11 Nelson's elk (Cervus elaphus nelsoni) kept in five herds in a zoo. The efficacy was assessed by means of repeated faecal egg count reduction (fecr) tests and in vitro egg hatch assays. Fenbendazole was highly effective against nematodes in five of the seven species, consistently reducing egg shedding by more than 90 per cent. In the egg hatch assays of the five herds, 50 per cent inhibition of hatching (ld50) was observed at a concentration of thiabendazole below 0.1 microg/ml. In the Arabian oryx and alpine ibex the efficacy of fenbendazole was less than 90 per cent, and the ld50 in the egg hatch assays was between 0.1 and 0.2 microg/ml thiabendazole. 相似文献
14.
Thirty-nine weaned steer calves (mean weight 284 kg) were maintained under dry-lot conditions and assigned (based on fecal nematode egg count) to one of three treatment groups of 13 animals each as follows: control (no treatment), fenbendazole (5 mg kg-1), and ivermectin (0.2 mg kg-1). Fecal samples were collected 12 h before treatment, at treatment, and 12, 24, 48 and 72 h after treatment for determination of nematode eggs per gram, and (after culture) infective larvae per gram and population distribution. The effect of treatment on egg development was observed in feces collected 12 and 24 h after treatment. There was essentially no difference in efficacy, based on egg counts, of fenbendazole and ivermectin. Egg count was reduced 100% by both anthelmintics at 72 h after treatment. Viability, based on percent of eggs reaching the infective larval stage, of developing stages at 12, 24, and 48 h after fenbendazole treatment was 0.1%, 1.1%, and 0%; after ivermectin treatment the corresponding values were 23.7%, 30.1%, and 28.6%, respectively. Fenbendazole treatment resulted in little or no development of eggs and/or larvae in feces deposited 12 and 24 h after treatment, whereas development proceeded normally (compared with the control group) in ivermectin treated feces. Population distribution of infective larvae was predominantly Haemonchus and Cooperia with some Ostertagia and Oesophagostomum. 相似文献
15.
McKenna PB 《New Zealand veterinary journal》1989,37(4):146-147
The persistent anthelmintic effect of ivermectin as a topical treatment at 500 microg/kg was evaluated against induced infections of Ostertagia ostertagi, Trichostrongylus axei and Dictyocaulus vivparus in calves. The results showed a highly significant (P<0.001) anthelmintic activity for at least 14 days against O. ostertagi and T.axei (>99 per cent efficacies) and for at least 28 days (98 per cent efficacy) against D. viviparus. 相似文献
16.
Four experiments, two with sheep and two with goats, were carried out to determine the efficacy of ivermectin, fenbendazole, levamisole, closantel and some of their combinations by faecal egg count reduction tests. In the first experiment, injectable ivermectin, oral ivermectin, fenbendazole and levamisole were tested in 6-month-old lambs, and their reduction percentages were 77%, 13%, 42% and 92%, respectively. In the second experiment, with yearling sheep, the reduction percentages were 35% for injectable ivermectin, 32% for fenbendazole, 99% for levamisole, 48% for closantel, 92% for injectable ivermectin combined with fenbendazole, 99% for injectable ivermectin combined with levamisole, and 100% for fenbendazole combined with levamisole. In the study with 18-month-old goats given the same dose rates as those recommended for sheep, the reduction percentages were 73% for injectable ivermectin, 25% for fenbendazole, and 78% for levamisole. Another group of 14-month-old goats was treated with dose rates 1.5 times those recommended for sheep and the reduction percentages were 93% for levamisole, 92% for injectable ivermectin, and 97% for a combination of levamisole and ivermectin. In all experiments with sheep and goats the gastrointestinal nematode parasites identified by larval cultures were Haemonchus contortus, Trichostrongylus spp. and Oesophagostomum spp. The gastrointestinal nematodes of both sheep and goats on this farm are resistant to ivermectin and fenbendazole, whereas levamisole is still effective in sheep, but not in goats. The results are discussed in relation to the farm as a source of breeding stock to smallholder farmers and its potential to spread anthelmintic resistance. 相似文献
17.
The inhibition of Teladorsagia and other nematode genera at the early fourth-stage is a biological process that allows the parasites to survive in their host in a dormant state when prevailing conditions may otherwise kill them or prevent their progeny from surviving in the external environment. A study was conducted in Scotland to evaluate the efficacy of monepantel, an amino-acetonitrile derivative, against natural infections of inhibited fourth-stage Teladorsagia spp. larvae. At necropsy it was determined that the untreated control sheep were additionally infected with developing fourth-stage Teladorsagia spp. larvae and this is the first published evidence on the efficacy of monepantel against natural infections of this parasite and stage. The study sheep, which had grazed on naturally contaminated pastures since birth, were transferred to indoor housing after a subset of animals was examined to confirm the presence of inhibited larvae within the study population prior to the experiment. After 14 days of housing, monepantel was orally administered at 2.5 mg/kg to half of the animals. The sheep were necropsied seven days later and their parasite burdens recovered for the determination of efficacy, which was 99.7% for the inhibited stages and 99.3% for the developing fourth-stages. In conclusion, monepantel dosed orally at 2.5 mg/kg is a highly effective treatment against naturally acquired infections of inhibited and developing fourth-stage larvae of Teladorsagia spp. 相似文献
18.
Multiple resistance to benzimidazoles (fenbendazole, albendazole and mebendazole) in a strain of Haemonchus contortus in sheep was detected on a farm where fenbendazole resistance had already been identified. Following a faecal egg count reduction test, this was confirmed by both critical and controlled anthelmintic tests. Different groups of sheep infected naturally or given an experimental infection with the fenbendazole-resistant strain were treated with the recommended doses of various anthelmintics. Compared to the control group, percentage reductions in faecal egg counts of sheep treated with fenbendazole, albendazole, mebendazole, levamisole and morantel varied between 56% and 81% and worm counts between 71% and 86%. The results indicate the presence of multiple anthelmintic resistance in this strain of H. contortus on this farm. Sheep treated with ivermectin and closantel showed 100% reductions in faecal egg and worm counts, suggesting high efficacy of these drugs against the population of H. contortus on this farm. 相似文献
19.
N Anderson 《Research in veterinary science》1977,23(3):298-302
In two experiments, conducted in cattle with naturally acquired infections of Ostertagia ostertagi, comparative assessments were made of the anthelmintic efficiency of levamisole, thiabendazole and fenbendazole, each at 1.0, 1.5 and 2.0 times the recommended dose rate. Variable efficiencies of 81 and 49 per cent for levamisole, 86 and 56 per cent for thiabendazole were obtained against adult O ostertagi. Neither drug showed substantial activity against early fourth stage larvae. Efficiency of fenbendazole against adult O ostertagi was consistently high; 85 and 89 per cent in the two experiments respectively. In the first experiment in which cattle were slaughtered two to three days after treatment, only 22 per cent of inhibited early fourth stage larvae were removed whereas in the second experiment when slaughter took place 10--11 days after treatment, this efficiency was 89 per cent. There was no increased effect of increased dose rates on treatments with thiabendazole or fenbendazole. The activity of levamisole against adult worms and inhibited larvae was increased at twice the recommended dose rate. 相似文献
20.
The efficacy of fenbendazole was investigated in piglets infected artificially with Hyostrongylus rubidus and Oesophagostomum spp. After administration of 3.5 mg/kg, five-day-old stages of H rubidus were reduced by 72.5 per cent; an effect of 78.4 per cent, 96.0 per cent and 100 per cent was achieved against five-day-old, 16-day-old and 42-day-old stages, respectively, of H rubidus using a dose of 5 mg/kg. A 55 per cent effect was obtained against five-day-old stages after the administration of 3.5 mg/kg. A dose of 5 mg/kg reduced five-day-old, 16-day-old and 42-day-old stages of Oesophagotomum spp by 72.6 per cent, 44 per cent and 100 per cent respectively. 相似文献