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Sustainable control of worms in sheep

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Sustainable control of worms in sheep

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    1. Sustainable control of worms in sheep

    2. Sustainable worm control in sheep

    3. Sustainable worm control in sheep

    4. Sustainable worm control in sheep NSA (Chair) SNFU Defra SAC NOAH AHDA RUMA CSL RVC SVS More information about SCOPS is available on the NSA website - see the last slide.More information about SCOPS is available on the NSA website - see the last slide.

    5. Sustainable worm control in sheep The SCOPS terms of reference are : To advise and disseminate new recommendations on sustainable parasite control to the sheep industry, initially concentrating on internal parasites To provide a forum for feedback from the sheep and animal health industries, veterinary profession and allied groups To consider new developments, feedback and information and revise the recommendations accordingly To facilitate mechanisms to inform all stakeholders in the sheep industry. Ensure that the messages have consistency and clarity. SCOPS is represented by a steering committee, with the objective of improving the way in which sheep parasites are managed, and providing a mechanism by which guidelines are prepared, presented to industry, reviewed in the light of experience, feedback from industry and new research, and amended and developed as necessary. SCOPS is represented by a steering committee, with the objective of improving the way in which sheep parasites are managed, and providing a mechanism by which guidelines are prepared, presented to industry, reviewed in the light of experience, feedback from industry and new research, and amended and developed as necessary.

    6. Introduction Over the past 20-30 years : dependence on anthelmintic use has increased anthelmintic resistance has emerged as a problem worldwide and, latterly, in the UK parasite epidemiology has changed there is new understanding of AR and its control some of the strategies which have been recommended for worm control select for AR See Section 1.1 of the text, Sustainable Worm Control in Sheep. See Section 1.1 of the text, Sustainable Worm Control in Sheep.

    7. Since the introduction of the CAP Sheepmeat Regime in 1980, there has been a huge increase in sheep numbers in the UK, in particular in lowland and upland areas. During the same period, however, the number of cattle and the area of temporary grassland have both declined by 25%. In the lowlands, EU support for arable farming since 1991 has meant that sheep have been pushed almost exclusively onto areas of permanent grassland, where a mono-culture of sheep production prevails. The net effect is that the opportunities for the alternation of sheep, cattle and conservation, and/or the use of new leys, as a means of reducing worm burdens have been significantly reduced. As a result, sheep farmers have become increasingly reliant on the routine use of anthelmintics in worm control programmes. See Section 1.2 of the text, Sustainable Worm Control in Sheep. Since the introduction of the CAP Sheepmeat Regime in 1980, there has been a huge increase in sheep numbers in the UK, in particular in lowland and upland areas. During the same period, however, the number of cattle and the area of temporary grassland have both declined by 25%. In the lowlands, EU support for arable farming since 1991 has meant that sheep have been pushed almost exclusively onto areas of permanent grassland, where a mono-culture of sheep production prevails. The net effect is that the opportunities for the alternation of sheep, cattle and conservation, and/or the use of new leys, as a means of reducing worm burdens have been significantly reduced. As a result, sheep farmers have become increasingly reliant on the routine use of anthelmintics in worm control programmes. See Section 1.2 of the text, Sustainable Worm Control in Sheep.

    8. The prevalence of resistance to the benzimidazole (BZ) group has increased dramatically between 1991 and 2000 and is now quite high in the UK. See Section 1.4 of the text, Sustainable Worm Control in Sheep. The prevalence of resistance to the benzimidazole (BZ) group has increased dramatically between 1991 and 2000 and is now quite high in the UK. See Section 1.4 of the text, Sustainable Worm Control in Sheep.

    9. The parasites The major worm parasites of sheep in the UK include Gastrointestinal nematodes The trematode Fasciola hepatica The lung worms

    10. The parasites This presentation is concerned with the gastrointestinal nematodes, and not the lungworms, and brief mention is made of Fasciola hepatica.

    11. Anthelmintics Broad-spectrum anthelmintics fall into three main classes: BZ benzimidazoles LM levamisole and morantel ML macrocyclic lactones As side-resistance to anthelmintics occurs within these classes, effectively there are only three ‘different’ types of broad-spectrum anthelmintics available. There are also narrow spectrum drugs available, like closantel against Haemonchus (and fluke), nitroxynil against fluke (and Haemonchus) and triclabendazole against fluke.As side-resistance to anthelmintics occurs within these classes, effectively there are only three ‘different’ types of broad-spectrum anthelmintics available. There are also narrow spectrum drugs available, like closantel against Haemonchus (and fluke), nitroxynil against fluke (and Haemonchus) and triclabendazole against fluke.

    12. What is anthelmintic resistance (AR)? the parasite can tolerate anthelmintic doses which are normally lethal the ability to do so is heritable Resistance is the heritable ability of the parasite to tolerate a normally effective dose of the anthelmintic. The parasite is considered resistant if it survives exposure to the standard recommended dose of the anthelmintic and the ability to survive is passed on to its offspring. Resistance is best viewed as drug tolerance, since ‘resistant’ individuals can often be removed by exposure to higher dose rates of anthelmintic up to the maximum tolerated dose. See Section 5.1 of the text, Sustainable Worm Control in Sheep. Resistance is the heritable ability of the parasite to tolerate a normally effective dose of the anthelmintic. The parasite is considered resistant if it survives exposure to the standard recommended dose of the anthelmintic and the ability to survive is passed on to its offspring. Resistance is best viewed as drug tolerance, since ‘resistant’ individuals can often be removed by exposure to higher dose rates of anthelmintic up to the maximum tolerated dose. See Section 5.1 of the text, Sustainable Worm Control in Sheep.

    13. How is resistance measured? faecal egg count reduction trials (FECRT) resistance is declared if dosing does not reduce FEC by at least 95% anthelmintics may ‘appear’ to be still working even if reduction in FEC is only 60% to 80% resistance is also measured in laboratory-based larval development assays We measure degrees of anthelmintic resistance in a number of ways including field tests like faecal egg count reduction trials (FECRTs) and laboratory assays, like the larval development test (LDT). In FECRTs we expect an effective anthelmintic to reduce egg counts by 100%, ie, to zero. When measured this way, resistance is said to exist if the reduction in egg count is less than 95%. Anthelmintics will continue to give clinical responses in parasitised sheep even if the reduction in faecal egg count (FEC) is substantially less than 95%. Consequently, sheep farmers may not be aware that resistance to an anthelmintic is present if they are still achieving 80%-90% reduction in FEC. At this level, however, significant production penalties from poor worm control may be incurred and, additionally, resistance is expected to become more severe quite rapidly if the anthelmintic remains in use. See Section 5.1 of the text, Sustainable Worm Control in Sheep. We measure degrees of anthelmintic resistance in a number of ways including field tests like faecal egg count reduction trials (FECRTs) and laboratory assays, like the larval development test (LDT). In FECRTs we expect an effective anthelmintic to reduce egg counts by 100%, ie, to zero. When measured this way, resistance is said to exist if the reduction in egg count is less than 95%.

    14. How does resistance appear? resistance alleles pre-exist in most worm populations even before anthelmintics are ever used then, when the anthelmintic is used, the very few worms with resistance alleles are favoured resistance develops slowly at first, then more rapidly as allele frequency increases The genes, or alleles, which allow parasites to be resistant to anthelmintics are believed to be in existence in unselected worm populations. Consequently, for all anthelmintics that have been invented to date, it appears that the development of AR is an inevitable consequence of their use, but its development can be delayed. See Section 5.4 of the text, Sustainable Worm Control in Sheep. The genes, or alleles, which allow parasites to be resistant to anthelmintics are believed to be in existence in unselected worm populations. Consequently, for all anthelmintics that have been invented to date, it appears that the development of AR is an inevitable consequence of their use, but its development can be delayed. See Section 5.4 of the text, Sustainable Worm Control in Sheep.

    15. This is a theoretical representation of the rate at which anthelmintic resistance might develop in a worm population. Two assumptions are (1) that selection pressure is constant (ie, the same anthelmintic remains in use) and (2), resistance is conferred by two recessive alleles, so only homozygous-resistant parasites survive treatment.. The figure shows that (a) resistance develops slowly at first then more quickly as the frequency of resistance alleles exceeds 5% to 10% of all alleles, and (b) the frequency of homozygous resistant worms lags behind the frequency of resistance alleles.This is a theoretical representation of the rate at which anthelmintic resistance might develop in a worm population. Two assumptions are (1) that selection pressure is constant (ie, the same anthelmintic remains in use) and (2), resistance is conferred by two recessive alleles, so only homozygous-resistant parasites survive treatment.. The figure shows that (a) resistance develops slowly at first then more quickly as the frequency of resistance alleles exceeds 5% to 10% of all alleles, and (b) the frequency of homozygous resistant worms lags behind the frequency of resistance alleles.

    16. By the time resistance is detectable in a worm population using a faecal egg count reduction trial, or a larval development assay, the frequency of resistance alleles in the population is already quite high (point B).By the time resistance is detectable in a worm population using a faecal egg count reduction trial, or a larval development assay, the frequency of resistance alleles in the population is already quite high (point B).

    17. Unless tests are carried out, sheep farmers will continue to see clinical responses to anthelmintics until the drug is killing fewer than 30% to 40% of the worms (point C). By this time probably something like half of the alleles in the population are for resistance alleles.Unless tests are carried out, sheep farmers will continue to see clinical responses to anthelmintics until the drug is killing fewer than 30% to 40% of the worms (point C). By this time probably something like half of the alleles in the population are for resistance alleles.

    18. Will resistance go away if the farmer stops using the anthelmintic? the short answer is ‘No!’ once resistance to an anthelmintic emerges, reversion to susceptibility is unlikely to occur The genes, or alleles, which allow parasites to be resistant to anthelmintics are believed to be in existence in unselected worm populations. Consequently, for all anthelmintics that have been invented to date, it appears that the development of AR is an inevitable consequence of their use, but its development can be delayed. See Section 5.4 of the text, Sustainable Worm Control in Sheep. The genes, or alleles, which allow parasites to be resistant to anthelmintics are believed to be in existence in unselected worm populations. Consequently, for all anthelmintics that have been invented to date, it appears that the development of AR is an inevitable consequence of their use, but its development can be delayed. See Section 5.4 of the text, Sustainable Worm Control in Sheep.

    19. Resistant alleles make worms less fit to survive in the absence of anthelmintic So, in theory, reversion to susceptibility should occur when the anthelmintic is not used Possibly, this happens in zone A It appears, however, that once AR is in zone B, co-adaptation to survival means that resistant parasites are equally fit for survival as susceptible ones. Reversion to susceptibility Once the frequency of resistance alleles is detectable (point B onwards), cessation of use of the anthelmintic is very unlikely to lead to a reversion to susceptibility. Instead, the frequency of resistance alleles is predicted to remain more or less static, and will start to increase again if the anthelmintic is used again. If reversion is ever likely to occur, it will be at point A or earlier - well before AR is detectable with currently-available tests. See Sections 5.1, 5.5 and 5.9 of the text, Sustainable Worm Control in Sheep.Once the frequency of resistance alleles is detectable (point B onwards), cessation of use of the anthelmintic is very unlikely to lead to a reversion to susceptibility. Instead, the frequency of resistance alleles is predicted to remain more or less static, and will start to increase again if the anthelmintic is used again. If reversion is ever likely to occur, it will be at point A or earlier - well before AR is detectable with currently-available tests. See Sections 5.1, 5.5 and 5.9 of the text, Sustainable Worm Control in Sheep.

    20. What factors influence the rate of AR development? The relative size of the in-refugia population. Frequency of treatment Rate of re-infection after dosing Dose rates The next two slides describe what is meant by ‘in-refugia’The next two slides describe what is meant by ‘in-refugia’

    21. In any parasite ecosystem, there are two sub-populations of worms; the parasitic and the free-living. It is only the parasitic sub-population (the parasites within the host) that is exposed to any anthelmintic treatment. See Sections 5.4.2 of the text, Sustainable Worm Control in Sheep. In any parasite ecosystem, there are two sub-populations of worms; the parasitic and the free-living. It is only the parasitic sub-population (the parasites within the host) that is exposed to any anthelmintic treatment. See Sections 5.4.2 of the text, Sustainable Worm Control in Sheep.

    22. Worms that are in the free-living sub-population (eggs, L1, L2, L3) are not exposed to the anthelmintic and are said to be in refugia. Any worms in sheep that are not treated also contribute to the in refugia sub-population. One of the important factors influencing the rate at which resistance develops in a worm population is the relative size of the exposed population and the unexposed or in refugia population. In general, the larger the in refugia population in comparison to the exposed population, the more slowly resistance will develop. See Sections 5.4.2 of the text, Sustainable Worm Control in Sheep. Worms that are in the free-living sub-population (eggs, L1, L2, L3) are not exposed to the anthelmintic and are said to be in refugia. Any worms in sheep that are not treated also contribute to the in refugia sub-population. One of the important factors influencing the rate at which resistance develops in a worm population is the relative size of the exposed population and the unexposed or in refugia population. In general, the larger the in refugia population in comparison to the exposed population, the more slowly resistance will develop. See Sections 5.4.2 of the text, Sustainable Worm Control in Sheep.

    23. Factors influencing the rate of AR development 1. The relative size of the in-refugia population The larger the in-refugia population, relative to the exposed population, the slower AR will develop. When an entire group of sheep is treated prior to a move to a low-contamination pasture, the in-refugia population is relatively small. A low contamination pasture has, by definition, a small population in refugia. When the whole group is treated, only resistant parasites survive treatment and produce eggs on the low-contamination pasture. There are relatively few free-living stages to dilute the eggs from resistant parasites, so the frequency of resistant phenotypes in the free-living population may change substantially faster than would occur if the pasture had been more contaminated.A low contamination pasture has, by definition, a small population in refugia. When the whole group is treated, only resistant parasites survive treatment and produce eggs on the low-contamination pasture. There are relatively few free-living stages to dilute the eggs from resistant parasites, so the frequency of resistant phenotypes in the free-living population may change substantially faster than would occur if the pasture had been more contaminated.

    24. What factors influence the rate of AR development? The relative size of the in-refugia population. Frequency of treatment Rate of re-infection after dosing Dose rates The next slide describes the importance of treatment frequency in AR development. See Sections 5.4.3 of the text, Sustainable Worm Control in SheepThe next slide describes the importance of treatment frequency in AR development. See Sections 5.4.3 of the text, Sustainable Worm Control in Sheep

    25. Factors influencing the rate of AR development 2. Frequency of treatment More frequent treatment selects faster for AR Treatment is particularly selective when frequency approaches the pre-patent period Treatment gives the resistant worms a reproductive advantage over susceptible worms The more frequently treatment is given, the faster AR develops. The underlying principle of selection for AR is that treatment gives the resistant worms a reproductive advantage over the susceptible worms. For two to three weeks or so after dosing, before newly ingested L3 have become egg-laying adults, the only eggs being passed in the faeces of dosed sheep are from worms which survived treatment. When the interval between dosing becomes shorter, and approaches the pre-patent period of the worm, the susceptible worms have less and less opportunity to produce eggs and most, or all, pasture contamination occurs with eggs from resistant parasites. If this strategy is continued the susceptible population is progressively replaced with a resistant one. The more frequently treatment is given, the faster AR develops. The underlying principle of selection for AR is that treatment gives the resistant worms a reproductive advantage over the susceptible worms. For two to three weeks or so after dosing, before newly ingested L3 have become egg-laying adults, the only eggs being passed in the faeces of dosed sheep are from worms which survived treatment. When the interval between dosing becomes shorter, and approaches the pre-patent period of the worm, the susceptible worms have less and less opportunity to produce eggs and most, or all, pasture contamination occurs with eggs from resistant parasites. If this strategy is continued the susceptible population is progressively replaced with a resistant one.

    26. What factors influence the rate of AR development? The relative size of the in-refugia population. Frequency of treatment Rate of re-infection after dosing Dose rates The concept of re-infection rate after dosing is important in understanding the importance of the immune ewe in contributing to the development of AR. The next slide, and the ‘more information’ slide expand on the issue. See Sections 5.4.4 of the text, Sustainable Worm Control in SheepThe concept of re-infection rate after dosing is important in understanding the importance of the immune ewe in contributing to the development of AR. The next slide, and the ‘more information’ slide expand on the issue. See Sections 5.4.4 of the text, Sustainable Worm Control in Sheep

    27. Factors influencing the rate of AR development 3. Rate of re-infection after dosing After dosing, resistant parasites have a period of reproductive advantage The period is shorter if the sheep become quickly re-infected. If re-infection is delayed, resistant survivors have the advantage for longer. After dosing, resistant parasites in the sheep enjoy a period of reproductive advantage over the susceptible parasites, the extent of which depends on how quickly the sheep become re-infected with L3 from the unselected population on pasture. If the pasture is highly infective, and the sheep are highly susceptible, re-infection occurs quickly and selection for resistance is minimised. An adult worm burden derived from the unselected population of larvae in refugia is re-established within 3-4 weeks. After dosing, resistant parasites in the sheep enjoy a period of reproductive advantage over the susceptible parasites, the extent of which depends on how quickly the sheep become re-infected with L3 from the unselected population on pasture. If the pasture is highly infective, and the sheep are highly susceptible, re-infection occurs quickly and selection for resistance is minimised. An adult worm burden derived from the unselected population of larvae in refugia is re-established within 3-4 weeks.

    28. Rapid re-infection after dosing The factors which influence re-infection rates after dosing are the infectivity of the pasture the susceptibility of the sheep lambs >> ewes Dosing of immune ewes may be a significant factor selecting for AR If re-infection is delayed, the resistant survivors will enjoy a longer period of reproductive advantage. Re-infection could be delayed if the pasture is of low contamination, if climatic conditions do not favour the movement of L3 onto pasture (too dry, for example), if the sheep has a relatively strong acquired resistance or if the sheep have been treated with a persistent anthelmintic. Lambs are more susceptible than ewes, so become re-infected faster. Ewes during the PPRI, however, are relatively susceptible for a few weeks but regain their immunity a few weeeks into lactation. In New Zealand, it is believed that the anthelmintic treatment of ewes that display strong immunity, or regain strong immunity soon after anthelmintic treatment, has contributed significantly to the development of AR. If re-infection is delayed, the resistant survivors will enjoy a longer period of reproductive advantage. Re-infection could be delayed if the pasture is of low contamination, if climatic conditions do not favour the movement of L3 onto pasture (too dry, for example), if the sheep has a relatively strong acquired resistance or if the sheep have been treated with a persistent anthelmintic. Lambs are more susceptible than ewes, so become re-infected faster. Ewes during the PPRI, however, are relatively susceptible for a few weeks but regain their immunity a few weeeks into lactation. In New Zealand, it is believed that the anthelmintic treatment of ewes that display strong immunity, or regain strong immunity soon after anthelmintic treatment, has contributed significantly to the development of AR.

    29. What factors influence the rate of AR development? The relative size of the in-refugia population. Frequency of treatment Rate of re-infection after dosing Dose rates In the past, under-dosing of sheep with anthelmintics was probably common-place, because either the weight of the sheep was under-estimated, instructions for dose calculation were misleading or dosing equipment was faulty. This is now recognised as a very significant factor in the development of resistance to BZ and LM anthelmintics particularly. The reasons why dose rates are important are expanded in the following slide. See Sections 5.4.5 of the text, Sustainable Worm Control in Sheep In the past, under-dosing of sheep with anthelmintics was probably common-place, because either the weight of the sheep was under-estimated, instructions for dose calculation were misleading or dosing equipment was faulty. This is now recognised as a very significant factor in the development of resistance to BZ and LM anthelmintics particularly. The reasons why dose rates are important are expanded in the following slide. See Sections 5.4.5 of the text, Sustainable Worm Control in Sheep

    30. Factors influencing the rate of AR development 4. Dose rates Under-dosing encouraged the rapid appearance of AR to the BZ and LM anthelmintics Under-dosing allows heterozygous parasites to survive Full doses should kill all but homozygous-resistant parasites Resistance to BZ and LM anthelmintics appears to be a trait regulated by a recessive gene. Full doses, therefore, kill heterozygous parasites as well as homozygous-susceptibles. Under-dosing, by allowing heterozygous parasites to survive effectively make the gene dominant. Resistance to the MLs appears to be regulated by a dominant gene, so the model described in the slide does not apply so well to ML resistance.Resistance to BZ and LM anthelmintics appears to be a trait regulated by a recessive gene. Full doses, therefore, kill heterozygous parasites as well as homozygous-susceptibles. Under-dosing, by allowing heterozygous parasites to survive effectively make the gene dominant. Resistance to the MLs appears to be regulated by a dominant gene, so the model described in the slide does not apply so well to ML resistance.

    31. What can be done to delay AR? Rotations of anthelmintics Combinations of anthelmintics Prevent the entry of resistant worms onto farms from other farms. Rotations between anthelmintic classes may reduce the rate at which AR develops but the evidence supporting the hypothesis is not strong. If it does help, it is likely to do so only in the very early stages of AR development (zone A in slide 14). On many farms, ML resistance may be in zone A, so rotations may be useful in that instance. See Sections 5.6 of the text, Sustainable Worm Control in Sheep Rotations between anthelmintic classes may reduce the rate at which AR develops but the evidence supporting the hypothesis is not strong. If it does help, it is likely to do so only in the very early stages of AR development (zone A in slide 14). On many farms, ML resistance may be in zone A, so rotations may be useful in that instance. See Sections 5.6 of the text, Sustainable Worm Control in Sheep

    32. What can be done to delay AR? Rotations of anthelmintics Combinations of anthelmintics Prevent the entry of resistant worms onto farms from other farms. Combinations of broad-spectrum anthelmintics are useful to delay the development of AR, particularly in the very early stages (zone A) of AR development. In this context, the application of broad-spectrum combinations, targetting the same parasite species should be differentiated from the use of combinations of narrow-spectrum and broad-spectrum anthelmintics targetting more than one species. These latter combinations (eg, flukicide plus broad-spectrum) are discouraged unless there is a clear case for their use because of inadvertent selection pressure for AR in non-target parasites. See Sections 5.7 of the text, Sustainable Worm Control in Sheep Combinations of broad-spectrum anthelmintics are useful to delay the development of AR, particularly in the very early stages (zone A) of AR development. In this context, the application of broad-spectrum combinations, targetting the same parasite species should be differentiated from the use of combinations of narrow-spectrum and broad-spectrum anthelmintics targetting more than one species. These latter combinations (eg, flukicide plus broad-spectrum) are discouraged unless there is a clear case for their use because of inadvertent selection pressure for AR in non-target parasites. See Sections 5.7 of the text, Sustainable Worm Control in Sheep

    33. What can be done to delay AR? Rotations of anthelmintics Combinations of anthelmintics Prevent the entry of resistant worms onto farms from other farms. Resistance can delelop on a farm as a result of selection practised within the resident worm population or through the importation of a significant population of resistant worms onto the farm, from another flock where AR is a serious problem. See Sections 5.8 of the text, Sustainable Worm Control in Sheep Resistance can delelop on a farm as a result of selection practised within the resident worm population or through the importation of a significant population of resistant worms onto the farm, from another flock where AR is a serious problem. See Sections 5.8 of the text, Sustainable Worm Control in Sheep

    34. The new guidelines An 8 step strategy Many of the recommended steps are unchanged from previous guidelines There are some key new recommendations, as a result of research and experience in UK and other countries Importance of involving expert advice is emphasised See Section 6 of the text, Sustainable Worm Control in Sheep. See Section 6 of the text, Sustainable Worm Control in Sheep.

    35. Work out a control strategy with your veterinarian or advisor. Use effective quarantine strategies to prevent the importation of resistant worms in introduced sheep and goats Test for AR on your farm Administer anthelmintics effectively Use anthelmintics only when necessary Select the appropriate anthelmintic for the task Adopt strategies to preserve susceptible worms on the farm Reduce dependence on anthelmintics These are the eight key messages being propagated to sheep farmers. |note that consultation with a veterinarian is number one. Each of these messages will be described in detail in the following slides. These are the eight key messages being propagated to sheep farmers. |note that consultation with a veterinarian is number one. Each of these messages will be described in detail in the following slides.

    36. 1. Work out a control strategy with your veterinarian or advisor. The need for specialist consultation is greater now than before. Decisions about judicious use of anthelmintics in worm control programs are complex, and will require on-going consultations On-going consultations between farmers, their veterinarians and advisors will be needed to combine an expert knowledge of worm parasites with a practical and detailed understanding of the individual farm and its sheep flock. This relationship needs to evolve, so that the farmer bases tactical decisions within the context of an agreed strategy. This will need to be updated by advice and interpretation of analyses, such as FECs, which give up to date information on the status of the flock See Section 6.1 of the text, Sustainable Worm Control in Sheep. On-going consultations between farmers, their veterinarians and advisors will be needed to combine an expert knowledge of worm parasites with a practical and detailed understanding of the individual farm and its sheep flock. This relationship needs to evolve, so that the farmer bases tactical decisions within the context of an agreed strategy. This will need to be updated by advice and interpretation of analyses, such as FECs, which give up to date information on the status of the flock See Section 6.1 of the text, Sustainable Worm Control in Sheep.

    37. 2. Use effective quarantine strategies Introduction of resistance alleles is considered a major cause of AR in UK flocks. The recommended strategy involves three steps: The objective of quarantine treatments is to reduce the probability of any AR worms being introduced onto the farm. (If any resistant worms do survive the quarantine treatment, then their numbers should be so low that the emergence of AR is greatly delayed.) Quarantine should be applied to sheep purchased from other flocks (including rams), and sheep which have been grazing on other farms (or common grazing) where the resistance status is unknown, and is likely to be different from the home farm. The recommendations also apply to introduced goats as they harbour the same worms as sheep. See Section 6.2 of the text, Sustainable Worm Control in Sheep. The objective of quarantine treatments is to reduce the probability of any AR worms being introduced onto the farm. (If any resistant worms do survive the quarantine treatment, then their numbers should be so low that the emergence of AR is greatly delayed.) Quarantine should be applied to sheep purchased from other flocks (including rams), and sheep which have been grazing on other farms (or common grazing) where the resistance status is unknown, and is likely to be different from the home farm. The recommendations also apply to introduced goats as they harbour the same worms as sheep. See Section 6.2 of the text, Sustainable Worm Control in Sheep.

    38. 2. Use effective quarantine strategies Step 1 Treat all introduced sheep and goats with levamisole plus an ML Do not mix, dose sequentially Give full doses of each drug See Section 6.2 of the text, Sustainable Worm Control in Sheep. See Section 6.2 of the text, Sustainable Worm Control in Sheep.

    39. 2. Use effective quarantine strategies Step 2 After treatment, hold animals off pasture for 24-48 hours, to empty out any worm eggs Supply feed and water during that time Collect faeces passed during that time do not apply to pastures consider incineration, for example See Section 6.2 of the text, Sustainable Worm Control in Sheep. See Section 6.2 of the text, Sustainable Worm Control in Sheep.

    40. 2. Use effective quarantine strategies Step 3 Then place sheep on contaminated pastures to allow dilution of eggs from any surviving worm parasites to encourage rapid re-infection with worms endemic to the farm. See Section 6.2 of the text, Sustainable Worm Control in Sheep. See Section 6.2 of the text, Sustainable Worm Control in Sheep.

    41. 3. Test for AR on your farm Sheep farmers must be strongly encouraged to test for AR A knowledge of each drug’s efficacy is fundamental Without this knowledge adequate worm control may not occur sensible drug rotations cannot be planned See Section 6.3 of the text, Sustainable Worm Control in Sheep. See Section 6.3 of the text, Sustainable Worm Control in Sheep.

    42. 4. Administer anthelmintics effectively Dose for the heaviest in the group Check the gun is working satisfactorily Administer the drug correctly See Section 6.4 of the text, Sustainable Worm Control in Sheep. See Section 6.4 of the text, Sustainable Worm Control in Sheep.

    43. 4. Administer anthelmintics effectively Dose for the heaviest in the group Check the gun is working satisfactorily Administer the drug correctly See Section 6.4 of the text, Sustainable Worm Control in Sheep. See Section 6.4 of the text, Sustainable Worm Control in Sheep.

    44. 4. Administer anthelmintics effectively Dose for the heaviest in the group Check the gun is working satisfactorily Administer the drug correctly See Section 6.4 of the text, Sustainable Worm Control in Sheep. See Section 6.4 of the text, Sustainable Worm Control in Sheep.

    45. 5. Use anthelmintics only when necessary Carefully evaluate the need to dose ewes at tupping See Section 6.5 of the text, Sustainable Worm Control in Sheep. See Section 6.5 of the text, Sustainable Worm Control in Sheep.

    46. 5. Use anthelmintics only when necessary Carefully evaluate the need to dose ewes at tupping If dosing ewes at turn-out use highly efficacious treatments leave some ewes untreated treat well before the end of PPRI See Section 6.5 of the text, Sustainable Worm Control in Sheep. See Section 6.5 of the text, Sustainable Worm Control in Sheep.

    47. 5. Use anthelmintics only when necessary Carefully evaluate the need to dose ewes at tupping If dosing ewes at turn-out use highly efficacious treatments leave some ewes untreated treat well before the end of PPRI Use FEC monitoring to assist decision-making See Section 6.5 of the text, Sustainable Worm Control in Sheep. See Section 6.5 of the text, Sustainable Worm Control in Sheep.

    48. 6. Select the appropriate anthelmintic Use narrow-spectrum drugs when possible eg, closantel for Haemonchus Avoid off-target use particularly in fluke-nematode combinations Rotate anthelmintics when appropriate do not let rotation choice over-rule decisions about quarantine treatment, or narrow-spectrum drugs Consider risks & advantages of persistency of some anthelmintics See Section 6.6 of the text, Sustainable Worm Control in Sheep. See Section 6.6 of the text, Sustainable Worm Control in Sheep.

    49. 7. Preserve susceptible worms on the farm The dose-and-move strategy has been identified as potentially selective for AR part-flock treatment is expected to reduce selection leave 10% untreated (5% to 20%) use highly efficacious treatments (>99% efficacy) delay the ‘move’ after the ‘dose’ See Section 6.7 of the text, Sustainable Worm Control in Sheep. See Section 6.7 of the text, Sustainable Worm Control in Sheep.

    50. 8. Reduce dependence on anthelmintics Use grazing management, rather than anthelmintics, to provide ‘safe’ grazing Cattle can be used in alternate grazing schemes with sheep, but be aware of the risk of calves becoming infected with Nematodirus battus and cattle of all ages becoming infected, and transmitting Haemonchus contortus. Pastures that have not been grazed, such as hay fields, will provide low risk grazing…. or grazing with other species, not including goats. Cattle can be used in alternate grazing schemes with sheep, but be aware of the risk of calves becoming infected with Nematodirus battus and cattle of all ages becoming infected, and transmitting Haemonchus contortus. Pastures that have not been grazed, such as hay fields, will provide low risk grazing…. or grazing with other species, not including goats.

    51. 8. Reduce dependence on anthelmintics Use grazing management, rather than anthelmintics, to provide ‘safe’ grazing Use rams selected for low FEC to breed ewe replacements In flocks that are breeding their own female replacements, the resistance of the flock to worms can be increased by using rams that have been selected for worm resistance. See Sections 8.3, 8.4 and 3.7.5 of the text, Sustainable Worm Control in Sheep. In flocks that are breeding their own female replacements, the resistance of the flock to worms can be increased by using rams that have been selected for worm resistance. See Sections 8.3, 8.4 and 3.7.5 of the text, Sustainable Worm Control in Sheep.

    52. FEC Monitoring Faecal egg counts (FECs) can give a useful guide to the level of parasitism in a flock of sheep But, there are important limitations to their use as a monitoring tool See Section 8.2.1 of the text, Sustainable Worm Control in Sheep. See Section 8.2.1 of the text, Sustainable Worm Control in Sheep.

    53. FEC Monitoring Sample size At least 10 animals should be sampled to estimate a group mean FEC A ‘group’ is a flock of animals of the same sex, age, reproductive status and treatment history, running in the same field The faeces from 10 sheep may be pooled at the laboratory - it should not be mixed before then. See Section 8.2.1 of the text, Sustainable Worm Control in Sheep. See Section 8.2.1 of the text, Sustainable Worm Control in Sheep.

    54. FEC Monitoring What is a suitable group? Animals that are fully-fed and in satisfactory health Results are reported as eggs per gram of faeces If feed intake is impaired, faecal volume is reduced, and results are impossible to interpret See Section 8.2.1 of the text, Sustainable Worm Control in Sheep. See Section 8.2.1 of the text, Sustainable Worm Control in Sheep.

    55. FEC Monitoring Collection of faeces Gather the group, hold quietly in one area, then gather faeces from the pasture See Section 8.2.1 of the text, Sustainable Worm Control in Sheep. See Section 8.2.1 of the text, Sustainable Worm Control in Sheep.

    56. FEC Monitoring Collection of faeces Gather the group, hold quietly in one area, then gather faeces from the pasture Place faeces in airtight container and cool Deliver to laboratory within 48 hours See Section 8.2.1 of the text, Sustainable Worm Control in Sheep. See Section 8.2.1 of the text, Sustainable Worm Control in Sheep.

    57. Collecting faecal samples Gather the group into one place in the field. Remove the dog, and let them stand quietly. For a group of 200 ewes, 3-4 minutes is sufficient. Smaller groups require more time.

    58. Collecting faecal samples Let the sheep move quietly away. Pick up faeces from the pasture and place in a container or small plastic bag. Select only warm, freshly-dropped specimens. Keep each specimen in a separate bag or container.

    59. FEC Monitoring Interpretation of results Interpret with local knowledge Remember: FECs cannot ‘detect’ burdens of immature worms Consider the different relationships between worm numbers and egg numbers in different worm species sheep of different age and reproductive status See Section 8.2.3 of the text, Sustainable Worm Control in Sheep. See Section 8.2.3 of the text, Sustainable Worm Control in Sheep.

    60. FEC Monitoring Price and availability A FEC test is available from a number of laboratories and veterinary practices VLA labs offer a pooled test (10 samples) for Ł15.60 + VAT See Section 8.2.3 of the text, Sustainable Worm Control in Sheep. See Section 8.2.3 of the text, Sustainable Worm Control in Sheep.

    61. Faecal egg count reduction test (FECRT) FECs can be used to detect the presence of AR Simple tests 7 to 14 days post-treatment A quick and easy test for the presence of AR Formal tests Set up with randomised groups, and controls Calculate a percent reduction < 95% reduction implies resistance See Section 8.1.2 of the text, Sustainable Worm Control in Sheep. See Section 8.1.2 of the text, Sustainable Worm Control in Sheep.

    62. The liver fluke - Fasciola hepatica

    63. Liver fluke Liver fluke control is based on a number of drugs (fasciolicides) with different activities Resistance to some fasciolicides has developed in the UK and other countries Control programmes should consider the need to reduce selection pressure for resistance to these drugs Quarantine strategies should aim to reduce the risk of importing resistant fluke. See Section 7 of the text, Sustainable Worm Control in Sheep. See Section 7 of the text, Sustainable Worm Control in Sheep.

    64. From ingestion of the metacercariae from pasture, to an egg-laying adult in the bile ducts takes 10-12 weeks. Different drugs have different efficacies against the immature stages. See Section 7.1 of the text, Sustainable Worm Control in Sheep. From ingestion of the metacercariae from pasture, to an egg-laying adult in the bile ducts takes 10-12 weeks. Different drugs have different efficacies against the immature stages. See Section 7.1 of the text, Sustainable Worm Control in Sheep.

    65. TCB is the most widely used fasciolicide because of its activity against immature fluke. Unfortunately this has led to the development of resistance in several countries and reports of suspected resistance in the UK. Resistance usually manifests first as a failure to kill the youngest immatures, with subsequent re-appearance of fluke eggs in the faeces earlier than would be expected if the drug retained full efficacy. As resistance develops eventually adult fluke are able to survive treatment as well. The possibility of other reasons for fasciolicide failure should always be considered, particularly if animals are in poor condition or may be suffering from liver damage. Where resistance is suspected to a particular product, then an alternative fasciolocide should be considered, taking into account the variations in activity against immature fluke between products. See Section 7.5.1 of the text, Sustainable Worm Control in Sheep. TCB is the most widely used fasciolicide because of its activity against immature fluke. Unfortunately this has led to the development of resistance in several countries and reports of suspected resistance in the UK. Resistance usually manifests first as a failure to kill the youngest immatures, with subsequent re-appearance of fluke eggs in the faeces earlier than would be expected if the drug retained full efficacy. As resistance develops eventually adult fluke are able to survive treatment as well. The possibility of other reasons for fasciolicide failure should always be considered, particularly if animals are in poor condition or may be suffering from liver damage. Where resistance is suspected to a particular product, then an alternative fasciolocide should be considered, taking into account the variations in activity against immature fluke between products. See Section 7.5.1 of the text, Sustainable Worm Control in Sheep.

    66. Preventing the development of resistance to flukicides Rotational use of TCB, closantel or nitroxynil, where appropriate Consider the use of drugs other than TCB when fluke burdens are expected to be entirely or mostly of adult fluke Rotational use of TCB, closantel or nitroxynil should be considered where fasciolicides are used strategically, although additional treatments may be required in years when TCB is not used. Opportunities to avoid the use of TCB should be exploited whenever alternate drugs will give satisfactory levels of control, for example, when used in the spring for treating chronic infections. See Section 7.5.2 of the text, Sustainable Worm Control in Sheep. Rotational use of TCB, closantel or nitroxynil should be considered where fasciolicides are used strategically, although additional treatments may be required in years when TCB is not used. Opportunities to avoid the use of TCB should be exploited whenever alternate drugs will give satisfactory levels of control, for example, when used in the spring for treating chronic infections. See Section 7.5.2 of the text, Sustainable Worm Control in Sheep.

    67. Quarantine treatments for liver fluke Performed for one of three reasons Farm has no snail habitat treat to improve the health of the sheep Farm has snail habitat, but no fluke treat to prevent entry of all fluke Farm has endemic fluke treat to prevent entry of resistant fluke Quarantine treatment strategies for liver fluke in introduced sheep, cattle or goats should be developed for every farm in conjunction with a veterinarian or advisor. The three principal reasons for treatment are : 1.              Sheep may be introduced onto a farm with no known snail habitat and, therefore, no history of fluke infection. The risk of introduced fluke establishing on the farm is very small (or zero, if there is no snail habitat) and treatment in this case is intended to remove any fluke in the sheep for the sake of their health. The consequences of introducing small numbers of fluke, or resistant fluke, are not serious in the long-term. 2.              The farm may have areas considered to be a suitable habitat for snails but no history of fluke infection. The risk of introduced fluke establishing on the farm is considered to be significant so treatment is aimed at removing all fluke, including any resistant fluke. 3.              Liver fluke may be endemic on the farm, so introducing small numbers of fluke will not be serious. However, if the endemic fluke are fully fasciolicide-susceptible, the consequences of introducing resistant fluke are potentially serious. See Section 7.6.1 of the text, Sustainable Worm Control in Sheep. Quarantine treatment strategies for liver fluke in introduced sheep, cattle or goats should be developed for every farm in conjunction with a veterinarian or advisor. The three principal reasons for treatment are : 1.              Sheep may be introduced onto a farm with no known snail habitat and, therefore, no history of fluke infection. The risk of introduced fluke establishing on the farm is very small (or zero, if there is no snail habitat) and treatment in this case is intended to remove any fluke in the sheep for the sake of their health. The consequences of introducing small numbers of fluke, or resistant fluke, are not serious in the long-term. 2.              The farm may have areas considered to be a suitable habitat for snails but no history of fluke infection. The risk of introduced fluke establishing on the farm is considered to be significant so treatment is aimed at removing all fluke, including any resistant fluke. 3.              Liver fluke may be endemic on the farm, so introducing small numbers of fluke will not be serious. However, if the endemic fluke are fully fasciolicide-susceptible, the consequences of introducing resistant fluke are potentially serious. See Section 7.6.1 of the text, Sustainable Worm Control in Sheep.

    68. Quarantine treatments for liver fluke Develop a strategy after considering: Resistance to TCB is still relatively uncommon in the UK Treatment of TCB alone will not remove TCB-resistant fluke Treatment with closantel or nitroxynil is expected to prevent the output of fluke eggs for at least 8 weeks Resistance to closantel and to nitroxynil can occur. Treatment with more than one product will reduce the risk of introducing fluke with resistance to any one product. but the use of two products at the same time may be injurious to health Given the diversity of farm systems, climates and topography, it is not possible to proscribe an appropriate fluke-quarantine strategy for every situation, so we encourage veterinarians to develop a strategy appropriate for each client. After deciding what the aims of quarantine are for each farm (previous slide), these five considerations are provided as reminders of some of the key factors influencing the choice of fascioloicide for quarantine treatment. With regard to point 3 above, treatment with closantel or nitroxynil is expected to prevent the output of fluke eggs for at least 8 weeks and probably more, provided the fluke are susceptible to the drug used. If the introduced sheep are infected with young immature fluke, treatment will have to be repeated after the immatures are old enough to be killed by these products. Also note that: Sheep can pass fluke eggs for up to 3 weeks after adult fluke are killed. It is advised that sheep be kept on quarantine pastures or pastures with no fluke habitat for at least 4 weeks after treatment. FEC monitoring can be used to determine the need for treatments subsequent to the initial one or two. See Section 7.6.2 of the text, Sustainable Worm Control in Sheep. Given the diversity of farm systems, climates and topography, it is not possible to proscribe an appropriate fluke-quarantine strategy for every situation, so we encourage veterinarians to develop a strategy appropriate for each client. After deciding what the aims of quarantine are for each farm (previous slide), these five considerations are provided as reminders of some of the key factors influencing the choice of fascioloicide for quarantine treatment. With regard to point 3 above, treatment with closantel or nitroxynil is expected to prevent the output of fluke eggs for at least 8 weeks and probably more, provided the fluke are susceptible to the drug used. If the introduced sheep are infected with young immature fluke, treatment will have to be repeated after the immatures are old enough to be killed by these products. Also note that: Sheep can pass fluke eggs for up to 3 weeks after adult fluke are killed. It is advised that sheep be kept on quarantine pastures or pastures with no fluke habitat for at least 4 weeks after treatment. FEC monitoring can be used to determine the need for treatments subsequent to the initial one or two. See Section 7.6.2 of the text, Sustainable Worm Control in Sheep.

    69. The end This presentation was brought to you by SCOPS. Sustainable Control of Parasites in Sheep. See also www.nationalsheep.org.uk This powerpoint presentation has been prepared by Lesley Stubbings, LSSC Ltd, and Kym Abbott, Royal Veterinary College, on behalf of SCOPS. We acknowledge the contribution of Professor MA Taylor in preparation of the Technical Manual which has been used as a source document for the information presented here. We also acknowledge the assistance of members of SCOPS, and others, who read drafts of the manual, previewed the presentations, and provided valuable feedback which helped in the preparation of these resources.This powerpoint presentation has been prepared by Lesley Stubbings, LSSC Ltd, and Kym Abbott, Royal Veterinary College, on behalf of SCOPS. We acknowledge the contribution of Professor MA Taylor in preparation of the Technical Manual which has been used as a source document for the information presented here. We also acknowledge the assistance of members of SCOPS, and others, who read drafts of the manual, previewed the presentations, and provided valuable feedback which helped in the preparation of these resources.

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