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Publisher: Elsevier BV
Date: 08-2016
DOI: 10.1016/J.VETPAR.2016.06.017
Abstract: The eggs of some species of the parasitic nematode Nematodirus require a period of chilling before they can hatch N. filicollis is one such species. This study investigated this requirement for chilling in a New Zealand strain of this species. Eggs of N. filicollis were extracted from lamb's faeces and incubated at 20°C to allow development to the third stage larvae within the egg. These eggs were then placed into tissue culture plates and incubated at: 2.7°C (±0.99), 3.6°C (±0.90), 4.7°C (±0.35), 6.4°C (±0.37), 8.0°C (±1.54) or 9.9°C (±0.14) for up to 224 days. At 14day intervals until day 84, then every 28 days, one plate was removed from each temperature and placed at 13.1°C (±0.44) for 14 days. Eggs were then assessed for hatching. From this data, chill units were calculated by subtracting the culture temperature from a constant threshold of 11°C and multiplying by the number of days for which the s le was cultured then the Gompertz model fitted. Even though hatching overall was low, a greater proportion of eggs hatched with chill accumulation. Maximum hatching of eggs required 800-1000 chill units. Consequently in the field, more than one season of chilling would be required before hatching. As such a generation time could take more than one year to complete. This is different to the hatching dynamics of N. spathiger, the other main species found in New Zealand sheep, which does not display this requirement for chilling and hatches immediately once the third stage larvae are developed.
Publisher: Elsevier BV
Date: 04-1997
DOI: 10.1016/S0020-7519(96)00193-2
Abstract: Lactating adult Romney ewes were infected, 4 weeks post-lambing, with benzimidazole (bz) resistant strains of Ostertagia circumcincta and Trichostrongylus colubriformis. Commencing 4 weeks after the initial infection the ewes were subjected to challenge 3 times weekly with 5000 L3 of bz-susceptible strains of both parasite species. At weekly intervals over the following 6 weeks, groups of ewes were drenched with a bz anthelmintic (oxfendazole) to remove bz-susceptible parasites and slaughtered to determine adult worm burdens of the bz-resistant parasites. The O. circumcincta infection declined exponentially with a mean daily death rate of 10.6% day-1 and no worms were recovered after 4 weeks or more of challenge. The T. colubriformis infection did not decline significantly over the 6 weeks of continuous challenge, indicating that the death rate could not be distinguished from zero. The upper 95% confidence limit for the death rate of T. colubriformis was 4.9%. The implications of these death rates on selection for drug resistance following ewe drenching during the post-partum period are discussed with selection pressure likely to be greater for T. colubriformis than for O. circumcincta.
Publisher: Elsevier BV
Date: 07-1999
DOI: 10.1016/S0304-4017(99)00079-5
Abstract: One of three groups of sheep was challenged twice-weekly with infective-stage larvae (L3) of the sheep parasite O. circumcincta, another with the cattle parasite O. ostertagi while the third received no larval challenge. Positive faecal egg counts (FEC) and a rise in plasma pepsinogen levels were observed only in those animals given O. circumcincta. Anti-O. circumcincta L3 IgG titres were rapidly elevated during parasite challenge with either O. circumcincta or O. ostertagi. Throughout the experiment, no rise in anti-adult IgG titres or eosinophil numbers was observed in peripheral blood in any group. On evidence of self-cure of the trickle-infection, determined by a reduction in FEC, all groups were drenched and challenged with 15,000 O. circumcincta L3. No effect of previous challenge on parasite establishment or FEC was observed, although egg viability was significantly reduced in both groups given prior challenge. Significant differences in adult female worm length were observed between groups. Those recovered from animals previously challenged with O. circumcincta were shorter than from those given O. ostertagi which were in turn shorter than those from previously unchallenged animals. In utero egg counts were significantly lower in worms from animals previously challenged with O. circumcincta than in those from unchallenged control animals. The results indicate that a level of immunity to O. circumcincta can be conferred by exposure to O. ostertagi.
Publisher: Elsevier BV
Date: 02-1999
DOI: 10.1016/S0020-7519(98)00210-0
Abstract: The ability of lactating Romney ewes to resist establishment of ingested infective-stage larvae (L3) of Ostertagia circumcincta and Trichostrongylus colubriformis was measured in the field. Three groups of seven single-lamb-bearing ewes were selected on the basis of uniformity of lambing date from a large flock held on pasture. Either 2, 4 or 6 weeks after parturition, groups of ewes were dosed with 24000 L3 of known oxfendazole-resistant parasite strains 12000 of each species. Ten to 14 days later the ewes, along with their lambs, were transferred from the field to indoor pens. Twenty-five days after the challenge dose the ewes were drenched with oxfendazole to remove any field-derived infection and 3 days later slaughtered for worm counts. Mean establishment of the resistant parasites was low at all times, with the highest rate recorded being 6.1% for O. circumcincta 2 weeks after parturition. Establishment of O. circumcincta 4 and 6 weeks after parturition, and of T. colubriformis at all times, never exceeded 2%. By comparison, mean establishment in lambs held indoors and parasite free for 13 weeks prior to infection, was 24.9% and 47.1% for O. circumcincta and T. colubriformis, respectively. These results indicate that the lactating ewes were exhibiting a substantial ability to prevent establishment of ingested larvae. The results of this and other similar studies suggest that the dynamics of parasitism in lactating Coopworth and Romney ewes in New Zealand is substantially different to that in Merino ewes in Australia, and that these differences influence optimal strategies for the management of anthelmintic resistance in the two countries.
Publisher: Informa UK Limited
Date: 08-08-2014
DOI: 10.1080/00480169.2014.920700
Abstract: To compare the prevalence of Nematodirus spathiger and N. filicollis on a s le of farms in the lower South Island with the lower and central North Island of New Zealand by way of a presence/absence survey. A presence/absence non-random survey was conducted in which pooled faeces from lambs from 50 farms in the lower and central North Island (n=22) and lower South Island (n=28) were cultured, with and without a post-culture period of chilling, to produce third-stage parasitic nematode larvae (L3). After recovery using the Baermann technique, in idual L3 were identified to Nematodirus spp. using a PCR assay. This identified the species that were present on each farm that were then used to compare the regions. Nematodirus filicollis was present in 38/50 (76%) s les from which Nematodirus spp. larvae were cultured, compared with 50/50 (100%) in the case of N. spathiger. No regional differences were observed in the prevalence of either species (p=0.74). Of the Nematodirus spp. L3 recovered from the unchilled s les, 415/428 (97%) were N. spathiger and 13/428 (3%) N. filicollis. After chilling 594/695 (85%) of the Nematodirus spp. L3 were N. spathiger and 101/695 (15%) were N. filicollis. Despite the non-random nature of the study, the evidence suggests that both these species are likely to occur sympatrically on most sheep farms throughout New Zealand. In general N. filicollis eggs did not hatch without a period of chilling and this has implications for the identification of these larvae using conventional culture methods.
Publisher: Elsevier BV
Date: 12-2018
DOI: 10.1016/J.VETPAR.2018.11.001
Abstract: The establishment rate of Cooperia oncophora related to host age and previous infection was investigated in young calves. Calves of similar age were kept on a feed pad and allocated into multiple groups, based on their age and weight. Two groups (each n = 16) received trickle infections with an ivermectin-susceptible C. oncophora isolate of 2000 or 10,000 infective stage larvae per week while another group (n = 16) was kept as an uninfected control. At intervals over a period of 11 months, two animals from each group were challenged with 15,000 infective stage larvae of an ivermectin-resistant isolate, 25 days later orally treated with ivermectin and 5 days after that slaughtered for worm counts. On three occasions additional calves (n = 2), subjected to the high trickle infection rate, received an ivermectin treatment to remove the existing worm burden, prior to challenge as above. Further calves (n = 4) of similar age were introduced at the beginning and the end of the experiment to determine the effect of larval age on establishment rate. The establishment in the two trickle infection groups declined to <10% within the first three months, which was significantly different from the control group. In the animals receiving the high trickle infection, but an anthelmintic treatment before challenge the establishment rate was not significantly different from the controls. Over the duration of the experiment establishment in the control group declined from 53% to <20%, which was similar to the decrease recorded at the beginning and the end of the experiment in the animals to determine the effect of larval age. The findings indicate that an existing C. oncophora burden had a strong effect on the establishment of incoming larvae in the trickle infected groups, but this was not observed if the existing burden was removed before the final challenge. The decline in establishment rate in the control group was attributed to the age of the larvae and not the age of the calves per se.
Publisher: Cambridge University Press (CUP)
Date: 10-2002
DOI: 10.1017/S0031182002002184
Abstract: Nine groups of lambs were challenged with 500 drug-resistant (R) Ostertagia circumcincta infective-stage larvae (L3) twice-weekly for 6 weeks 3 of the groups were also given 500 susceptible (S) L3 and another 3 given 3000 L3 twice-weekly. One week prior to parasite challenge, 1 group of each dose rate was administered ivermectin-capsules (IVM-CRCs). Following challenge, a second group from each dose rate was administered oxfendazole to remove susceptible parasites. The remaining groups received no drug treatment throughout the trial. No significant difference in faecal egg count was observed between the groups. The groups left untreated did not differ significantly in resulting worm burden. However, the percentage of the total L3 challenge recovered as 4th-stage larvae or adult worms demonstrated a density-dependent relationship and declined with increasing challenge. Those groups treated with anthelmintic to remove S worms prior to necropsy also showed density dependency as worm burdens were lower at the highest dose rate. In the groups administered IVM-CRCs, no dose-dependent effect on worm burden was observed. These differences resulted in more worms being present at the highest dose rate in the IVM-CRC-treated animals than in those animals treated orally with anthelmintic. Adult female worms from the IVM-CRC high challenge group were significantly longer and contained more eggs in utero than those in the other high challenge groups. These results demonstrate that where resistance is present, IVM-CRCs can modify the density-dependent regulation of the parasite population, resulting in the acquisition of larger resistant worm burdens than might otherwise be expected. This could accelerate the build-up of resistant worm populations and decrease the time until treatment failure.
Publisher: Informa UK Limited
Date: 10-2007
DOI: 10.1080/00480169.2007.36773
Abstract: To report current farmer opinions and farming practices relating to control of gastrointestinal nematodes and anthelmintic resistance on sheep farms in New Zealand. An interview-based cross-sectional study of grazing management and anthelmintic usage was conducted by veterinarians on 80 randomly selected sheep farms in New Zealand. Useable data were returned by 74/80 (92%) farmers who participated in the study. However, despite contacting 400 farmers the target s le size of 100 farms was not reached. The results indicated that only 31% of farms had previously tested for drench resistance, that effective quarantine-drenching of imported stock was not always carried out, and that farmers were more likely to integrate cattle than ewes into their grazing management of lambs. Furthermore, the number of drenches given to lambs had changed little in 25 years. The use of faecal egg counting by farmers has increased. Dependence on anthelmintics continues to be high on sheep farms in New Zealand. Whilst the number of drench treatments has changed little, there is more widespread use of persistent or long-acting treatments. Farmers need to be encouraged to monitor the resistance status of nematode populations on their farms and use this information to develop strategies aimed at maintaining susceptible alleles within the parasite populations and conserving the efficacy of existing drug families.
Publisher: Elsevier BV
Date: 08-2003
DOI: 10.1016/S0304-4017(03)00186-9
Abstract: Sixty-four Romney ewe lambs were allocated to 12 groups on the basis of liveweight. Four groups (n=5) were administered oral ivermectin (IVM), 4 (n=6) oral moxidectin (MOX) and the remaining 4 (n=5) controlled-release capsules containing IVM (IVM-CRCs). Nine and 10 days later, the groups within each treatment type were challenged with infective-stage larvae (L3) of 1 of 4 different isolates of Teladorsagia circumcincta (two doses each of 5000 L3). The first of these (S) was known to be anthelmintic-susceptible the second (OR) was a multiple anthelmintic-resistant strain recovered from the field following therapeutic failure of both ivermectin and moxidectin and subsequently maintained in the laboratory without further anthelmintic selection the third (R) was derived from OR but had been passaged for five generations indoors with each generation being screened with all three broad-spectrum anthelmintic classes and the fourth (RxS) was an F1 cross between the R and S isolates. As anticipated, because of its limited residual activity, IVM had no significant effect on the establishment, 9 and 10 days post-treatment, of any of the parasite isolates. In contrast MOX, which has greater residual activity, was highly effective at preventing the establishment of the S isolate but showed no significant effect against the OR, R or RxS isolates. The IVM-CRC was also highly effective at preventing the establishment of the S isolate and furthermore it significantly reduced establishment of both the OR and RxS isolates, although it had no significant effect against the R isolate. The results suggest that with respect to the establishment of T. circumcincta L3s following anthelmintic treatment, macrocyclic lactone (ML) resistance is effectively a dominant trait in the presence of MOX, while it behaves as a partially dominant/recessive trait under treatment with IVM-CRCs. The potential implications of this finding in relation to selection for ML resistance in T. circumcincta are discussed.
Publisher: Elsevier BV
Date: 09-1998
DOI: 10.1016/S0020-7519(98)00092-7
Abstract: Variation between hosts of different ages and genotypes in the developmental success of trichostrongylid parasite eggs from sheep was investigated in two trials. The percentage development to infective third-stage larvae of eggs collected from lambs and adult ewes infected with Ostertagia circumcincta was compared in an indoor trial. In addition, sheep previously bred for either high or low faecal egg count and grazed outdoors on parasite contaminated pasture were s led egg development, faecal egg count, generic profile and faecal dry matter were measured. In both trials, development to L3 was significantly lower in eggs derived from adult ewes than from lambs and, in the field trial, from animals selected for low faecal egg count. The observed differences could not be accounted for by variations in faecal egg count, faecal dry matter content nor by differences in the generic composition of worm egg output. Although not shown conclusively, the results are consistent with an immune mechanism influencing the development of free-living stages of gastrointestinal nematodes outside the host. These results have significant implications for our understanding of parasite epidemiology, particularly as it relates to sources of pasture contamination.
Publisher: Elsevier BV
Date: 2001
Abstract: Acceptable performance of grazing cattle frequently depends on the availability of effective broad-spectrum anthelmintics to remove, or prevent infection with, gastrointestinal nematodes. This control is increasingly threatened by populations of nematodes resistant to the most commonly used anthelmintics. Although this appears to have developed more slowly than in nematodes infecting small ruminants, the number of reports in the literature over the past five years suggests a rapidly escalating problem. This review discusses this literature, several issues unique to cattle parasitism and anthelmintics, and how previous research in small ruminants can improve the management of anthelmintic resistance in cattle.
Publisher: Elsevier BV
Date: 03-1997
DOI: 10.1016/S0020-7519(96)00183-X
Abstract: Two experiments were carried out to evaluate a larval development assay for the detection of anthelmintic resistance in O. circumcincta. In Experiment I, the dose responses to levamisole (LEV), thiabendazole (TBZ) and ivermectin (IVM) of 8 isolates of O. circumcincta were measured 34 days after infection (DAI). Four of these isolates were shown to be resistant to 1 or more anthelmintics. With 2 exceptions, all isolates considered to be resistant had higher LD50 values than the susceptible isolates for that anthelmintic. One exception was isolate RM8, which was considered to be resistant to all 3 anthelmintics based on faecal egg count reduction tests in goats, but the LD50 value for LEV did not differ from that for the susceptible isolates. The other exception was an isolate considered to be susceptible to TBZ which had a relatively high LD50 value. In an unrelated trial that was prompted by this finding, this isolate was confirmed to be benzimidazole-resistant. Isolate RM8 and an isolate susceptible to all 3 anthelmintics (SK2) were used in the second experiment, which was conducted to monitor changes in the LD50 values of LEV, TBZ and IVM over time following a single infection of 35,000 infective larvae in young sheep. Faecal s les were collected weekly from 24 to 115 DAI. With all 3 anthelmintics, the LD50 values increased with time to a peak around 50-60 DAI, and then declined to levels similar to those observed soon after patency. This trend was consistent for both isolates. The highest mean LD50 values for isolates SK2 for IVM and TBZ and RM8 for IVM and RM8, respectively, were 1.7 and 1.8 times, and 2.2 and 2.9 times higher than the initial mean LD50 values. There was a clear distinction in LD50 values between isolates at each s ling day for both IVM and TBZ. However, as a consequence of the changes in LD50 values with time, the peak LD50 values of IVM for isolate SK2 were higher than the minimum LD50 values of isolate RM8. As there was no apparent difference in LEV efficacy between these 2 isolates, the data were pooled. The highest mean LD50 value was 2.3 times higher than the initial LD50 value.
Publisher: Cambridge University Press (CUP)
Date: 07-2000
DOI: 10.1017/S0031182099006095
Abstract: We review the literature on parameter values relevant to the epidemiology of strongyle nematode infections of domestic sheep. Information is sub ided by parasite genus, country of origin and climate type. While field observations have been made in a large number of countries, the bulk of studies under controlled conditions have been conducted in Australia, New Zealand and the UK. For these countries, experiments and parameters are interpreted in terms of a previously published model of nematode dynamics, and are used to calculate the basic reproduction number. Average values range from less than 6 for Haemonchus contortus in New Zealand and a winter rainfall region of Australia, to more than 16 for Ostertagia circumcincta in New Zealand and the UK. Additional considerations of the effects of climate and the annual replacement of host stock show that for conditions favourable for parasite transmission this is a robust indicator of parasite epidemiology. When climate variation and annual replacement are added to the model, it is shown to reasonably describe the qualitative behaviour of an experimental data set, indicating it to be a useful tool for further investigation of some of the underlying assumptions of sheep–nematode dynamics.
Publisher: Springer Science and Business Media LLC
Date: 2003
Abstract: Challenge with an equal mix of drug-resistant and drug-susceptible larvae of Teladorsagia circumcincta resulted in infections in groups of lambs (n = 6) either untreated or given controlled-release capsules, containing either albendazole or ivermectin. Lambs treated with albendazole capsules contained similar numbers of adult worms at necropsy to the other groups but had no detectable faecal egg count. Animals treated with ivermectin capsules had similar worm burdens and faecal egg counts to the control group but the worms had significantly higher numbers of eggs in utero. These results provide evidence for suppression of egg production by both anthelmintic treatments. The observation that albendazole caused a significant reduction in the developmental success of parasite eggs also has implications for the use of faecal egg count as an indicator for pasture contamination with resistant parasites. In two further groups of lambs, either untreated or given albendazole capsules, treatment caused a significant reduction in egg count and adult worm burden of Trichostrongylus colubriformis. No significant effects were observed on in utero egg counts or egg viability and the apparent effect on the number of eggs produced in faeces per adult female was not significant (p = 0.077). There was, therefore, no evidence that albendazole controlled-release capsules caused suppression of egg output in this species.
Publisher: Informa UK Limited
Date: 06-2001
Publisher: Informa UK Limited
Date: 12-2006
DOI: 10.1080/00480169.2006.36711
Abstract: To establish the prevalence of anthelmintic resistance in parasitic nematodes on a random s le of beef cattle herds in the North Island of New Zealand. A cross-sectional prevalence study was conducted using a standardised faecal nematode egg count (FEC) reduction (FECR) test (FECRT) for ivermectin, levamisole and albendazole on 60 calves on each of 62 farms in the North Island chosen at random from farms that conformed with the selection criteria. Resistance to an anthelmintic was inferred when there was or =95% reduction in FEC for all anthelmintics tested. Resistance to ivermectin was evident on 56/61 (92%) farms, to albendazole on 47/62 (76%) farms, and to both ivermectin and albendazole on 45/61 (74%) farms. Resistance to levamisole was evident on only 4/62 (6%) farms. The parasites most prevalent in resistant populations cultured were Cooperia spp. On 45/61 (74%) farms where Cooperia spp were present in sufficient numbers, resistance to both ivermectin and albendazole was evident. No cases of levamisole-resistant Cooperia spp were detected. Resistance of Ostertagia spp to ivermectin was evident on 4/45 (9%) farms, to albendazole on 15/46 (35%) farms, and to levamisole on 4/46 (9%) farms. Anthelmintic resistance in parasitic nematodes of cattle is common in the North Island of New Zealand. Beef farmers need to be aware of the risks posed by anthelmintic resistance, and routine FECR testing is recommended to ensure optimal productivity and to guide decision-making when purchasing anthelmintics to be used on-farm.
Publisher: Wiley
Date: 1999
DOI: 10.1046/J.1365-2885.1999.00188.X
Abstract: In order to determine whether the efficacy of moxidectin against Ostertagia circumcincta is enhanced by its persistency, therapeutic efficacy was compared at intervals after treatment and with that of ivermectin, a closely related but more transient endectocide. Groups of 7-month-old New Zealand Romney lambs were infected with a strain of O. circumcincta known to be resistant to moxidectin. At patency of the infections, groups of lambs were treated with either moxidectin or ivermectin at the manufacturer's recommended dosages, or left untreated. At 3, 6 and 10 days post-treatment, faecal egg count was measured and groups of lambs were slaughtered for estimation of adult worm burden. Drug-resistant worm burdens were significantly reduced in those animals treated with moxidectin but not in those treated with ivermectin. No effect of time of slaughter on worm burden was observed with either drug, demonstrating that the higher therapeutic efficacy of moxidectin against this parasite was not due to an increased period of drug exposure. Faecal egg counts in the moxidectin treated animals increased with time after treatment indicating a temporary suppression of egg output by surviving worms. The implications of these findings on selection for anthelmintic resistance are discussed.
Publisher: Informa UK Limited
Date: 12-2006
DOI: 10.1080/00480169.2006.36710
Abstract: To establish the prevalence of anthelmintic resistance in parasitic nematodes on sheep farms in New Zealand. A cross-sectional prevalence study was conducted, using a standardised faecal nematode egg count (FEC) reduction (FECR) test (FECRT) for ivermectin, at a full (0.2 mg/kg) and half (0.1 mg/kg) dose rate, and albendazole, levamisole and albendazole-levamisole in combination, on 60 lambs (n=10 per group) on farms selected from throughout New Zealand. Farms that conformed with selection criteria were chosen at random (n=80) or with a history of suspected resistance to macrocyclic lactone (ML) anthelmintics (n=32). Resistance to an anthelmintic was inferred when there was or =95% FECR for all anthelmintics tested resistance to ivermectin at 0.1 and 0.2 mg/kg liveweight was evident on 36% and 25% of these farms, respectively. Resistance to both ivermectin (0.2 mg/kg) and levamisole was evident on 8/80 (10%) farms, to ivermectin and albendazole on 10/80 (13%) farms, and to ivermectin, levamisole and albendazole on 6/80 (8%) farms. The prevalence of resistance to a half dose of ivermectin tended to be more prevalent on farms with a history of suspected ML resistance (p=0.06). Resistance to albendazole was seen across all the main parasite genera, and to levamisole in Nematodirus, Ostertagia (= Teladorsagia) and Trichostrongylus species. Resistance to ivermectin was dominated by Ostertagia spp, although Cooperia, Nematodirus and Trichostrongylus species were also implicated. Anthelmintic resistance in parasitic nematodes of sheep is common in New Zealand. Not only was resistance to albendazole and levamisole common, but resistance to the ML, ivermectin, was at a higher prevalence than expected. Sheep farmers and advisors in New Zealand need to re-evaluate the way they manage parasites, and more research is urgently needed if the steady decline in anthelmintic susceptibility is to be halted.
Publisher: Informa UK Limited
Date: 12-2001
DOI: 10.1080/00480169.2001.36237
Abstract: Anthelmintic resistance was first confirmed in New Zealand in 1979 and since then has become common-place more than 50% of sheep farms now have detectable levels of resistance to one or more chemical classes of anthelmintic. Farmer drenching practices have changed little over the last 15-20 years and are clearly exerting a significant level of selection for resistance. In the absence of new chemical classes of anthelmintics, current parasite control practices will be unsustainable in the long-term. Once substantial resistance has developed, significant reversion to susceptibility is unlikely and re-introduction of failed drugs is likely to result in the re-emergence of control problems. The number of anthelmintic treatments applied is not necessarily a reliable indicator of selection pressure and should not be the only factor considered in strategies for minimising the development of resistance. The relative potential of the different anthelmintics now available, particularly the long-acting products, to select for resistance varies with the way they are used and with other epidemiological and management factors generalisations about their respective roles in the development of resistance are often unreliable. In many cases, literal extrapolation of recommendations for the management of resistance from Australia to New Zealand is unsupportable, given the differences in climate, parasite ecology and farming practices between the 2 countries. In the absence of a refuge for susceptible genotypes, as occurs when anthelmintic treatments are used as a means of generating low-contamination 'safe' pasture for young stock, the rapid development of resistance is likely. Anthelmintic treatments applied to animals with a high level of immunity, or which become immune while the anthelmintic is active, are likely to select for resistance faster than treatments applied to non-immune stock.
Publisher: Informa UK Limited
Date: 02-2006
DOI: 10.1080/00480169.2006.36599
Abstract: To assess the in vivo anthelmintic activity of condensed tannins (CT) in the forage species Dorycnium rectum and Medicago sativa, and in an extract from grape (Vitus vinifera) seeds (GSE), against two species of parasite, Teladorsagia (Ostertagia) circumcincta and Trichostrongylus colubriformis, at different stages of their life cycle, in sheep that were parasite-naïve or previously exposed to nematodes. In Trial 1, a factorial treatment structure was used to compare faecal nematode egg counts (FEC) and worm burdens in 40 weaned Romney lambs fed either the CT-containing forage D. rectum (12% dry matter DM) or M. sativa (lucerne 0.2% DM). Twenty naïve and 20 previously-exposed lambs were drenched free of parasites then reinfected with known species and numbers of parasites, and housed in pens indoors on a diet of lucerne pellets and chaffed hay. Groups of lambs (n=5 lambs per group) were fed one of the forages over one of two time periods within the parasite's life cycle. Six to nine days after the last feeding of fresh forages, faecal s les were collected for FEC, and all lambs were slaughtered and worm counts conducted. In Trial 2, 12 Suffolk x Romney lambs were surgically implanted with an abomasal cannula and then housed indoors in metabolism crates. After infection with parasites, six lambs were infused continuously over a 14-day period with a commercially available CT GSE (96% DM, made up to 34 g/L in water) the remaining lambs were infused with water. During infusion, s les were collected for egg hatch and larval development assays. After infusion, s les were collected for FEC, and all lambs were slaughtered and worm counts conducted. In Trial 1, there was a significant (p<0.001) difference in burdens of O. circumcincta between naïve lambs and those previously exposed to parasites, but no other differences were recorded. In Trial 2, lambs infused with GSE had significantly (p<0.05) fewer T. colubriformis at slaughter and significantly (p<0.001) fewer eggs hatched in the egg hatch assay (EHA) than for lambs infused with water. Overall, the differences attributable to GSE were small in magnitude, being an 11% drop in egg hatch, and an 18% drop in numbers of adult T. colubriformis after 14 days of continuous infusion. No other differences were recorded. The results indicate that the in vivo anthelmintic activity of these CT sources is, at best, modest and is unlikely to be of any practical value. Further, these data emphasise that in vitro activity is an unreliable indicator of in vivo efficacy for CT-containing forages and extracts.
Publisher: Wiley
Date: 08-1997
DOI: 10.1136/VR.141.5.120
Abstract: Three groups of newly-weaned Romney lambs were given either a standard oral dose of albendazole, a controlled-release capsule containing albendazole, or a standard oral dose of moxidectin. At 10, 20, 30 and 40 days after treatment, sub-groups of lambs were given 10,000 infective-stage larvae of either a drug-resistant or a drug-susceptible strain of Ostertagia circumcincta. The recommended oral dose of albendazole removed 32 per cent of the resistant strain and over 99.9 per cent of the susceptible O. circumcincta. The recommended oral dose of moxidectin removed 91 per cent of the resistant strain and over 99.9 per cent of the susceptible parasites. None of the lambs treated with controlled-release capsules was challenged at 20 or 30 days after treatment. Twenty-one days after challenge, s les of faeces were taken to determine the presence of nematode eggs and cultured to establish the proportion of eggs developing to infective-stage larvae (L3). Abomasa were recovered after slaughter and worm burdens determined. In the lambs given controlled-release capsules only the resistant parasites were able to establish, and there were significantly fewer than in the lambs treated orally with albendazole. The proportion of the eggs from resistant parasites which developed to L3 was not reduced by the presence of the capsules. Oral moxidectin provided no protection against the establishment of the resistant strain and viable L3 were recovered after challenge with resistant parasites 10 days after treatment however, the establishment of susceptible O. circumcincta was reduced by more than 99 per cent. The establishment of the susceptible parasites in the lambs treated with moxidectin increased with time and was not significantly lower than in the other groups by 30 days after treatment.
Publisher: Informa UK Limited
Date: 10-2000
DOI: 10.1080/00480169.2000.36183
Abstract: To confirm the ivermectin resistance status of a strain of Ostertagia circumcincta which was isolated from a sheep farm in the lower North Island of New Zealand and to assess the susceptibility of this strain to other macrocycliclactone anthelmintics. Twenty-five lambs housed indoors were each infected with 12,000 L3 larvae of the above parasite strain. Approximately 3 weeks after infection the lambs were allocated to 1 of 4 treatment groups (3 groups of 6, and 1 group of 7 lambs), one of which remained untreated while the others were drenched orally with ivermectin, moxidectin or abamectin at 0.2 mg/kg liveweight. Faecal egg counts (FECs) before and after treatment, and post-mortem worm burdens 10 days after treatment were examined to assess efficacies of each anthelmintic. Treatment with ivermectin reduced the mean FEC by only 18% and the mean worm burden by only 42%, whereas moxidectin and abamectin reduced FECs by 92% and worm burdens by 95%. These results, together with a similar case described recently from the South Island , confirm the emergence of ivermectin resistance in nematode parasites of sheep in New Zealand. The superior efficacy of moxidectin and abamectin in this case indicates that, following the emergence of resistance to ivermectin, some short-term practical use may still be made of these other anthelmintics. However, their continued use will undoubtedly result in increased levels of resistance and eventual therapeutic failure of these products also.
Publisher: Informa UK Limited
Date: 12-2006
DOI: 10.1080/00480169.2006.36714
Abstract: To test the hypothesis that peri-parturient anthelmintic treatment of adult ewes, either pre-lambing with a controlled- release capsule (CRC) or at tail-docking with a short-acting oral formulation, would increase the rate of development of anthelmintic resistance, as compared to not drenching ewes and giving an additional drench to lambs in the autumn. Also, to evaluate the potential of routinely leaving 15% of the heaviest lambs untreated when drenching, as a means of slowing the development of anthelmintic resistance. A replicated farmlet trial was run from 1999- 2004. Eleven farmlets, each consisting of five paddocks, were initially seeded with Ostertagia (=Teladorsagia) circumcincta and Trichostrongylus colubriformis parasites, these being a mixture of albendazole-susceptible and -resistant isolates to yield a 96% reduction in faecal nematode egg count (FEC) on drenching. Four prescriptive drenching regimes were applied Treatments 1-3 were replicated three times and Treatment 4 twice. Treatments were as follows. Treatment 1: Ewes were given an albendazole CRC pre-lambing, and any ewes exceeding 65 kg liveweight were given two capsules simultaneously lambs were given a five-drench preventive programme of treatments, orally, of albendazole on Days 0, 21, 42, 70 and 98 after weaning. Treatment 2: Ewes were given a single oral treatment of albendazole at docking (2-3 weeks after lambing), and lambs were given the same five-drench preventive programme as in Treatment 1. Treatment 3: Ewes remained untreated, while lambs were given a six-drench preventive programme of treatments, orally, of albendazole on Days 0, 21, 42, 70, 98 and 126 after weaning. Treatment 4: Ewes remained untreated, while lambs were given the same six-drench preventive programme as in Treatment 3, but the heaviest 15% of lambs were left untreated each time. Albendazole-resistance status was measured at least twice-yearly, using faecal egg count reduction tests (FECRTs) and larval development assays (LDA). In addition, controlled slaughter of drenched and undrenched tracer lambs was undertaken in the last 3 years. Resistance to albendazole increased most rapidly in Treatment 1, as measured by FECRT and LDA results, and worm burdens in tracer lambs. In Treatment 2, resistance developed slower than in Treatment 1 but faster than in Treatments 3 and 4, as measured by LDA resistance in Treatment 2 developed more quickly than in Treatment 4, as measured by FECRTs. There was no significant difference between Treatments 3 and 4, although this approached significance in Ostertagia spp, as measured by LDA. Anthelmintic treatments to adult ewes around lambing time are likely to be more selective for resistance than additional treatments administered to lambs in the autumn. Farmers wishing to slow the emergence of anthelmintic resistance on their farms should look to minimise the administration of peri-parturient treatment of ewes. A trend to slower development of resistance where a proportion of lambs were left untreated at each drench suggests further work on this aspect of management of resistance is warranted.
Publisher: Informa UK Limited
Date: 12-2006
DOI: 10.1080/00480169.2006.36713
Abstract: To provide information on current farmers' opinions and farming practices thought to be related to anthelmintic resistance, and to test for associations between the presence of anthelmintic resistance and management practices on beef-cattle rearing farms in the North Island of New Zealand. A study using an interview-based questionnaire about management of internal parasites was conducted on 62 beef cattle-rearing farms in the North Island of New Zealand, using case-control analyses to test for associations between management practices and the presence or absence of resistance to ivermectin or albendazole. Resistance was inferred from faecal nematode egg count (FEC) reduction (FECR) tests (FECRTs) when there was <90% reduction in FEC 7-10 days after treatment of calves 2 years old present mid-winter increased. It is clear that in practice anthelmintic resistance is a secondary consideration to obtaining productivity advantages from the use of anthelmintics in beef cattle. Farmers' opinions were ided on many issues and the overall impression was of confused and erse thinking regarding the principles of the use of anthelmintics. The overall outlook regarding anthelmintic resistance in cattle is bleak unless the need for integrated and long-term research activities is acted upon soon.
Publisher: Informa UK Limited
Date: 12-2006
DOI: 10.1080/00480169.2006.36712
Abstract: To identify farm practices associated with the presence of resistance to a macrocyclic lactone (ML) anthelmintic on sheep farms in New Zealand. A cross-sectional study was conducted to test for associations between the presence of resistance to an ML anthelmintic (ivermectin) and management practices on sheep farms in New Zealand. Selection of farms was both random (n=80) and purposive (n=32 being farms with a history of suspected ML resistance). Resistance was inferred from faecal nematode egg count (FEC) reduction (FECR) tests (FECRTs) when there was or =3 of the previous 5 years (odds ratio (OR) = 7.2 95% confidence interval (CI) = 1.7-30.3) on farms where 10% of the number of sheep present mid-winter (OR=7.1 95% CI=1.5-34.7) and on farms where the average wool diameter of the main flock was <37 (OR=4.1 95% CI=1.1-14.7) microns. The model provided a good fit to the data (pseudo R2=0.64 Hosmer-Lemeshow statistic = 0.38). Explanatory factors identified as associated with the presence of ML (ivermectin) resistance on farms included the use of long-acting anthelmintic formulations in ewes pre-lambing, sources of refugia of unselected parasites on the farm, breed of sheep and their requirements for anthelmintic treatments, and the importing of resistant parasites with purchased stock. The study provides support for controls that aim to provide refugia of susceptible worms and that minimise the risk of introduction of resistance through effective quarantine drenching.
Publisher: Elsevier BV
Date: 04-2019
DOI: 10.1016/J.VETPAR.2019.02.006
Abstract: Parasite control in foals is complicated by the concurrent presence of biologically erse parasites with differing levels of anthelmintic resistance. Several combination anthelmintic products are available for use in horses, but information on their efficacies against important equine parasites is scarce. Two trials were performed in New Zealand during 2008 and 2011 on four different farms with substantially different anthelmintic treatment histories. The first trial evaluated the efficacy of an ivermectin raziquantel/oxibendazole combination, a single active oxibendazole, and a single-active macrocyclic lactone (ML) in 49 foals located on three farms. The second trial evaluated two combination anthelmintic products and three single-active ML products and enrolled a total of 110 foals on three farms. Foals in the second trial were allocated to one of six anthelmintic treatment groups oxfendazole yrantel embonate, pyrantel embonate/ivermectin raziquantel, ivermectin raziquantel, abamectin raziquantel, moxidectin raziquantel, and a placebo-treated control. In both trials, foals were monitored monthly prior to treatment, and fecal egg counts (FECs) of Parascaris spp., strongylid, and Strongyloides westeri were determined. A "rolling enrolment" process was implemented whereby foals were systematically allocated to a treatment group and treated with the corresponding anthelmintic following the first appearance of Parascaris spp. eggs in the faeces. A generalised linear model was used to evaluate the effect of farm and treatment on Day14 FEC (ln) for each parasite. Three different FECR calculation methods were employed as follows i) FECR(T) pre and post treatment ii) FECR (C) in the treated group compared with control, and iii) FECR (P) pre- and post- treatment in the treated and control groups. Across both trials, treatment with ML single active products failed to achieve >95% reduction in Parascaris spp. FEC on two of three farms. The pyrantel embonate/oxfendazole and ivermectin/ praziquantel/oxibendazole combinations demonstrated full efficacy against Parascaris spp. This is in contrast to the anti-strongylid efficacies determined, where the pyrantel embonate/oxfendazole combination and single active oxibendazole had reduced efficacy on one farm, while the macrocyclic lactones generally had good efficacy. Strongyloides egg counts were sporadic in both trials, and allowed limited insight into anthelmintic efficacy. The study illustrated the importance of keeping an untreated or placebo-treated control group in studies evaluating anti-Parascaris efficacy and it demonstrated the utility of a rolling enrolment procedure, where foals are enrolled over the course of a defined period of time. Furthermore, the study demonstrated the value of a farm specific FECR monitoring programme and the complexity of parasite control in foals, where combination anthelmintic products can be employed to target multiple species of parasites.
Publisher: Informa UK Limited
Date: 10-2004
Publisher: Informa UK Limited
Date: 04-2002
DOI: 10.1080/00480169.2002.36253
Abstract: To determine whether: a) using a controlled-release anthelmintic capsule (CRC) instead of a programme of 5 oral drenches administered at 3-4 week intervals, would delay the development of anti-parasite immunity in lambs b) the use of ivermectin instead of albendazole, administered either as a CRC or as a programme of 5 oral drenches, would delay the development of anti-parasite immunity in lambs c) lambs treated with CRCs would have higher liveweight gains than lambs drenched orally 5 times at 3-4 week intervals, and d) delayed onset of anti-parasite immunity is associated with reduced liveweight gains in the period following anthelmintic treatment. Three field trials were conducted, 1 on a research farm and 2 on commercial sheep farms, in which groups of 30 lambs were treated with either a CRC containing albendazole, a CRC containing ivermectin, 5 oral drenches with albendazole, or 5 oral drenches with ivermectin, administered at 3-4 week intervals. Liveweights and faecal nematode egg counts (FECs) were recorded in all trials. Immunoglobulin-G (IgG) antibody levels to Ostertagia circumcincta and Trichostrongylus colubriformis adult and larval antigens were measured in Trials 1 and 3, and fleece weights and resistance of animals to nematode challenge infection were measured in Trial 1. CRC-treated lambs had higher levels of antibodies to O. circumcincta infective-stage larvae (L3) than orally drenched lambs in Trial 3, but no other immunological differences due to mechanism of delivery were detected. Antibody levels were lower in lambs treated with ivermectin than albendazole, as a CRC or oral drench in Trial 1, but this was not associated with any measurable effects on FEC or productivity. No significant differences (p>0.05) were detected between drench types (albendazole vs ivermectin) or delivery mechanisms (CRC vs oral drenching) in any of the production parameters measured, in any of the trials. Albendazole-CRCs failed to control FECs in all 3 trials. Although some differences between treatments in antibody levels were detected these were not associated with measurable differences in level of parasitism or productivity of lambs. CRC use did not appear to offer substantial gains in productivity over a structured programme of 5 oral drenches administered at 3-4 week intervals.
Publisher: Elsevier BV
Date: 10-2002
DOI: 10.1016/S0304-4017(02)00247-9
Abstract: Eighty-eight lambs were allocated to one of four groups which were then dosed with 10,000 infective-stage larvae (L3) of one of four populations of Ostertagia circumcincta the first (S) was an isolate known to be anthelmintic-susceptible the second (OR) was a multiple anthelmintic-resistant isolate which had been recovered from the field following therapeutic failure of both ivermectin and moxidectin and subsequently maintained in the laboratory without further anthelmintic selection. The third (R) was derived from OR but had been passaged for five generations in the laboratory with each generation being screened with all three broad-spectrum drench families the fourth (R x S) was an F1 cross between the S and R isolates. On patency, each of the four infection groups was sub- ided into five treatment groups, one of which received no anthelmintic while the others were administered either oral ivermectin (IVM-oral), controlled-release capsules containing ivermectin (IVM-CRCs), oral moxidectin (MOX-oral) or injectable MOX (MOX-inj). Neither formulation of IVM reduced FEC in the R, R x S and OR infected lambs compared to their untreated controls, but significant reductions were observed in all cases following MOX-oral or MOX-inj treatment. Similarly, neither IVM formulation significantly reduced the numbers of R or R x S worms compared to their untreated controls, although the numbers of OR worms were reduced in both cases (P<0.05). Direct comparisons of efficacy across the isolates, however, indicated that neither formulation was any more effective against R x S or OR worms than against the more highly selected R worms. In contrast, both MOX formulations significantly reduced worm numbers of all the resistant isolates compared to their respective untreated controls furthermore, worm burdens of R x S were reduced significantly more than burdens of R (P<0.05). Reductions in OR burdens, which were intermediate between the two, did not differ significantly from either. The results are consistent with published work on Haemonchus contortus, which suggests that macrocyclic lactone (ML) resistance is expressed as a dominant trait under treatment with IVM. However, these data differ from the H. contortus studies in suggesting that ML resistance in O. circumcincta may effectively be rendered incompletely dominant or recessive by treatment with MOX.
Publisher: Cambridge University Press (CUP)
Date: 08-2000
DOI: 10.1017/S0031182099006204
Abstract: Five groups of ten 7-month-old Romney lambs were challenged twice-weekly (2 x 3,000) with either Ostertagia circumcincta (Groups 1-3) or Trichostrongylus colubrifornzis (Groups 4 and 5) infective-stage larvae (L3) following administration of controlled release capsules (CRC) containing either albendazole (ABZ-CRC) (Groups 2 and 5) or ivermectin (IVM-CRC) (Group 3). Larval challenge comprised a mixture of equal numbers of drug-susceptible and -resistant L3 (OR/TR:OS/TS) during the 14-week period of drug release. Positive faecal egg counts (FEC) were recorded in each group during this period. Eggs recovered from faeces were used in an egg hatch assay (EHA) utilizing different concentrations of ABZ. O. circumcincta eggs from Groups 2 and 3 had significantly higher LC50 values than Group 1 eggs of T. colubriformis from the ABZ-CRC treated Group 5 had a higher LC50 than control Group 4. Following the exhaustion of drug release, larval challenge was changed to consist of only susceptible parasites and EHA performed wveekly to determine whether LC50 declined, which would indicate dilution or replacement of drench survivors. In those animals challenged with O. circumcincta, LC50 values were still significantly higher in Groups 2 and 3 at week 19 than in the previously untreated Group 1. For T. colubriformis, LC50 values declined steadily following exhaustion of drug release and were not significantly different between Groups 4 and 5 by week 20. This decline in LC50, and corresponding rise in FEC, was largely the result of 3 animals which dominated with high FEC. The remaining 6 animals showed little decline in LC50 or rise in FEC. The results demonstrate the ability of persistent drugs to screen for resistant parasites and establish that the period of selective advantage for drug-resistant parasites of both species is significantly longer than the period of drug release from CRCs.
Publisher: Informa UK Limited
Date: 04-2008
DOI: 10.1080/00480169.2008.36810
Abstract: To confirm the presence of multiple anthelmintic resistance on a sheep farm in New Zealand. Three groups of 10 weaned Romney-cross lambs were treated either with an oral dose of ivermectin (0.2 mg/kg), or a benzimidazole/levamisole (BZ/LEV) combination (4.75 albendazole and 7.5 mg/kg levamisole), or were left untreated. Ten days later, animals were necropsied, and adult worms recovered and identified from the abomasa and small intestines. Pre- and post-treatment faecal nematode egg counts (FEC) were recorded, and larval cultures were performed. In a faecal egg count reduction test (FECRT), adjusted to reflect pre- and post-treatment larval culture results, ivermectin resistance was detected in Teladorsagia (Ostertagia), Trichostrongylus and Haemonchus spp, while BZ/LEV combination- resistant Teladorsagia and Trichostrongylus spp were also present. Adult worm counts confirmed these results, and identified the species involved as Teladorsagia circumcincta, Trichostrongylus colubriformis and H. contortus. Multiple, multi-generic anthelmintic resistance was confirmed on a sheep property in New Zealand. This included the first confirmed case of ivermectin resistance in T. colubriformis from sheep in New Zealand.
Publisher: Springer Science and Business Media LLC
Date: 1998
Abstract: Groups of lambs either with or without controlled-release albendazole (ABZ) capsules (CRCs) were challenged twice weekly for 6 weeks with either drug-susceptible or drug-resistant Ostertagia circumcincta and Trichostrongylus colubriformis. Groups with and without CRCs remained unchallenged as controls. There was minimal establishment of drug-susceptible parasites of either species in those lambs with CRCs. However, drug-resistant parasites of both species established adult worm burdens in the presence of the capsules. The humoral immune response, as measured by the serum antilarval (L3) antibody (Ab) titre, was pooled for weeks 4-6 and compared for each group. With the exception of anti-T. colubriformis Ab in group 2, anti-L3 Ab titres were significantly higher in all the parasite-challenged groups as compared to the control animals. Also, with the exception of anti-resistant O. circumcincta Ab levels in the CRC-treated animals (group 5), no significant difference was observed in Ab titres between the four groups challenged with either resistant or susceptible larvae. The results demonstrate the inability of CRCs to prevent establishment of drug-resistant parasites and that immune stimulation is not inhibited by the capsules.
Publisher: Elsevier BV
Date: 1999
DOI: 10.1016/S0304-4017(98)00220-9
Abstract: The effect of albendazole (ABZ)-capsule (CRC) administration on parasite establishment and immunity to ABZ-resistant (RES) and -susceptible (SUS) T. colubriformis was measured in Romney lambs. During 12 weeks of twice-weekly dosing with 3000 parasite larvae (L3), eggs were observed in faeces from CRC-treated and untreated lambs given RES L3, but not CRC-treated lambs given SUS L3. Following the period of trickle challenge all lambs were drenched and, 1 week later, dosed with 20000 SUS L3. Resulting worm burdens were higher in control lambs than in those previously treated with CRCs and challenged with SUS, which in turn were higher than those in the CRC-treated or -untreated lambs previously challenged with RES L3. During the period of trickle challenge, the number of peripheral eosinophils and titres of anti-L3 and anti-adult antibody were raised only in those groups given RES L3. There was no effect of CRC administration. Following drench and challenge, antibody titres and eosinophil numbers increased in the control animals but not in those groups which had received previous trickle infection. The results demonstrate that the larval challenge alone resulted in incomplete though substantial protection against subsequent parasite challenge. The use of CRCs may potentially impact on subsequent animal performance and selection for anthelmintic resistance through a reduced level of immunity.
Publisher: Informa UK Limited
Date: 22-02-2016
DOI: 10.1080/00480169.2016.1149117
Abstract: To determine the prevalence of benzimidazole resistance in Nematodirus spathiger and N. filicollis from a s le of New Zealand farms. The efficacy of albendazole (ABZ) against Nematodirus spp. was assessed by faecal nematode egg count reduction (FECR) tests undertaken in lambs aged 3-8 months old on 27 sheep farms throughout New Zealand. On each farm, groups of 10-16 lambs were either treated with ABZ (4.75 mg/kg) or remained as untreated controls. Faecal s les were collected from all animals at the time of treatment and 7-10 days later. Faecal nematode egg counts (FEC) were performed using a modified McMaster technique. Larvae were cultured from pooled faecal s les, collected 7-10 days after treatment from each group, by incubation at 20°C for 6 weeks, 4°C for 26 weeks then 13°C for 2 weeks. The resulting third stage larvae were identified to species using a multiplex PCR assay, that identified species-specific sequences in the second internal transcribed spacer region of ribosomal DNA. The efficacy of ABZ for N. spathiger and N. filicollis was calculated from the proportion of the two species in culture and the group mean FEC before and after treatment. Only farms with a mean of 10 epg for each species in untreated s les were included for analysis. Resistance was defined as an efficacy <95%. On farms that met the threshold of 10 epg in faecal s les, benzimidazole resistance was found on 20/21 (95%) farms for N. spathiger compared with 4/10 (40%) farms for N. filicollis (p<0.05). In s les collected following treatment, a mean of 83 (min 46, max 100)% of Nematodirus spp. larvae recovered from the untreated groups were N. spathiger, compared with 94 (min 45, max 100)% in the ABZ treated groups (p=0.03). This change in percentage was not influenced by the overall efficacy of treatment based on the FECR test (p=0.324). The results confirm the high level of resistance in N. spathiger in New Zealand and that benzimidazole resistance was more common in N. spathiger than N. filicollis. While resistance to benzimidazole anthelmintics has been reported previously in New Zealand, this is the first report of N. filicollis being resistant to benzimidazole anthelmintics.
No related grants have been discovered for Dave Leathwick.