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1.
In a recent communication (McKenna 2006), a comparison was made between four different methods for calculating results from faecal egg count reduction (FECR) tests (FECRTs). The first and most complex of these, referred to as FECRT1, involved the use of the formula: FECR = 100 x (1-[T2/T1][C1/C2]), where T1 and T2 represented the mean pre- and post-treatment faecal nematode egg counts (FECs) of a treated group, and C1 and C2 represented the mean pre- and post-treatment FECs of an untreated control group, respectively. The other three formulae consisted of more simplified versions of this procedure. In one of them (FECRT2), only post-treatment samples were considered, whereas the other two were based on comparisons between the FECs of groups of animals sampled at the time of anthelmintic treatment (pre-treatment) with those sampled several days later (post-treatment). Thus, FECRT2 was determined according to the formula: FECR = 100 x (1-[T2/C2]), while FECRT3 was calculated from FECR = 100 x (1-[T2/T1]). The fourth procedure (FECRT4) was based on a further simplification of FECRT3, where pre-treatment FECs from only one treatment group were used for comparison with all post-treatment results. This base-line pre-treatment group thus effectively functioned as an untreated control group and hence the formula for FECRT4 was FECR = 100 x (1-[T2/C1]). The study was based on an analysis of 210 previously published FECRTs performed in sheep or goats. In each case, FECRs were calculated using all four of these FECRT formulae, and their results compared. The results of these comparisons indicated that the use of any one of them was likely to result in similar estimates of anthelmintic efficacy and the detection of comparable numbers of cases of anthelmintic resistance continued.  相似文献   

2.
Three experiments defined the resistance profile of a population of Haemonchus contortus, which was shown to express multiple resistances to the benzimidazole, levamisole, macrocyclic lactone and salicylanilide anthelmintic classes when given as a registered combination. Study 1 was a faecal egg count reduction (FECR) test and the efficacies for the anthelmintics were monepantel, 100%; abamectin+levamisole+oxfendazole, 40.0%; and abamectin+levamisole+oxfendazole+naphthalophos, 100%. No larvae were recovered from the post-treatment cultures for monepantel or the 4-way treatment, and for the 3-way treatment the culture was 100% Haemonchus spp. Efficacies in Study 2 were calculated from mean post-mortem nematode burdens of H. contortus and were levamisole+oxfendazole, 3.1%; abamectin+levamisole+oxfendazole, 5.0%; ivermectin, 0.4%; moxidectin, 28.4% and closantel, 70.2%. Study 3 was also a FECR test that resulted in efficacies of 100% for monepantel and 83.0% for a formulated 4-way combination of abamectin+levamisole+albendazole+closantel. Larvae recovered from the post-treatment culture for the combination-treated sheep were all Haemonchus spp. Multi-resistant parasites such as examined in these studies are a continuing challenge to be managed by farmers and their advisors. Control programs must be planned and well-managed, and should include on-farm testing for anthelmintic resistance, monitoring of nematode burdens (by FEC and larval culture) to determine appropriate treatment times and the management of pastures to reduce the overall parasite challenge. This should be in balance with the generation, use and maintenance of drug-susceptible nematode populations in refugia.  相似文献   

3.
This study was undertaken to establish whether anthelmintic resistance was present in nematode parasites of horses in Denmark. Sixteen horse farms were selected for faecal egg count reduction (FECR) tests to measure the efficacy of the anthelmintic used. Resistance to benzimidazole anthelmintics was found on 13 of the 16 farms, with FECR values ranging from 80.0% to -101.3%. On the remaining 3 farms FECR was 100.0%, 99.3% and 97.2%. Results of a questionnaire study on anthelmintic usage, parasite control measures and management practices showed that horses in this study were treated on average 7.1 times/year. Horse owners changed between preparations of drugs but almost only within the same class of anthelmintics. Nine owners gave an anthelmintic treatment to purchased horses before they were introduced on the farm. On 14 farms, the same paddock was grazed every year and the average stocking rate was estimated to be 2.4 horses/ha. Strategies to avoid development of anthelmintic resistance are discussed and recommendations of parasite control on horse farms are presented.  相似文献   

4.
This study was undertaken to elucidate the presence of anthelmintic resistance in nematode parasites of sheep in Denmark. Twenty two flocks of sheep were selected for Faecal Egg Count Reduction (FECR) tests, based on a prior history of either the same anthelmintic, or anthelmintic class having been used 3 times or more over the previous 5 years. Evidence of anthelmintic resistance was detected in 7 flocks. Two flocks showed FECR of 88% and 94% after treatment with thiabendazole, FECR of another 2 were 90% and 94% following treatment with fenbendazole. Three flocks showed FECR of 73%, 89% and 94%, respectively following the use of levamisole. Ostertagia circumcincta was isolated from 1 of the latter flocks and subjected to an in vivo controlled slaughter assay. Following treatment with levamisole at the recommended dose rate of 7.5 mg/kg, FECR was 44.5% and worm counts were reduced by 67.7%. These results were further substantiated by an in vitro egg hatch paralysis assay and by measuring pepsinogen levels in treated and non-treated lambs. This is the first instance of anthelmintic resistance in sheep nematodes in Scandinavia.  相似文献   

5.
The present study included 19 stud farms, including 243 horses, that were investigated for the occurrence of anthelmintic resistant cyathostomes. The number of horses on the farms varied from nine to more than 100, and horses of all ages were included. A minimum of seven horses were used for faecal egg count reduction (FECR) tests. The anthelmintics included were: fenbendazole (paste formulation), ivermectin (paste formulation) and pyrantel (powder). Resistance to benzimidazoles was detected on 14 farms, with FECR values ranging from 65.1 to 86.3%. Larval cultures after fenbendazole treatment revealed exclusively cyathostome larvae. Ivermectin was tested on eight farms and proved to be effective on all. Pyrantel was tested on two farms and FECR test indicated high efficacy (92-97%). Egg hatch assay (EHA) results showed that mean concentrations of thiabendazole that inhibited hatching in 50% of the eggs (ED(50)) in resistant populations were over 0.1 microg ml(-1). The results of our study suggest widespread resistance to fenbendazole in equine cyathostomes in Slovakia, and possible strategies to delay anthelmintic resistance are discussed briefly.  相似文献   

6.
Abstract

AIM: To examine the effect of an anthelmintic treatment to lambs, followed immediately by a shift onto pastures with differing levels of larval contamination, on the development of anthelmintic resistance, in order to support recommendations to farmers regarding drench-and-shift practices for sustainable worm control.

METHODS: Newly weaned Romney lambs (n=72) were dosed with third-stage infective larvae (L3) of two nematode parasite species, Teladorsagia (=Ostertagia) circumcincta and Trichostrongylus colubriformis, comprising benzimidazole-resistant and -susceptible isolates, calculated to yield, after treatment with albendazole, a 95% reduction in faecal nematode egg count (FEC). Once infections became patent (Day 0), lambs were randomised into nine groups of eight animals, treated with albendazole at the manufacturer's recommended dose rate, and moved to individual pastures each previously prepared to have one of three different levels of parasite larval infestation (Treatment 1 = low contamination, Treatment 2 = medium contamination, and Treatment 3 = high contamination), and grazed on those pastures before receiving a second treatment with albendazole at Day 47. Anthelmintic resistance status in each group of lambs was measured using FEC reduction (FECR) and egghatch assays (EHA) after the first anthelmintic treatment, and FECR after the second treatment.

RESULTS: Egg-hatch assays demonstrated significant differences between treatments. The concentration of anthelmintic required to kill 50% of the eggs (LC50) for Treatment 1, comprising the least contaminated pastures, was significantly higher than for Treatments 2 and 3 on Days 33 and 40. Treatment 1 also had a significantly lower FECR at the final anthelmintic treatment, and significantly lower FEC than the other two treatments from Days 26 to 47.

CONCLUSIONS: The results demonstrated that the populations of T. circumcincta and T. colubriformis in lambs treated with anthelmintic had significantly higher levels of albendazole resistance at the end of the grazing period in lambs moved onto pastures with relatively low levels of parasite contamination than those moved onto pastures with relatively higher contamination, confirming drench-and-shift onto ‘clean’ pasture as a high-risk practice for the selection for anthelmintic resistance. While this does not necessarily preclude the use of this practice it does emphasise the importance of taking appropriate remedial action to minimise the risk.  相似文献   

7.

Background

In 2013 a Technology Adoption Program for sheep farmers was established to encourage the implementation of best management practices on sheep farms in Ireland. There were 4,500 participants in this programme in 2013. As part of this programme, farmers had the option to carry out a drench test to establish the efficacy of their anthelmintic treatment.

Results

Flock faecal samples were collected before and after treatment administration and gastrointestinal nematode eggs enumerated. In total there were 1,893 participants in the task, however only 1,585 included both a pre- and post-treatment faecal sample. Of those, 1,308 provided information on the anthelmintic product that they used with 46%, 23% and 28% using a benzimidazole (BZ), levamisole (LEV) and macrocyclic lactone (ML) product respectively. The remaining farmers used a product inapplicable for inclusion in the task such as a flukicide or BZ/LEV combination product. Samples were included for analysis of drench efficacy if the pre-treatment flock egg count was ≥200 eggs per gram and the interval post-sampling was 10–14 days for BZ products, 4–7 days for LEV products and 14–18 days for ML products. These criteria reduced the number of valid tests to 369, 19.5% of all tests conducted. If the reduction post-treatment was ≥95% the treatment was considered effective. Only 51% of treatments were considered effective using this criterion. There was a significant difference in efficacy between the anthelmintic drug classes with BZ effective in only 30% of treatments, LEV effective in 52% of cases and ML effective in 76% of cases.

Conclusions

Gastrointestinal nematode anthelmintic treatments, as practiced on Irish farms, have a high failure rate. There was a significant difference between the efficacies of the anthelmintic classes with BZ the least effective and ML the most effective.  相似文献   

8.
Weight loss, stunted growth, and death caused by gastrointestinal parasites are major constraints to livestock productivity, especially in tropical and developing countries where regular use, and misuse, of anthelmintics has led to nematode resistance. Albizia anthelmintica Brong. (Fabaceae) is traditionally employed throughout East Africa to treat helminth parasitosis in livestock. Reported efficacy has varied from 90% against mixed nematodes to just 19% against Haemonchus contortus alone. The objective of this study was to assess the anthelmintic effect of A. anthelmintica against naturally occurring infections of mixed gastrointestinal parasites, and to establish an effective treatment dose, in sheep under pastoral field conditions of northern Uganda. A. anthelmintica bark was collected and prepared according to local custom and packed into gel capsules. Fifty-five young female local mixed-breed lambs were randomly assigned to six groups, including a positive control group that received levamisole (synthetic anthelmintic) and a negative control group that received no treatment. Following the World Association for the Advancement of Veterinary Parasitology (WAAVP) dose determination guidelines, the other four groups were treated with varying doses of A. anthelmintica. Statistical analyses (using generalized linear models) were performed to assess treatment effect. There was a significant treatment (group) effect on parasite egg/oocyte counts per gram (EPG) for nematodes, but not for coccidia. The most effective dose against nematodes (0.8g, 58.7mg/kg) closely approximates what is usually given by traditional healers, 0.9g/adult sheep. It provided major and significant reduction in EPG as compared to the negative control. Anthelmintic efficacy was estimated using percent faecal egg count reduction (FECR). Other than the positive control, animals in the standard dose group showed the greatest decline in shedding of nematode eggs, with an FECR of 78%. This study indicates that A. anthelmintica holds potential as part of an integrated management plan for the control of helminths in developing countries.  相似文献   

9.
AIM: To evaluate the likely reliability of laboratory case submissions in assessing the prevalence of anthelmintic resistance in sheep nematodes in New Zealand, and to examine the possible influence of two alternative faecal nematode egg count reduction (FECR) analysis methodologies on such data. METHODS: A comparison was made between the prevalence of anthelmintic resistance determined using faecal egg count reduction tests (FECRTs) conducted on randomly selected sheep farms in a national survey with those derived from similar case material submitted to a veterinary pathology laboratory on a more ad-hoc basis. A comparison was also made between two alternative FECR analysis methodologies using the latter data. One methodology involved a partially differentiated procedure in which FECRs for individual nematode genera were only undertaken in those instances where reductions in total strongylid faecal nematode egg counts (FECs) (excluding Nematodirus) of <95% were recorded. The other was a fully differentiated method where reductions in FECs for individual parasites were undertaken in all cases. RESULTS: Although there were some differences between them the results showed that there were considerable similarities between the prevalence data obtained from both the national survey and laboratory case submissions. This was particularly evident in relation to the overall pattern of involvement of the various nematode genera and the types of anthelmintic concerned. A comparison between laboratory case submission data analysed using a partially differentiated FECR methodology with that of a fully differentiated procedure, however, suggested that the use of the former practice was likely to lead to the 'true' prevalence of resistance being underestimated. CONCLUSIONS: The results of this study indicate that examination of FECRT case submissions to veterinary laboratories may offer a useful source of information regarding changes in the prevalence of anthelmintic-resistant sheep nematodes in New Zealand. They also lend support to suggestions that the recently completed national survey may have provided a conservative estimate of the prevalence of such resistance.  相似文献   

10.
AIM: To gather information on the repeatability of a faecal nematode egg count (FEC) reduction (FECR) test (FECRT), evaluating both different methods of calculating efficacy and variations within a method, in order to supply veterinarians and other advisors with sufficient information to apply some level of confidence around a diagnosis of anthelmintic resistance based on FECRT results. METHODS: Two commercial sheep farms were selected on the basis of having previously recorded FECR <95% after treatment with ivermectin (Farm 1) or albendazole (Farm 2). On each farm at least 250 lambs, managed as a single mob, were individually ear-tagged and sampled for FEC. The resulting counts were used, 3-4 days later, to sort the lambs into 24 groups of 10. First, the animals were split into three groups of 80, having high, medium or low FEC. Second, within each of these groups the 80 animals were further divided into four replicate mobs of 20 (each with the same mean count). Third, each of these replicates was further split into two groups of 10: those that would be drenched and those that would remain as untreated controls. All animals were again faecal-sampled and those in the drenched groups were dosed, using a syringe, to their individual liveweight, with ivermectin (Farm 1) or albendazole (Farm 2). Ten days after treatment all animals were individually faecal sampled again. FEC and larval cultures were undertaken for all 24 groups from both pre- and post-treatment samples. Efficacy (FECR) of the undifferentiated FECRT was calculated using three different equations, and efficacy by genus was also calculated. RESULTS: Calculated efficacies differed between equations, and the equation which did not utilise an untreated control yielded significantly lower efficacy estimates on both farms. Faecal cultures varied considerably in the proportions of parasite genera recovered. In general, this did not differ between FEC groups, except on Farm 1 where Haemonchus spp were more common and Cooperia spp less common in high-FEC samples. Estimated efficacies against individual genera varied considerably or very little, depending on the level of resistance. On both farms, differing proportions of tests against some genera passed or failed FECRTs based on a threshold pass mark of > or =95% FECR. CONCLUSION: There was considerable variability in the outcomes of FECRTs and in larval culture results. Caution is warranted in interpreting the results of FECRTs when efficacy values fall into the 90-95% range. Further, the possibility of a test returning a false-negative result is raised, indicating that even an efficacy estimated > or =95% may not guarantee the absence of resistant parasites.  相似文献   

11.
Gastrointestinal nematode (GIN) parasitism is a major constraint to production of goats in the southeastern United States. The conventional method of control used by producers in this region is frequent use of anthelmintics during the warm season. Overuse of anthelmintics has led to an increase in the incidence of anthelmintic resistance in many parts of the world, but data on prevalence of anthelmintic resistance in GIN of goats in the southeastern United States are very limited. To address this issue, anthelmintic efficacy was determined in goat herds at the Fort Valley State University, Agricultural Research Station (FVSU-ARS) and the University of Georgia, College of Veterinary Medicine (UGA-CVM) using fecal egg count reduction (FECR) tests and DrenchRite((R)) larval development assays (LDA). At FVSU-ARS, 2-year-old Spanish goat does were randomly allocated to one of nine different treatment groups (n = 10): albendazole (ABZ; 20mg/kg body weight (BW)), fenbendazole (FBZ; 20mg/kg BW), ivermectin (IVM; 0.4 mg/kg BW), doramectin (DRM; 0.4 mg/kg BW), moxidectin (MOX; 0.4 mg/kg BW), levamisole (LEV; 12 mg/kg BW), morantel tartrate (MOR; 10mg/kg BW), a combination of IVM (0.4 mg/kg BW) and ABZ (20 mg/kg BW), and untreated controls. At UGA-CVM, goats were randomly allocated to one of five different treatment groups (n = 8): ABZ (20 mg/kg BW), IVM (0.4 mg/kg BW), MOX (0.4 mg/kg BW), LEV (12 mg/kg BW), and untreated controls. All drugs in both experiments were administered orally. Anthelmintic efficacy was calculated by comparing 14-day post-treatment FEC of treated and control animals, and percent reductions were interpreted using the World Association for the Advancement of Veterinary Parasitology guidelines for resistance. For the LDA, nematode eggs were isolated from pooled fecal samples of untreated control goats in each herd and used to perform DrenchRite((R)) assays. In the FVSU-ARS herd, MOX, LEV, the combination of IVM and ABZ, IVM, DRM, ABZ, MOR, and FBZ reduced FEC by 100, 91, 88, 78, 76, 62, 48, and 10%, respectively. In the UGA-CVM herd, MOX, LEV, ABZ and IVM, reduced FEC by 100, 94, 87, and 0%, respectively. In both herds moxidectin was the only drug tested that was fully effective. Results of the LDA were in agreement with results of the FECR tests for both herds. These data demonstrate the presence of GINs resistant to all three major anthelmintic classes in both goat herds.  相似文献   

12.

Extract

In a recent communication (McKenna2006 McKenna, PB. 2006. A comparison of faecal egg count reduction test procedures. New Zealand Veterinary Journal, 54: 202–3. [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]), a comparison was made between four different methods for calculating results from faecal egg count reduction (FECR) tests (FECRTs). The first and most complex of these, referred to as FECRT1, involved the use of the formula: FECR = 100 × (1?[T2/T1][C1/C2]), where T1 and T2 represented the mean pre- and post-treatment faecal nematode egg counts (FECs) of a treated group, and C1 and C2 represented the mean pre- and post-treatment FECs of an untreated control group, respectively. The other three formulae consisted of more simplified versions of this procedure. In one of them (FECRT2), only post-treatment samples were considered, whereas the other two were based on comparisons between the FECs of groups of animals sampled at the time of anthelmintic treatment (pre-treatment) with those sampled several days later (post-treatment). Thus, FECRT2 was determined according to the formula: FECR = 100 × (1?[T2/C2]), while FECRT3 was calculated from FECR = 100 × (1?[T2/T1]). The fourth procedure (FECRT4) was based on a further simplification of FECRT3 where pre-treatment FECs from only one treatment group were used for comparison with all post-treatment results. This base-line pre-treatment group thus effectively functioned as an untreated control group and hence the formula for FECRT4 was FECR = 100 × (1?[T2/C1]).  相似文献   

13.
In 2003 and 2004, on a total of 63 different German horse farms, a survey using the faecal egg count reduction (FECR) test was performed to investigate the efficacy of ivermectin (IVM, Ivomec) and pyrantel (PYR, Banminth) treatment against gastro-intestinal nematodes in a total of 767 horses. IVM treatment resulted in 100% reduction of the cyathostomin egg production 14 and 21 days post-treatment (d.p.t.) on 37 farms. On the remaining five farms, the mean faecal egg count reduction ranged between 97.7 and 99.9%. The mean cyathostomin FECR following PYR treatment ranged between 92.2 and 100% on the 25 farms tested. Therefore, based on the 90% FECR threshold suggested for detection of anthelmintic resistance in horses, neither IVM nor PYR anthelmintic resistance was detected. However, if the thresholds recommended for the detection of resistance in small ruminants were applied, on one and four farms signs of reduced IVM and PYR efficacy, respectively, were observed. In 2005, to further investigate these findings, the cyathostomin egg-reappearance period (ERP) following IVM treatment was examined on six selected farms, two of which were found to show less than 99.8% FECR in the previous survey. On these two latter farms, the ERP was less than 5 weeks, while on the other four it was at least 8 weeks. Earlier investigations described IVM cyathostomin ERP of at least 9 weeks. The efficacy of IVM to reduce Parascaris equorum egg excretion was also studied. On one farm in 2 consecutive years, IVM treatment did not lead to a significant reduction in P. equorum faecal egg counts in one and five young horses, respectively.  相似文献   

14.
AIM: To gather information on the repeatability of a faecal nematode egg count (FEC) reduction (FECR) test (FECRT), evaluating both different methods of calculating efficacy and variations within a method, in order to supply veterinarians and other advisors with sufficient information to apply some level of confidence around a diagnosis of anthelmintic resistance based on FECRT results.

METHODS: Two commercial sheep farms were selected on the basis of having previously recorded FECR <95% after treatment with ivermectin (Farm 1) or albendazole (Farm 2). On each farm at least 250 lambs, managed as a single mob, were individually ear-tagged and sampled for FEC. The resulting counts were used, 3—4 days later, to sort the lambs into 24 groups of 10. First, the animals were split into three groups of 80, having high, medium or low FEC. Second, within each of these groups the 80 animals were further divided into four replicate mobs of 20 (each with the same mean count). Third, each of these replicates was further split into two groups of 10: those that would be drenched and those that would remain as untreated controls. All animals were again faecal-sampled and those in the drenched groups were dosed, using a syringe, to their individual liveweight, with ivermectin (Farm 1) or albendazole (Farm 2). Ten days after treatment all animals were individually faecal- sampled again. FEC and larval cultures were undertaken for all 24 groups from both pre- and post-treatment samples. Ef- ficacy (FECR) of the undifferentiated FECRT was calculated using three different equations, and efficacy by genus was also calculated.

RESULTS: Calculated efficacies differed between equations, and the equation which did not utilise an untreated control yielded significantly lower efficacy estimates on both farms. Faecal cultures varied considerably in the proportions of parasite genera recovered. In general, this did not differ between FEC groups, except on Farm 1 where Haemonchus spp were more common and Cooperia spp less common in high-FEC samples. Estimated efficacies against individual genera varied considerably or very little, depending on the level of resistance. On both farms, differing proportions of tests against some genera passed or failed FECRTs based on a threshold pass mark of ≥95% FECR.

CONCLUSION: There was considerable variability in the outcomes of FECRTs and in larval culture results. Caution is warranted in interpreting the results of FECRTs when efficacy values fall into the 90—95% range. Further, the possibility of a test returning a false-negative result is raised, indicating that even an efficacy estimated ≥95% may not guarantee the absence of resistant parasites.  相似文献   

15.
Extract

In a recent communication(1), it was suggested that, without a corresponding measure of their initial abundance also, the results of post-treatment larval cultures undertaken to determine the identities of those nematode genera surviving an- thelmintic treatment during faecal egg count reduction (FECR) testing in sheep were likely to be largely meaningless. Since then, the validity of this statement has been queried by a number of veterinary practitioners who appear to assume that, in cases of anthelmintic resistance, the only nematode genera that might be expected to be represented in post-treatment larval cultures are those that are drench-resistant. That this latter assumption is unfounded, however, may be illustrated by an analysis of post-treatment larval culture results obtained from 102 ovine anthelmintic resistance cases identified by FECR testing at the Batchelar Animal Health Laboratory.  相似文献   

16.
AIMS: To test the hypotheses that when untreated adult ewes are rotationally grazed (follow behind) on pastures after lambs receiving routine anthelmintic treatments, the ewes can function as a source of unselected parasites in refugia, capable of slowing the development of anthelmintic resistance, and suppress the build-up of parasites resulting from the development of anthelmintic resistance. METHODS: Firstly, the potential of untreated adult ewes to slow the development of anthelmintic resistance, and to suppress parasite populations under differing levels of anthelmintic efficacy, was investigated using a simulation model. Secondly, a field trial with three replicates of each treatment compared two grazing systems (lambs only vs lambs followed by ewes) and two types of anthelmintic, viz albendazole (ALB), to which resistance was present (faecal nematode egg count reduction (FECR)=57-59%) and ivermectin plus levamisole (IL), to which resistance was absent (FECR=97-99%), in a factorial treatment structure. Parasite populations were monitored using faecal nematode egg counts (FEC), faecal larval cultures, pasture larval sampling, and slaughter of tracer lambs. Animal performance was measured using liveweight, dag score, body condition score, and fleece weights. RESULTS: Model simulations indicated that parasites cycling in the untreated ewes could slow the development of resistance being selected for by the anthelmintic treatments given to lambs and this could occur without a nett increase in larval numbers on pasture. Further, as worm control in the lambs declined with increasing levels of anthelmintic resistance the ewes increasingly functioned as nett removers of parasite larvae, effectively reducing parasite population size. In the field trial, untreated adult ewes contributed to pasture infestations of most parasite species, but not Nematodirus spp. Parasite species on pasture and infecting lambs changed when ewes were present, but larval populations on pasture in the autumn were no greater than when lambs grazed alone. In the presence of anthelmintic resistance, parasite populations were reduced when ewes grazed in rotation with lambs, implicating the ewes as nett removers of parasite challenge. CONCLUSIONS: Untreated adult ewes were a source of unselected genotypes, capable of slowing the development of anthelmintic resistance in most, but not all, parasite species. Further, the potential of adult ewes to remove from pasture more parasite larvae than they contribute through faecal contamination indicates a potentially useful role in suppressing parasite populations, particularly when worm control in lambs is less effective as a result of anthelmintic resistance.  相似文献   

17.
A study was conducted to investigate the persistent nematocidal activity of two avermectins against experimentally-induced infections of Ascaris suum in swine. Seventy-two nematode-free cross-bred pigs of similar bodyweight were randomly allotted to nine treatment groups of eight pigs each. Eight of the groups were treated with injectable solutions containing 300 microg of doramectin/kg (IM) or 300 microg of ivermectin/kg (SC) either 0 (same day), 7, 14, or 21 days prior to an oral challenge of 50000 embryonated A. suum eggs. The ninth group (control) was challenged in parallel without any avermectin treatment. At 41 or 42 days after challenge, pigs were euthanatized and adult and larval stages of A. suum were collected from the gastrointestinal tract of each pig and counted. Both avermectins significantly (P < 0.0002) reduced nematode counts when given on the day of challenge (0 days prior), and the efficacy was 100% and 97.5% for doramectin and ivermectin, respectively. Doramectin given 7 days prior to challenge significantly (P < 0.0001) reduced nematode counts, and the efficacy was 98.4%. For all other avermectin-treatment groups, nematode counts were not significantly reduced compared to those in control pigs. These data indicated that anthelmintic activity of ivermectin against A. suum persisted for less than 7 days and the activity of doramectin persisted for more than 7, but less than 14 days.  相似文献   

18.
High perinatal mortality, low milk yields and occasional ewe deaths were investigated in a Dorper sheep flock in Southern Germany. Parasitic gastroenteritis due to Trichostrongylus spp. associated with severe weight loss despite regular anthelmintic treatments of the flock was identified as the underlying cause. A faecal egg count reduction (FECR) test revealed zero reduction after treatment with ivermectin or albendazole, respectively, and a FECR of 57.9% following treatment with levamisole. These results indicate a lack of, or considerably reduced efficacy of substances from all three classical groups of anthelmintics and demonstrate that triple anthelmintic resistance is also present in Germany. The introduction of resistant worm populations with imported livestock, excessive use of anthelmintic drugs and under-dosing of goats have possibly led to the problem in the flock described. Veterinary advice on anthelmintic treatments and responsible parasite control programmes are therefore crucial in small ruminant flocks.  相似文献   

19.
Background: In the last decade, Parascaris spp. resistance to anthelmintics has been recorded in many countries. In Saudi Arabia, there are limited data available on Parascaris spp. resistance to anthelmintics.

Objective: To determine the current status of ivermectin, abamectin and praziquantel combined, and fenbendazole resistance to Parascaris spp. in horses in Saudi Arabia.

Methods: Three hundred and forty-one foals from eleven different farms were examined by faecal egg count (FEC). The foals were all Arab horses aged 17.2 ± 4.5 (SD) months. Ivermectin (n = 46 foals), abamectin and praziquantel combined (n = 46), and fenbendazole (n = 46) were administered on day 0 and faeces were collected on day 14. The study comprised 41 untreated foals as controls. Animals that have FEC of ≥100 eggs per gram (EPG) were used to measure anthelmintic efficacy. Parascaris spp. populations were considered susceptible when faecal egg count reduction (FECR) was ≥95% associated with a lower 95% confidence limit (LCL) >90%, suspected resistant when FECR ≤90% or LCL <90% and resistant when FECR <90% and LCL <90%.

Results: Prevalence of Parascaris spp. infection was 53% (179/341 horses). Anthelmintic resistance to Parascaris spp. were highest following fenbendazole (55% of farms and 65% of foals) and to a lower extent following ivermectin or the combination of abamectin and praziquantel which comprised 27% of farms (and 46% of foals) and 18% of farms (and 10% of foals), respectively.

Conclusion: These data indicate that anthelmintics-resistant Parascaris spp. populations are present on horse farms in Saudi Arabia.  相似文献   


20.
Resistance, especially to the anthelmintic benzimidazoles (BZ), has been reported in horse cyathostomes world-wide. Diagnosis of resistance has traditionally been made by faecal egg count reduction (FECR) trials, however, this technique has limitations. Some of the shortcomings may be resolved by refining the test or by using an in vitro test. FECR tests and the larval development assay (LDA) were performed on adult horses held on 15 different horse properties across a wide geographical area of NSW, Australia. FECR were measured before and 10-14 after days treatment with oxibendazole (OBZ), morantel (MOR) or ivermectin (IVM) at recommended dose rates. Eight properties were rejected following low pre-treatment egg counts, leaving seven in the study. On these, the majority of larvae recovered from faecal cultures were cyathostomes. Using a definition of resistance as a FECR of <90%, resistance to OBZ was present on six properties and to MOR on two properties. Resistance to IVM was not detected. An alternative method of calculating FECR based on individual horse egg counts pre- and post-treatment was developed and results from the same properties compared with the results of the LDA. For example, for the BZ, correlation coefficients of values of lethal concentration to kill 50% of population (LC50) on LDA and FECR percentages were -0.536 before and -0.704 after OBZ treatment. We conclude that the LDA has the potential to be a single visit test for detection of anthelmintic resistance in horse cyathostomes but requires further investigation and standardisation.  相似文献   

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