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1.
A survey was carried out in The Netherlands to determine the prevalence of benzimidazole resistance in sheep nematodes. It was shown that 47 per cent of the 59 investigated flocks harboured trichostrongylid populations with resistance to benzimidazoles, as demonstrated by an LD50 value of 0.12 micrograms ml-1 thiabendazole or higher in an in vitro egg hatch assay. On these farms Haemonchus contortus was found to be the dominant species. In two flocks resistant Ostertagia and, or, Trichostrongylus species populations were found. Farms with resistance were revisited to determine the anthelmintic efficacy in vivo by means of treatment and egg count. In only four of the 19 flocks which showed resistance in vitro was an efficacy of less than 95 per cent in vivo achieved. This means that there is a discrepancy between the in vivo and in vitro results. Resistance was found more frequently on pure sheep farms than on mixed farms. It is suggested that mixed farms offer more refuge for susceptible H contortus populations.  相似文献   

2.
A method of using commercially available benzimidazole anthelmintics in an egg hatch test, to record levels of resistance is described. The test shows that a side-resistance is present to all the benzimidazole anthelmintics tested against both Haemonchus contortus and Trichostrongylus colubriformis after selection with thiabendazole. Additional selection on the field resistant strain of H contortus with thiabendazole showed increased levels of resistance to all the compounds tested while similar selection of T colubriformis failed to change the level of resistance after 20 generations. The level of resistance recorded by the egg hatch test in vitro is greater than that recorded for adults in vivo for the CF strain of H contortus and T colubriformis. Problems associated with reading the test are mentioned as are the different levels for the threshold of activity.  相似文献   

3.
A survey of anthelmintic resistant nematodes was conducted in sheep and goat flocks in Greece using in vivo and in vitro tests. Faecal egg count reduction tests in Macedonia were all greater than 99% indicating very high sensitivity of the nematodes to anthelmintics. In vitro tests showed benzimidazole resistant Teladorsagia circumcincta in 17 out of 106 flocks on small islands. On the mainland there were only three cases of benzimidazole resistance out of 310 flocks and animals had recently been introduced to the flocks. Flocks on the islands are isolated and there are higher temperatures than on the more mountainous mainland, where flocks tend to intermingle. It is concluded that drought and isolation are likely to be the major factors accounting for the development of anthelmintic resistance in nematodes in the island flocks.  相似文献   

4.
A survey of the prevalence of anthelmintic resistant nematode populations was conducted on 32 sheep farms in the Slovak Republic. In vitro egg hatch test and larval development tests were used for the detection of resistance to benzimidazole anthelmintics and they were compared with in vivo faecal egg count reduction tests. There was agreement in the declaration of resistance between the faecal egg count reduction test and both in vitro tests. The presence of resistant populations was determined on two farms using egg hatch test. In both farms, the LD(50) values were higher than 0.1 microg TBZ/ml, indicating resistance. By using LD(99) values it might be possible to reveal relatively small proportion of resistant larvae in the population. The prevalence of benzimidazole resistance has not change on Slovak sheep farms during last decade.  相似文献   

5.
OBJECTIVE: To evaluate a laboratory test for closantel resistance in Haemonchus contortus. PROCEDURE: Field isolates of H contortus, known to be resistant to closantel, were tested in the assay. In addition, mixtures of closantel-susceptible and closantel-resistant laboratory reference strains were tested to develop a method of predicting the proportion of resistant worms in a sample from the field. RESULTS: The assay correctly identified as resistant all of the closantel-resistant field isolates of H contortus. It also identified one isolate with an in vivo efficacy of 98% as having emerging resistance. Testing of the mixtures of laboratory reference strains revealed that an isolate would be classified as resistant when it consists of about 25% or more resistant worms. Test samples that are not fully susceptible yet contain less than 25% resistant worms may be classified as emerging resistance. CONCLUSION: The in vitro migration assay is a sensitive method of detecting closantel resistance in H contortus.  相似文献   

6.
Methods have been described to assist in the detection of anthelmintic resistance in strongylid nematodes of ruminants, horses and pigs. Two tests are recommended, an in vivo test, the faecal egg count reduction test for use in infected animals, and an in vitro test, the egg hatch test for detection of benzimidazole resistance in nematodes that hatch shortly after embryonation. Anaerobic storage for submission of faecal samples from the field for use in the in vitro test is of value and the procedure is described. The tests should enable comparable data to be obtained in surveys in all parts of the world.  相似文献   

7.
In order to monitor and eventually control the spread of drug-resistant Haemonchus contortus, knowledge of the molecular mechanisms underlying resistance is essential. Here we phenotypically and genotypically characterize three multidrug-resistant H. contortus field isolates from Australia and South Africa. All were significantly less susceptible to thiabendazole than a sensitive reference strain in an in vitro egg-hatch assay. The sensitivity was further reduced in a surviving population after treatment of infected sheep with albendazole. The beta-tubulin genes were amplified from genomic DNA of the H. contortus isolates, cloned, and sequenced. There was a high degree of sequence variation. The known mutation phenylalanine-200 to tyrosine (F200Y) occurred in 60% of the sequences from resistant isolates, but not in the sensitive reference. Interestingly, 90% of the beta-tubulin sequences from resistant isolates lacking tyrosine-200 carried another mutation nearby, glutamate-198 to alanine (E198A). This mutation was not found in the sensitive isolate, nor in sequences from resistant isolates carrying the mutation F200Y. However, the mutation E198A is known from benomyl-resistant isolates of phytopathogenic fungi such as Monilinia fructicola. The finding that alanine-198 correlates with thiabendazole resistance in H. contortus isolates from South Africa and Australia suggests that also in nematodes, the mutation E198A plays a role in benzimidazole resistance. Alanine-198 alleles of beta-tubulin can be detected by PCR-RFLP and we suggest to include this test in future surveys of H. contortus field populations.  相似文献   

8.
Resistance of the canine hookworm Ancylostoma caninum to anthelmintic therapy with pyrantel is an emerging problem in canine veterinary practice. Detecting anthelmintic resistance in parasites of pets is problematic because traditional resistance-monitoring techniques used with livestock parasites, such as the faecal egg count reduction test, are often impractical for use in small animals. We used two field-collected isolates of A. caninum in an abbreviated critical trial to test their pyrantel resistance status. The strains showed high-level and low-level resistance, with in vivo pyrantel efficacies of 28% and 71%, respectively. We noted a distinct worm density dependence effect on faecal egg count during the critical trial; egg counts in the dogs containing the low-level resistant isolate were 41% higher 6 days after drug treatment, despite the removal of 71% of the adult worms by the drug treatment. We then assessed four candidate in vitro assays for their ability to detect pyrantel resistance in A. caninum larvae, using these two isolates. The assays included a new format termed the larval arrested morphology assay (LAMA), based on observation of the effects of pyrantel on the body shape adopted by infective stage A. caninum larvae in vitro. Our data suggests that three of these assays, the LAMA, the larval motility assay (LMA), and larval feeding inhibition assay (LFIA) show promise with regards to detection of pyrantel resistance in A. caninum, but the complexity of the LFIA would likely limit its suitability for field studies. In vivo pyrantel efficacies of 28% and 71% in the two A. caninum isolates were associated with a 17-fold shift in the in vitro IC(50) values measured using the LAMA. Further testing with isolates of varying degrees of resistance is required to determine which of these assays is suitable as a rapid in vitro laboratory test for pyrantel resistance in A. caninum. The present study also indicates that potential exists for the novel LAMA or the LMA to be of use in detecting pyrantel resistance in the human hookworms, Necator americanus and Ancylostoma duodenale.  相似文献   

9.
An in vitro egg development assay was used to test the resistance of eggs from a benzimidazole susceptible and a resistant strain of Haemonchus contortus to four benzimidazoles. Storage of eggs contained in faecal samples at 4 degrees C for four, 24 or 72 hours did not appear to impair the results from the in vitro egg development assay or alter the LD50. Storage for one week, however, proved to be lethal for the eggs. The average LD50 values for thiabendazole, albendazole, mebendazole and cambendazole were 0.06, 0.07, 0.96 and 2.47 ppm for the susceptible strain. For the resistant strain the values averaged 0.26, 0.24, 1.07 and 5.11 ppm.  相似文献   

10.
A modified version of the aphid tile-test, which is used to detect insecticide resistance in single adult aphids that are resistant or susceptible to organophosphate or carbamate insecticides, was used to compare the levels of non-specific esterases in strains of the trichostrongyle nematodes Haemonchus contortus, Ostertagia circumcincta and Trichostrongylus colubriformis which were known to be resistant or susceptible to benzimidazole (BZ) anthelmintics. This colorimetric assay has shown that there is significantly more non-specific esterase in the infective-stage larvae of BZ-resistant strains than in susceptible strains and this may prove to be of use in the detection of resistance to benzimidazole anthelmintics.  相似文献   

11.
Two in vivo drug resistance assays were developed using gerbils. Cross resistance, involving related babesicides as well as the chemically unrelated antibiotic, oxytetracycline, was demonstrated, but the suggestion that imidocarb may select for pathogenic strains of parasites was not supported. Limited tests of field strains did not detect resistance. It is suggested that an in vitro assay would be more appropriate for surveys through in vivo assays would be essential for confirmatory studies.  相似文献   

12.
Composite strains of Trichostrongylus colubriformis and Ostertagia spp consisting of 0, 1, 10, 25, 50, 75, 90, and 100% of known resistant strains were prepared and tested for benzimidazole resistance using faecal egg count reduction tests, in vitro egg hatch assays and tubulin binding assays. All tests detected resistance where the proportion of the resistant strain in the composite was 50% or more, whereas none of the tests unequivocally detected resistance below 25%. Egg count reduction tests were no less sensitive than the in vitro tests in detecting low levels of resistance but the egg hatch and tubulin binding assays provided a better quantitative estimate of moderate to high levels of resistance. Faecal egg count reduction therefore, provides a suitable means of detecting resistance in the field but tests, more sensitive to low levels of resistance are required. Results indicate that the use of post-treatment counts alone provides an adequate indication of anthelmintic efficiency.  相似文献   

13.
The in vitro emergence of resistance to enrofloxacin, erythromycin, tylosin, tiamulin, and oxytetracycline in three avian Mycoplasma species, Mycoplasma gallisepticum, Mycoplasma synoviae and Mycoplasma iowae was studied. Mutants were selected stepwise and their MICs were determined after 10 passages in subinhibitory concentrations of antibiotic. High-level resistance to erythromycin and tylosin developed within 2-6 passages in the three Mycoplasma species. Resistance to enrofloxacin developed more gradually. No resistance to tiamulin or oxytetracycline could be evidenced in M. gallisepticum or M. synoviae after 10 passages whereas, resistant mutants were obtained with M. iowae. Cross-sensitivity tests performed on mutants demonstrated that mycoplasmas made resistant to tylosin were also resistant to erythromycin, whereas mutants made resistant to erythromycin were not always resistant to tylosin. Some M. iowae tiamulin-resistant mutants were also resistant to both macrolide antibiotics. Enrofloxacin and oxytetracycline did not induce any cross-resistance to the other antibiotics tested. These results show that Mycoplasma resistance to macrolides can be quickly selected in vitro, and thus, providing that similar results could be obtained under field conditions, that development of resistance to these antibiotics in vivo might also be a relatively frequent event.  相似文献   

14.
Multiple resistance to benzimidazole, imidazothiazole and macrocyclic lactone anthelmintics is an emerging problem in the south-east of Scotland. The general management and nematode control strategies employed in four affected flocks (flocks 1-4) were investigated in an attempt to identify the risk factors which might have led to the appearance of production limiting disease associated with anthelmintic resistance. The important risk factors for multiple anthelmintic resistance could not be confirmed and it proved easier to criticise nematode control practices on theoretical grounds, than to propose practical solutions. It seems likely that different risk factors were involved in the four flocks. Lambs in flocks 1 and 2 had been treated with an anthelmintic at 3-4 weekly intervals with the aim of achieving suppressive nematode control, while sheep in flock 1 had been treated with an anthelmintic after they were moved onto clean grazing. Recently lambed ewes had been treated with moxidectin in three of the four flocks, with the aim of controlling their periparturient rise in faecal nematode egg output. All of these factors might have contributed to the emergence of multiple anthelmintic resistance, because they could have led to anthelmintic treatments at times when the nematode population in refugia was small, compared to that in the sheep. Annual rotation of the anthelmintic group was compromised by the emergence of benzimidazole resistance and did not prevent the emergence of multiple resistance in any of the flocks described, although the practice may have slowed the development of resistance. Underdosing may have selected for benzimidazole and imidazothiazole resistance in flock 2, associated with inaccurate estimation of the weights of terminal sire lambs. These investigations also highlighted problems associated with the diagnosis of anthelmintic resistance, in particular the confounding effects of the onset of host immunity to nematode parasites, the possible influence of the age of the adult nematode population, and the insensitivity of the undifferentiated faecal egg count reduction test in situations where resistance is emerging.  相似文献   

15.
This study was to investigate whether the monofrequency forced oscillation (MFO) technique could be accurately used for pulmonary function testing in calves. The airflow resistance measured by this technique was compared to the resistance measured by the classical reference method by an in vitro study, using an artificial lung model, and by an in vivo study, using 11 healthy calves. The effect of the reference impedance of this oscillation equipment was also investigated. The results show linear relationships (r2 > 0.924, P < 0.001) in the resistance ranges 0 to 0.7 kPa litre-1 s and 0 to 1.0 kPa litre-1 s with a reference impedance of 1.0 kPa litre-1 s and 2.0 kPa litre-1 s, respectively. The MFO resistance values lower and higher than 0.4 kPa litre-1 s are slightly overestimated and underestimated, respectively. It was shown that, if some technical requirements are met, the MFO technique is a simple, reproducible, fast and accurate method which allows measurement of airflow resistance even in field conditions.  相似文献   

16.
A benzimidazole-resistant strain of Ostertagia circumcinta (HFRO) was used experimentally to infect lambs. The level of resistance, measured by an egg hatch assay, was studied throughout each infection and also after treatment of the lambs with fenbendazole. The HFRO strain was highly resistant to benzimidazoles. There was day-to-day variation in the level of resistance throughout a single infection with a high level of resistance in the early part of the infection, around Day 27 post-inoculation of infective larvae, falling to a lower level later in the infection. Egg hatch assays on the 3 days immediately post-treatment with fenbendazole showed the resistance level was high then resistance fell to the pre-treament level after 7 days. Selection for benzimidazole resistance using fenbendazole treatment at the normal dose rate of 5 mg kg−1 over five passages of the HFRO strain in lambs failed to increase the resistance level. Storage of larvae over a 5-months period at 4°C, prior to infection of lambs, did not produce any alteration in the resistance Level. The possible reasons for the variations in resistance found with the HFRO strain are discussed along with the implications for sheep parasite control and further development of benzimidazole resistance.  相似文献   

17.
Current status of resistance to benzimidazole (BZ) group of anthelmintic drugs against caprine nematodes in Central India at Amanala goat farm, Jabalpur, Madhya Pradesh (M. P.), was systematically investigated using faecal egg count reduction (FECR) test and egg hatch test (EHT). Besides, allele-specific PCR (AS-PCR) was deployed to ascertain the susceptible genotype (alleles) especially of the Haemonchus contortus. Randomly selected 30 goats, irrespective of age and sex, were divided into three groups of 10 each, to serve as treated and untreated controls. It was ensured that the animals were not administered with an anthelmintic drug for the past 3 months prior to undertaking the study, and faecal egg counts were estimated. FECR test evidenced fenbendazole resistance by partial elimination (24.90%) copro-egg counts in the treated group of animals vis-à-vis controls with a lower confidence interval of ?26%. Further, EHT revealed ED-50 value of 0.335 μg of thiabendazole/ml, confirming benzimidazole resistance in the animals of that farm. AS-PCR showed that 62% of H. contortus larvae were homozygous resistant (rr), 24% heterozygous (rS) and 14% homozygous susceptible (SS). The genotypic frequencies of three genotypes (rr, rS and SS) were significantly (P < 0.01) different. The prevalence of benzimidazole resistance allele (r) was also significantly (P < 0.01) higher (74%) as compared to susceptible allele (S) (26%). The resistance to benzimidazole has been discussed while emphasizing improved managemental practices designed to reduce exposure of the goat population to parasites, minimize frequency of anthelmintic use at optimum dose and rotational use of different chemical groups of medicines with different mode of action, so as to overcome and combat the upcoming problem in the field.  相似文献   

18.
SUMMARY Following the apparent failure of levamisole to control infections of Haemonchus contortus in sheep at Lawes in south eastern Queensland, a strain of this parasite was isolated at the Animal Research Institute, Yeerongpilly. This strain was used to infect sheep at Yeerongpilly and the Merrindale Research Station, Victoria where four experiments to classify the resistance pattern of the parasite were carried out. Resistance to thiabendazole was first suspected in 1969, and these experiments confirmed that resistance to this drug was still present. They also showed that a strong degree of resistance had been developed to both levamisole and morantel tartrate. Other benzimidazole anthelmintics and also the organophosphorus compound naphthalophos were only moderately effective against the original isolate but rafoxanide, nitroxynil and phenothiazine were almost 100% effective. Other highly effective chemicals were disophenol and closantel. After passaging the strain for four generations with both levamisole and albendazole, resistance to both naphthalophos and the newer benzimidazole anthelmintics increased dramatically. This is the first report of a field strain of H. contortus exhibiting resistance to benzimidazole, non-benzimidazole and organophosphorus anthelmintics.  相似文献   

19.
Six cashmere goat herds in Scotland were surveyed to assess the prevalence of anthelmintic resistance and the species of nematode involved. Resistance was determined in vivo by a faecal egg count reduction test and in vitro using an egg hatch assay and specific faecal egg identification techniques. Benzimidazole resistance was present in five of the herds, insufficient eggs were obtained from the other herd to draw firm conclusions. Teladorsagia (Ostertagia) species predominated in four of the five herds in which resistance was detected and Haemonchus contorus was the dominant species in the other.  相似文献   

20.
Four calves were infected with a susceptible (laboratory) strain of Ostertagia ostertagi and four with a field strain suspected to be resistant to benzimidazoles. After 25 days two calves from each group were treated with 3.5 mg kg-1 fenbendazole. Egg output fell to zero in all treated calves. Treated calves did not harbour worms at slaughter 35 days after infection. Significant differences between the strains were shown for ED50 values for thiabendazole in the egg hatch assay, but not in the tubulin binding assay. It is concluded that benzimidazole resistance in the suspected strain cannot be confirmed.  相似文献   

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