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1.
《Veterinary parasitology》2015,207(1-2):34-43
In order to investigate the incidence and distribution of adult fluke resistance to the fasciolicide tricalbendazole (TCBZ) amongst populations of Fasciola hepatica in sheep flocks in Northern Ireland (NI), individual rectal faeces samples were collected from 3 groups of 20 sheep, before (pre-dose), and 21 days after (post-dose) treatment of the animals with TCBZ, nitroxynil or closantel, on each of 13 well-managed sheep farms distributed across the province. The efficacy of each flukicide was determined for each farm, using faecal egg count reduction (FECRT) and F. hepatica coproantigen ELISA testing. In certain flocks, 2 sheep with high pre-dose faecal egg counts (FEC) were killed 3 days and 21 days respectively after TCBZ treatment, and the histology of the fluke reproductive organs was compared with that of flukes from untreated sheep, and from sheep treated with nitroxynil or closantel 2 days prior to death, using haematoxylin and eosin (H&E) staining and an in situ hybridisation method (TdT-mediated dUDP nick end labelling [TUNEL]) to demonstrate apoptosis. Results from FECRT revealed that in all flocks with a high fluke burden, TCBZ was ineffective in treating chronic fasciolosis, and this finding was generally supported by the results of the coproantigen reduction test (CRT). The histology of reproductive organs of flukes from TCBZ-treated sheep in these flocks was normal, when compared with untreated flukes, and this, together with the FECRT and CRT findings, indicated a likely diagnosis of TCBZ resistance in all the flocks with a high fluke burden. In contrast, nitroxynil and closantel were found to be fully effective against TCBZ-resistant flukes in each of the flocks bearing a high chronic fluke burden. All of the flocks with a high fluke burden and TCBZ resistance were managed on lowland in the South and East of NI. Upland flocks, in the North and West, had low fluke burdens, or were clear of infection; and FECs were too low to allow valid resistance testing. The study highlights the high level of penetration of TCBZ resistance throughout F. hepatica populations in areas of intensively managed sheep production with a high level of fluke challenge. Further, it emphasises the importance of pre-emptive chemotherapeutic action against chronic fasciolosis, using flukicides effective against the egg-producing adult flukes to minimise pasture contamination for the next season's lamb crop. This study also exemplifies the use of several complementary methods (FECRT; CRT; fluke histology; comparative anthelmintic efficacy testing) for confirmation of a diagnosis of fluke drug resistance.  相似文献   

2.
Objective   To determine the efficacy of triclabendazole (TCBZ) against 28-day-old, early immature liver fluke in cattle and its pharmacokinetics following administration by the oral or topical (pour-on) route.
Procedures   Cattle (n = 18) were infected with 500 TCBZ-susceptible liver fluke metacercariae and randomly allocated to three groups. At 28 days after infection, the groups were: (1) untreated controls; (2) treated with oral TCBZ at 12 mg/kg in combination with oxfendazole and selenium (TOS); (3) treated with pour-on TCBZ at 30 mg/kg in combination with abamectin (TA). Blood samples were taken immediately prior to treatment and serially after treatment to assess the plasma profile of TCBZ metabolites. Ten weeks after treatment all animals were slaughtered and total liver fluke counts, fluke egg counts and liver pathology were assessed.
Results   Both the TOS and TA treatments resulted in significant reductions of 28-day-old liver fluke, as assessed by fluke counts and fluke egg counts at slaughter, and the reductions following TOS treatment were significantly greater than those following TA treatment. The blood profile of TCBZ metabolites in TOS-treated animals showed a significantly greater area under the plasma concentration time curve and a higher maximum observed concentration than those treated with TA. There was significantly less liver pathology in TOS-treated animals than in the TA-treated animals.
Conclusion   TCBZ administered orally at 12 mg/kg resulted in greater efficacy against 28-day-old, early immature liver fluke than was achieved by topical administration at 30 mg/kg. Plasma metabolites of TCBZ were higher and liver pathology was less in TOS-treated animals than in TA-treated animals.  相似文献   

3.
The effect of closantel (10 mg/kg orally) and triclabendazole (10 mg/kg orally) on the reappearance of a patent infection of Fasciola hepatica was studied in experimentally infected sheep. The treatments resulted in the interruption of faecal egg output for 11 weeks with triclabendazole and 13 weeks with closantel. Necropsy of untreated control animals revealed a mean burden of 360 flukes with a mean (+/- se) surface area of 171 +/- 64.3 mm2, whereas the fluke burdens in the closantel and triclabendazole-treated animals 14 weeks after treatment were 61 (83 per cent reduction) and 21 (94 per cent reduction), respectively. The surface areas of the flukes in the triclabendazole-group were comparable with the untreated controls (141 +/- 51.8 mm2), but the flukes in the closantel group were markedly smaller (43.1 +/- 26.9 mm2). It is concluded that closantel has, in epidemiological terms, a potency comparable with that of triclabendazole, despite its slightly lower efficacy against the very immature stages.  相似文献   

4.
Efficacy of clorsulon was evaluated against infection with immature Fascioloides magna in 24 cattle and 12 sheep. Infections were induced by oral administration of 600 metacercariae/host. In cattle, clorsulon at dosages of 7 and 21 mg/kg of body weight was 65 and 100% effective against 8-week-old flukes, and 20 and 74% effective against 16-week-old flukes, respectively. In sheep, clorsulon at a dosage of 21 mg/kg was 92% effective against 8-week-old flukes. Significantly (P less than 0.05) more F magna were recovered from untreated sheep than from untreated cattle.  相似文献   

5.
Efficacy of clorsulon against the trematode Nanophyetus salmincola was evaluated in coyotes. Ten 16-week-old coyote pups were fed fish that contained metacercariae of N. salmincola. Twenty-one days later, 5 of the coyotes were given a suspension of clorsulon (approx 16 mg/kg of body weight, orally). Within 30 days after treatment, the numbers of fluke eggs in fecal specimens from the 5 treated coyotes had not decreased, and numbers of fluke eggs and flukes recovered from treated coyotes at necropsy did not differ from numbers of fluke eggs and flukes recovered from 5 untreated coyotes. Therefore, clorsulon at a dosage of 16 mg/kg was not effective against N. salmincola.  相似文献   

6.
In the winter of 2008, cattle on a farm in the province of Neuquen, Argentina died from subacute and chronic liver fluke disease despite four previous treatments with Triclabendazole (TCBZ). In the spring of 2009, a preliminary efficacy test revealed good performance using nitroxynil, whereas TCBZ efficacy was only 18% by egg counts of Fasciola eggs in the faeces. Resistance to Fasciola hepatica to TCBZ has never been reported in South America, so in January of 2010 a controlled trial was conducted to confirm and to define the degree of resistance in this herd. In a clinical trial, the fluke egg output was monitored on Days 14 and 21 and serum enzymes gamma-glutamyl transpeptidase (GGT) and glutamic-oxaloacetic transaminase (GOT) on Days 0 and 21 in 36 calves treated with TCBZ or with closantel. The results showed a reduction of 100% in fluke egg output at Days 14 and 21 for closantel. The mean epg in the TCBZ-treated groups did not decrease. Because of the fact that in this study TCBZ treatment in cattle had no effect, even at double the recommended dose, it is highly indicative that resistance of F. hepatica against TCBZ is present on this farm. The GGT and GOT levels decreased in the closantel-treated group as a result of the treatment at 21 days after dosing. To evaluate the importance of TCBZ resistance in F. hepatica in Argentina, a study on more farms from endemic areas is needed.  相似文献   

7.
In a study to evaluate the efficacy of clorsulon against Fascioloides magna infection in sheep, 12 ewes were inoculated orally with 100 metacercariae of F magna, and 6 were treated with clorsulon (15 mg/kg of body weight) 8 weeks after inoculation. The sheep were euthanatized 16 weeks after inoculation, flukes were recovered, and the liver and other tissues were subjectively scored for the severity of lesions (0 to 4+). The number of flukes recovered from the clorsulon-treated group (3.8 +/- 1.2 flukes) was significantly (P = 0.025) lower than the number of flukes recovered from the group of untreated controls (10.0 +/- 6.6 flukes). The severity of lesions was significantly (P = 0.004) reduced (45.9%) in the treated group (2.0 +/- 1.1), compared with that in the untreated controls (3.7 +/- 0.5). In the untreated group, 3 sheep died and 1 became moribund 14 to 16 weeks after inoculation. The data suggested that a single treatment with clorsulon at a dosage of 15 mg/kg 8 weeks after inoculation was not effective in preventing F magna infection in sheep, because the survival of only a few F magna is potentially fatal in sheep within 6 months after infection.  相似文献   

8.
Sixteen calves approximately 6 months old were each infected with 500 metacercariae of Fasciola hepatica. Thirty-two days later they were weighed and divided into two groups, and on day 35 all calves in one of the groups were injected subcutaneously with an ivermectin/closantel combination. Both groups were sacrificed between days 70 and 72 to enable counting and examination of the flukes recovered from the bile ducts. Eggs released by the flukes were collected for incubation, hatching and estimation of egg viability. Flukes were counted, flat-fixed in 70% ethanol, stained with catechol and carmine and measured. The reproductive organs, namely testis, vitelline glands, ovary and uterus, were examined and scored on a 0-3 scale according to their state of development. This was visually assessed on the basis of size, distribution and staining density of their constituent tissues and the abundance of eggs in the uterus. A representative sample of flukes from each animal was fixed in formalin for histological sectioning to enable more detailed examination of the reproductive structures. Treatment of the immature flukes reduced the population in cattle by 42.6% as compared with the controls and as a result of the stunting effect due to the presence of closantel during early development the size of treated flukes was reduced by 43.9%. A bimodal pattern of size and reproductive score was also observed in flukes from treated cattle, suggesting that the stunting effect on individual flukes differed depending on whether or not they had gained access to the bile ducts or were still migrating in the hepatic parenchymal tissue at the time of drug exposure with the effect being greater once the fluke had gained access to the bile ducts. The mean reproductive score for untreated flukes was 8.76 and for treated flukes 5.64, a 35.6% reduction. This difference was highly significant (p<0.001). Egg shedding from treated flukes was significantly less than that from controls (p<0.05), but there were no differences in hatchability, suggesting that whilst drug treatment reduced the energy supply available for gametogenesis/oogenesis, it did not induce functional defects in the gonads or accessory reproductive organs. Histological examination confirmed that there was a reduction in development of testes, ovaries and vitellaria in treated flukes, with a consequent reduction in egg production. In the treated flukes, early spermatogonia and oogonia were the predominant cell types in the testes and ovary, whilst undifferentiated stem cells were abundant in the vitelline follicles. In untreated flukes, cells representing more advanced stages in gametogenesis and vitellogenesis predominated in the respective organs. It is likely that this inhibition of gametogenesis and vitellogenesis was caused by the effects of closantel treatment on intermediary metabolism in the flukes. Clearly these effects were evident even at a relatively early stage of fluke growth, and because of the impact on egg output may have epidemiological importance in addition to the reduction in fluke numbers.  相似文献   

9.
The efficacy of clorsulon and of albendazole against Fascioloides magna were evaluated in 36 naturally infected white-tailed deer (Odocoileus virginianus) in southern Texas. A single oral dose of clorsulon suspension (12 to 30 mg/kg of body weight; mean = 24 mg/kg) was given to each deer and killed 153 (92%) of 167 mature flukes and 4 (80%) of 5 immature flukes recovered at necropsy. A single oral dose of albendazole paste (17 to 46 mg/kg; mean = 26 mg/kg) was given to each deer and killed 148 (89%) of 167 mature flukes and 4 (67%) of 6 immature flukes recovered at necropsy. In 82 nontreated control deer, 271 live flukes were recovered; dead flukes were not recovered.  相似文献   

10.
The pharmacokinetics of oxyclosanide, rafoxanide and closantel were investigated in sheep (n = 5). All three drugs were extensively (greater than 99%) bound to plasma proteins and the plasma concentration/time curve was best described by a tri-exponential equation. Closantel and rafoxanide had long terminal half-lives (mean 14.5 and 16.6 days, respectively) compared with oxyclosanide (mean 6.4 days). In a study of the efficacy of rafoxanide against Fasciola hepatica, a dose rate of 7.5 mg kg-1 against 6-week-old flukes appeared to be similarly effective to a dose rate of 2.5 mg kg-1 against 10-week-old flukes (86% and 88% efficacy, respectively), as assessed at autopsies carried out on all sheep when the flukes were 14 weeks old. Part of this putative efficacy against immature flukes may be due to rafoxanide persisting in the plasma and affecting the mature flukes when they reach the bile ducts.  相似文献   

11.
The relative importance of peak level- and residual level-related flukicidal activity of closantel against immature and mature Fasciola hepatica was evaluated in a comparative efficacy trial using two animal species with a different plasma elimination pattern, that is, the rat and the sheep with an elimination half-life of less than one week and of two to three weeks, respectively. The rats were dosed orally with closantel at 20 mg kg-1 at two, four, six, eight and 10 weeks; the sheep at 10 mg kg-1 at eight, 10 and 12 weeks after artificial infection. Necropsy was performed either one week after treatment or 12 weeks after infection. Efficacy rates and the length of the recovered flukes were evaluated. It was demonstrated that the flukicidal effect of closantel is directly related to its peak plasma levels and less to its residual plasma concentrations. In the rat, a high efficacy (P less than 0.001) could be demonstrated against immature stages of four weeks or older. The two-week immature stages were less markedly affected. No significant differences in efficacy and size of the flukes were noted between the animals autopsied one week after treatment and those autopsied 12 weeks after infection. In the sheep, the efficacy against six-week and eight-week-old immature stages varied between 70.3 and 76.8 per cent and between 92.8 and 96.5 per cent, respectively. As in the rats, no marked differences in efficacy were noted between the animals autopsied one week after treatment and those autopsied 12 weeks after infection.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

12.
An in vivo study in the laboratory rat model was carried out to monitor morphological changes in adult Fasciola hepatica over a 4-day period resulting from combination treatment of triclabendazole (TCBZ) and the metabolic inhibitor, ketoconazole (KTZ). Rats were infected with the TCBZ-resistant Oberon isolate of F. hepatica and divided into 3 groups at 12 weeks post-infection. The first group was dosed orally with TCBZ at a dosage of 10mg/kg and KTZ at a dosage of 10mg/kg. Flukes were recovered at 24, 48, 72 and 96 h post-treatment (p.t.). A second group of rats was treated with TCBZ alone (10mg/kg) and sacrificed at 96 h p.t. The third group acted as untreated controls. Surface changes were monitored by scanning electron microscopy (SEM). In flukes from the TCBZ+KTZ-treated group, the results showed a progressive and time-dependent increase in the level of disruption to the tegumental syncytium. Swelling, furrowing, blebbing and sloughing of the syncytium increased with time p.t. Another feature seen was a thick layer of tegumental shedding in some fluke samples at different times p.t. By comparison, flukes treated with TCBZ alone remained unaffected. The results demonstrated that the Oberon isolate is only sensitive to drug action in the presence of ketoconazole, indicating that combining triclabendazole with a metabolic inhibitor could be used to preserve the effectiveness of the drug against TCBZ-resistant populations of F. hepatica.  相似文献   

13.
Investigation of the triclabendazole (TCBZ) resistance status of populations of Fasciola hepatica in field cases of fasciolosis, where treatment failure has been reported, can be supported by histological examination of flukes collected from recently treated hosts. In TCBZ-sensitive flukes (TCBZ-S) exposed to TCBZ metabolites for 1–4 days in vivo, but not in TCBZ-resistant flukes (TCBZ-R), morphological changes suggestive of apoptosis occur in cells undergoing meiosis or mitosis in the testis, ovary and vitelline follicles. In order to verify or refute the contention that efficacy of TCBZ treatment is associated with apoptosis in the reproductive organs of flukes, histological sections of TCBZ-S (Cullompton isolate) flukes and TCBZ-R (Sligo isolate) flukes were subjected to the TdT-mediated dUDP nick end labelling (TUNEL) in situ hybridisation method, a commercially available test specifically designed to label endonuclease-induced DNA strand breaks associated with apoptosis. Additionally, sections of in vivo-treated and untreated flukes originating from field outbreaks of suspected TCBZ-S and TCBZ-R fasciolosis were labelled by the TUNEL method. It was found that in treated TCBZ-S flukes, strong positive labelling indicating apoptosis was associated with morphologically abnormal cells undergoing mitosis or meiosis in the testis, ovary and vitelline follicles. Background labelling in the positive testis sections was attributed to heterophagy of cell debris by the sustentacular tissue. The triggering of apoptosis was probably related to failure of spindle formation at cell division, supporting the contention that TCBZ inhibits microtubule formation. In treated TCBZ-R (Sligo Type 1) flukes, and in treated flukes from field outbreaks of suspected TCBZ-R fasciolosis, no significant labelling was observed, while sections of fluke derived from a field case of fasciolosis where TCBZ resistance was not suspected were heavily labelled. Light labelling was associated with the testis of untreated Cullompton (TCBZ-S) and Sligo Type 2 (TCBZ-R) flukes, which exhibit abnormal spermatogenesis and spermiogenesis, respectively. This was attributed to apoptosis and to heterophagy of effete germ line cells by the sustentacular tissue. It is concluded that demonstration of apoptosis by in situ hybridisation using the TUNEL method on sections of 1–4 days in vivo TCBZ-treated F. hepatica can contribute to the diagnosis of TCBZ resistance in field outbreaks of fasciolosis.  相似文献   

14.
AIMS: To measure the efficacy of a pour-on formulation of moxidectin against lungworm and abomasal parasites in weaner wapiti x red deer and to compare this with its efficacy in weaner red deer. METHODS: Six red and six wapiti hybrid deer, naturally infected with lungworm and gastro-intestinal parasites, were treated with pour-on moxidectin at 500 microg/kg body weight and slaughtered 14 or 16 days later, along with six red and six wapiti hybrid untreated control deer. Total worm counts were performed on the lungs, abomasum and abomasal digest of each deer. RESULTS: The efficacy of moxidectin pour-on was 100% against adult and immature lungworms (Dictyocaulus viviparus) in red deer, and 100% and 99.7% effective against adult and immature lungworm in wapiti hybrid deer. The efficacy of moxidectin pour-on was 100, 100, 99.9 and 99.9% respectively against adult, fifth stage, late fourth stage and early fourth stage larvae of Ostertagia-type nematodes (assumed to be Ostertagia, Spiculopteragia, Skrjabinagia and Apteragia spp.) in both red and wapiti hybrid deer. CONCLUSIONS: The pour-on formulation of moxidectin, at 500 microg/kg body weight, is highly effective against mature and immature lungworms and abomasal nematodes in wapiti hybrid deer and equally effective in red deer.  相似文献   

15.
Two separate field trials involving naturally infected cattle were carried out on two farms known to have a history of Fasciola hepatica infection. On the first farm, 15 animals per group were allocated as follows: G1, triclabendazole (TCBZ) four times a year; G2, TCBZ twice a year (May and September); G3, untreated control. All groups grazed together and after 3.5 years the animals were slaughtered and their livers examined by federal meat inspectors who condemned 100% of livers in G3 and 8.3% in G2 owing to the presence of lesions of fasciolosis. In G1 no livers were condemned. Significant differences in weight gains were not detected and fluke counts remained at low levels in the treated groups. Also, in the control group, egg counts started to decrease when animals were 2 years old. On the second farm, groups of 20 animals were treated as follows: G1, TCBZ three times a year (May, September and December); G2, TCBZ twice a year (May and September); G3, nitroxynil twice a year (May and September); G4, rafoxanide twice a year (May and September); G5, untreated controls. All animals were weighed and faecal samples examined at approximately 28-day intervals. During the period of the study, larger weight gains were detected in the TCBZ treated groups than in the others. TCBZ treatment kept F. hepatica egg counts at a lower level for longer periods than the other drugs and significant differences in weight gains were only obtained between the group receiving TCBZ three times a year and the control group.  相似文献   

16.
Fascioliasis causes important economic losses in ruminant species all over the world. Its control is largely based on the use of the flukicidal compound triclabendazole (TCBZ). However, its chemically related benzimidazole anthelmintic albendazole (ABZ) is being successfully used to control TCBZ-resistance flukes. This research gains some insights into the comparative molecular behaviour of both anthelmintics within the target fluke. The goals of the current work were: (i) to assess the competitive binding of ABZ and TCBZ to cytosolic proteins of F. hepatica, and (ii) to evaluate the enantioselective biotransformation of ABZ in microsomal fractions obtained from TCBZ-susceptible and TCBZ-resistant strains of the liver fluke. Cytosolic proteins from fluke specimens bound TCBZ with greater affinity (83%) than ABZ (44%) and the fraction of TCBZ bound to cytosolic proteins was not displaced by ABZ. The microsomes from both -susceptible and resistant flukes sulphoxidized ABZ into ABZ sulphoxide (ABZSO). However, this oxidative activity was 49% higher in microsomes from TCBZ-resistant flukes (P < 0.001) with a predominant production of the (+) ABZSO enantiomer. As earlier shown for TCBZ, the results reported here confirm an enhanced ability for ABZ oxidation in TCBZ-resistant flukes. While this enhanced oxidative metabolism of ABZ may cooperate to the resistance phenomenon, other pharmacodynamic-based mechanisms may be involved, which would explain why, although being chemically-related, ABZ remains efficacious against TCBZ resistant flukes under field conditions.  相似文献   

17.
The objective of the present studies was to evaluate the efficacy of a combined formulation (Startect(?) Dual Active Oral Solution for Sheep, Pfizer Animal Health) of derquantel (DQL) and abamectin (ABA) for the treatment of: (1) sheep experimentally infected with a moxidectin (MOX)-resistant isolate of Teladorsagia circumcincta, and (2) multi-drug resistant gastrointestinal nematode parasites under UK field conditions. In the first study, a total of 40 animals were allocated into 4 treatment groups, and were either left untreated or treated with DQL+ABA, MOX or ABA. Faecal samples were collected on days 1-5 and on day 7 after treatment to examine the reduction in faecal egg excretion and to evaluate the egg viability. On day 14 post treatment all animals were euthanised for abomasal worm counts. There was a 100% reduction in geometric mean worm counts for the DQL+ABA treated animals compared to the untreated control animals (P<0.0001), whereas the percentage reduction in worm counts for the MOX- (P>0.05) and ABA-treated (P=0.0004) animals was 12.4% and 71.8%, respectively. The data from the egg hatch assay (EHA) indicated that in the MOX-treated and the ABA-treated animals, the majority of the eggs hatched after treatment. In the field study, performed on four farms, animals were allocated into 6 groups of 11-15 animals each in order to conduct a faecal egg count reduction test (FECRT), based on arithmetic mean egg counts. One group of animals remained untreated, whereas the other animals were treated with DQL+ABA, MOX, fenbendazole (FBZ), levamisole (LV) or ivermectin (IVM). On each of the farms the reduction in egg excretion after treatment with FBZ, LV or IVM was below 95.0%, indicating anthelmintic resistance. The efficacy of DQL+ABA ranged from 99.1 to 100%, yielding significantly lower egg counts compared to the untreated control group (P≤0.003). For MOX the egg counts were significantly (P≤0.003) lower compared to the untreated group at each farm, with reductions varying from 98.2 to 100%. The post-treatment copro-cultures for larva identification indicated that T. circumcincta was the most abundant worm species after treatment (52-99% of the larvae). The results of these studies confirm the high efficacy of the DQL+ABA combination formulation against anthelmintic resistant nematodes in the UK.  相似文献   

18.
《Veterinary parasitology》2015,207(1-2):134-139
Recently, sharp increases in the prevalence of rumen fluke infections have been recorded throughout Western Europe. However, scarce information is available on the diagnosis, pathogenic importance and control of this parasite. We undertook 3 pilot studies to gain more insights into these aspects of rumen fluke biology in cattle. First, we evaluated the diagnostic performance of mini-FLOTAC to detect adult rumen fluke infections based on faecal egg count in an abattoir survey and found high sensitivity (0.94) and specificity (0.98). Moreover, there was an association between ruminal fluke burden (assessed by visual scoring) and faecal egg count and a cut-off of 200 eggs per gram is proposed to detect highly infected animals (>200 flukes present in the rumen and/or reticulum). There was also a significant association between ruminal fluke burden and faecal consistency. However, in a second study, we performed a case-control field survey to investigate the association between rumen fluke infection and herd-level problems with diarrhoea and no association was found. Finally, we evaluated the use of closantel (Flukiver®, Elanco Animal Health, subcutaneous administration at 10 mg/kg) to treat rumen fluke infection on 3 herds, but no significant reduction in egg output post-treatment was found. Because this result is in contrast with a previous study using an oral dose of closantel, more research is required into the effect of administration route on the efficacy of closantel on rumen fluke.  相似文献   

19.
Two studies were conducted to determine the persistent efficacy of doramectin pour-on against an artificial, trickle challenge of mixed nematodes in calves. In each study, 42, 4-8 months old calves were randomly assigned into four groups of 10 animals each (T1-T4), plus two larval-viability monitor animals. All animals were treated with fenbendazole (10 mg kg(-1)) 14 days prior to the start of the study to clear any existing infection. Doramectin pour-on at 500 microg kg(-1) was used on each animal in Groups T2, T3, and T4 with intervals of 1 week (Day 0, 7, and 14, respectively). Calves in Group T1 were treated with saline solution on Day 0 and at the same volumetric rate (1 ml 10 kg(-1)) as the doramectin treated animals. All treatments were applied in a single passage along the midline of the back, from the withers to the tailhead. Subsequently, trickle inoculations with infective larvae were administered to all calves for 22 consecutive days (Days 14-35). Doramectin pour-on provided > or = 91.9% efficacy against challenge with Dictyocaulus viviparus, Haemonchus spp., and Ostertagia ostertagi for up to 35 days post-treatment and against challenge with Cooperia oncophora, Cooperia punctata, and Oesophagostomum radiatum for up to 28 days post-treatment.  相似文献   

20.
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   

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