Research
Research EDITORIAL
Towards cost-effective fluke control in cattle J. van Dijk and P. J. Skuce CATTLE and sheep farmers across the UK are concerned that it is becoming increasingly difficult to control the liver fluke, Fasciola hepatica, in their livestock. There is considerable variability in the incidence of clinical fasciolosis between years but, for the past 15 years, the overall trend has definitely been upwards, while the area where fasciolosis risk is significant has increased (van Dijk and others 2010). At least in part, these trends can be explained by changes in weather patterns, which increase the abundance of infective stages at pasture and/or the mud snail intermediate host (Caminade and others 2015). Meanwhile, in sheep flocks, resistance to triclabendazole, the only flukicide with activity against immature and adult flukes, is limiting treatment options (Fairweather 2011, Daniel and others 2012). Flukicide resistance has, to our knowledge, not yet been diagnosed in cattle. This may be related to the less frequent application of flukicides to cattle herds but, as beef cattle may well ingest resistant worms when co-grazing with sheep, may also reflect the lack of a validated diagnostic test applicable under field conditions. Developing and validating such a test for cattle (based on composite egg count and/or coproantigen ELISA) is one of the objectives
J. van Dijk, DVM, PhD, MRCVS, Institute of Infection and Global Health, Department of Epidemiology and Population Health, University of Liverpool, Leahurst, Cheshire CH64 7TE, UK e-mail: [email protected] P. J. Skuce, BSc, PhD, Moredun Research Institute, Pentlands Science Park, Edinburgh EH26 0PZ, UK
of a new Biotechnology and Biological Sciences Research Council (Dairy and Beef Levy Board) co-funded research project. This initiative is also working on a rapid diagnostic test to distinguish between liver fluke and rumen fluke infections, thereby addressing important diagnostic gaps in beef herds (Charlier and others 2014a). Once parasite presence has been confirmed on a farm, many questions remain about the optimal control strategy for cattle herds. Fencing off of ‘flukey areas’ has long been advocated but, surprisingly, knowledge on the exact location of snails and infectious cysts on pasture is lacking. It is rarely feasible to fence off large areas and, especially with the changing seasonality of metacercarial abundance, the timeframe over which this strategy would need to be deployed is difficult to define. F hepatica will, for the foreseeable future, have to be controlled mainly by anthelmintic drugs. Use of flukicides in cattle has at least two aims: the shorter term objective is to counteract the direct effects of infection on production levels, and the longer term objective is lowering future infective pressure at pasture, for example, by decreasing the number of eggs shed by infected animals. Both of these effects will need to be part of cost-benefit analyses of treatments. At first view, the direct effect on production levels (weight gain and/or litres of milk per time unit) appears to be easily quantifiable (for example, Charlier and others 2007). However, at the farm level, it is entirely dependent on the timing of drug application and is therefore far from clear-cut. If drugs prevent the establishment of parasites, then the effect will be far greater than when drugs are applied to remove established
March 28, 2015 | Veterinary Record | 331
Research Image: Moredun Research Institute
is most cost-effective and adult worms. A study by how is drug activity best Forbes and others (2014), preserved? Farm-based drug summarised on p 333 efficacy studies like the one of this issue of Veterinary by Forbes and others (2014), Record, provides important as well as pasture population insights. Over a period dynamics studies, are much of 112 days, uninfected needed if we are to truly growing young beef cattle quantify the short- and longgained, on average, 20.5 kg term cost-effectiveness of more than those carrying a treatments. patent infection. However, cattle diagnosed as infected at the start of the study, Acknowledgements and then treated with a The authors would like flukicide, gained only 8 to acknowledge financial kg more than infected support of the EU Seventh but untreated animals. In Framework Programme, other words, a ‘preventive’ the GLOWORM project treatment is far more likely (Grant agreement to be cost-effective than a No 288975CP-TPFIG 1: Thickened bile ducts in the liver of a cow chronically infected with ‘curative’ one. As, in more KBBE.2011.1.3-04) and Fasciola hepatica. Fibrosis could shield flukes from contact with anthelmintic chronic infections, flukes the BBSRC Industrial compounds, leading to ‘pseudo-resistance’ will become encapsulated Partnership Award (BBSRCin which animals (for the latest information, in thickened bile ducts (Fig 1), treatment of IPA BB/K015591/1). consult the Veterinary Medicines Directorate such cases will also be less likely to remove References website, www.vmd.defra.gov.uk). the adult worm burden. It is therefore vital Caminade, C., van Dijk, J., Baylis, M. & In the UK, in lactating dairy cattle, to time the application of anthelmintic drugs Williams, D. (2015) Modelling recent and future the choice is limited to albendazole and correctly. climatic suitability for fasciolosis in Europe. Geospatial Health (In press) oxyclozanide (milk withhold 60 hours Periods of infection risk can be detected Charlier, J., Duchateau, L., Claerebout, and 72 hours, respectively) with neither using real-time metacercarial counts but this E., Williams, D. & Vercruysse, J. (2007) drug being claimed to be effective against is technically challenging and very labourAssociations between anti-Fasciola hepatica antibody levels in bulk-tank milk samples and production paramflukes in animals below seven to 10 weeks intensive. The recently completed EU-funded eters in dairy herds. Preventative Veterinary Medicine 78, of age. Triclabendazole can be applied to GLOWORM project has developed 57-66 cattle at dry-off (milk withhold 50 days). mathematical models which, for the first Charlier, J., Vercruysse, J., Morgan, E., This may improve yield but, in year-round time, appear to accurately predict the timing van Dijk, J. & Williams, D. J. (2014a) Recent advances in the diagnosis, impact on production and calving herds, the longer term effects of of increased metacercarial abundance from prediction of Fasciola hepatica in cattle. Parasitology 141, such small-group treatments on fluke climatic variables. If brought to the field, 326-335 population dynamics is entirely unclear. In these models will guide the timing of drug Charlier, J., Morgan, E. R., Rinaldi, L., van Dijk, J., Demeler, J., Höglund, J., beef cattle, the full spectrum of flukicides is application, thereby increasing its efficacy. Hertzberg, H. & OTHERS (2014b) Practices to available and the advice has normally been Such models also provide the only way to optimise gastrointestinal nematode control on sheep, to dose with triclabendazole in autumn/ quantify the second, longer term, effect of goat and cattle farms in Europe using targeted (selecat housing (for example, with a view to tive) treatments. Veterinary Record doi:10.1136/vr.102512 drug applications on parasite population Daniel, R., van Dijk, J., Jenkins, T., Akca, A., removing the youngest flukes as well as dynamics. For example, although validation Mearns, R. & Williams, D. J. (2012) Composite adults) or to repeat the dose, removing older efforts are ongoing, initial modelling output faecal egg count reduction test to detect resistance to flukes only at a specified interval (to remove seems to clearly suggest that treatments of triclabendazole in Fasciola hepatica. Veterinary Record doi:10.1136/vr.100588 adults which have matured since the first cattle in late spring (May or June) appears Fairweather, I. (2011) Raising the bar on reportapplication). Forbes and others (2014) show to be more effective in terms of lowering ing ‘triclabendazole resistance’. Veterinary Record 168, that the amount of weight gain seen in cattle metacercarial load during the period of 514-515 Forbes, A. B., Reddick, D. & Stear, M. J. (2014) drenched at housing was not significantly highest risk (autumn) in the same year, than Efficacy of treatment of cattle for liver fluke at housinfluenced by the compound used, treatments applied in other months. It is ing: influence of differences in flukicidal activity against thereby casting doubt over the direct costquite likely that the timing of treatments juvenile Fasciola hepatica. Veterinary Record doi:10.1136/ effectiveness of a second treatment in housed will have to be adjusted in future and the vr.102720 van Dijk, J., Sargison, N. D., Kenyon, F. & cattle. Last but not least, it is not known optimal timing may not be predictable using Skuce, P. J. (2010) Climate change and infectious dishow available drugs should best be rotated ‘common sense’ only. On the other hand, ease: helminthological challenges to farmed ruminants to prevent the development of anthelmintic model predictions should only provide in temperate regions. Animal 4, 377-392 resistance. Targeted selective treatment guidance, which will have to be validated in doi: 10.1136/vr.h1509 approaches, which have been successfully field studies. Unfortunately, such studies are applied to preserve refugia in roundworms scarce. For example, Forbes and others (2014) (Charlier and others 2014b), have thus far report that there have only been two field not been used in Fasciola control. studies examining the seasonal population In conclusion, as important gaps in our structure of flukes in cattle. knowledge of the population dynamics of Apart from uncertainty about the best F hepatica are starting to be addressed, and timing for drug applications, it is also unclear much-needed diagnostic tests are developed, which anthelmintic compounds should be now is a good time to address essential yet used at each application. Due to concerns unclear factors for fluke control: which about chemical residues in meat and milk, anthelmintic compounds should be used and there have been significant recent changes at which time of the year, which treatment with regards to which flukicides can be used 332 | Veterinary Record | March 28, 2015
Copyright of Veterinary Record: Journal of the British Veterinary Association is the property of BMJ Publishing Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
Research EDITORIAL
Towards cost-effective fluke control in cattle J. van Dijk and P. J. Skuce CATTLE and sheep farmers across the UK are concerned that it is becoming increasingly difficult to control the liver fluke, Fasciola hepatica, in their livestock. There is considerable variability in the incidence of clinical fasciolosis between years but, for the past 15 years, the overall trend has definitely been upwards, while the area where fasciolosis risk is significant has increased (van Dijk and others 2010). At least in part, these trends can be explained by changes in weather patterns, which increase the abundance of infective stages at pasture and/or the mud snail intermediate host (Caminade and others 2015). Meanwhile, in sheep flocks, resistance to triclabendazole, the only flukicide with activity against immature and adult flukes, is limiting treatment options (Fairweather 2011, Daniel and others 2012). Flukicide resistance has, to our knowledge, not yet been diagnosed in cattle. This may be related to the less frequent application of flukicides to cattle herds but, as beef cattle may well ingest resistant worms when co-grazing with sheep, may also reflect the lack of a validated diagnostic test applicable under field conditions. Developing and validating such a test for cattle (based on composite egg count and/or coproantigen ELISA) is one of the objectives
J. van Dijk, DVM, PhD, MRCVS, Institute of Infection and Global Health, Department of Epidemiology and Population Health, University of Liverpool, Leahurst, Cheshire CH64 7TE, UK e-mail: [email protected] P. J. Skuce, BSc, PhD, Moredun Research Institute, Pentlands Science Park, Edinburgh EH26 0PZ, UK
of a new Biotechnology and Biological Sciences Research Council (Dairy and Beef Levy Board) co-funded research project. This initiative is also working on a rapid diagnostic test to distinguish between liver fluke and rumen fluke infections, thereby addressing important diagnostic gaps in beef herds (Charlier and others 2014a). Once parasite presence has been confirmed on a farm, many questions remain about the optimal control strategy for cattle herds. Fencing off of ‘flukey areas’ has long been advocated but, surprisingly, knowledge on the exact location of snails and infectious cysts on pasture is lacking. It is rarely feasible to fence off large areas and, especially with the changing seasonality of metacercarial abundance, the timeframe over which this strategy would need to be deployed is difficult to define. F hepatica will, for the foreseeable future, have to be controlled mainly by anthelmintic drugs. Use of flukicides in cattle has at least two aims: the shorter term objective is to counteract the direct effects of infection on production levels, and the longer term objective is lowering future infective pressure at pasture, for example, by decreasing the number of eggs shed by infected animals. Both of these effects will need to be part of cost-benefit analyses of treatments. At first view, the direct effect on production levels (weight gain and/or litres of milk per time unit) appears to be easily quantifiable (for example, Charlier and others 2007). However, at the farm level, it is entirely dependent on the timing of drug application and is therefore far from clear-cut. If drugs prevent the establishment of parasites, then the effect will be far greater than when drugs are applied to remove established
March 28, 2015 | Veterinary Record | 331
Research Image: Moredun Research Institute
is most cost-effective and adult worms. A study by how is drug activity best Forbes and others (2014), preserved? Farm-based drug summarised on p 333 efficacy studies like the one of this issue of Veterinary by Forbes and others (2014), Record, provides important as well as pasture population insights. Over a period dynamics studies, are much of 112 days, uninfected needed if we are to truly growing young beef cattle quantify the short- and longgained, on average, 20.5 kg term cost-effectiveness of more than those carrying a treatments. patent infection. However, cattle diagnosed as infected at the start of the study, Acknowledgements and then treated with a The authors would like flukicide, gained only 8 to acknowledge financial kg more than infected support of the EU Seventh but untreated animals. In Framework Programme, other words, a ‘preventive’ the GLOWORM project treatment is far more likely (Grant agreement to be cost-effective than a No 288975CP-TPFIG 1: Thickened bile ducts in the liver of a cow chronically infected with ‘curative’ one. As, in more KBBE.2011.1.3-04) and Fasciola hepatica. Fibrosis could shield flukes from contact with anthelmintic chronic infections, flukes the BBSRC Industrial compounds, leading to ‘pseudo-resistance’ will become encapsulated Partnership Award (BBSRCin which animals (for the latest information, in thickened bile ducts (Fig 1), treatment of IPA BB/K015591/1). consult the Veterinary Medicines Directorate such cases will also be less likely to remove References website, www.vmd.defra.gov.uk). the adult worm burden. It is therefore vital Caminade, C., van Dijk, J., Baylis, M. & In the UK, in lactating dairy cattle, to time the application of anthelmintic drugs Williams, D. (2015) Modelling recent and future the choice is limited to albendazole and correctly. climatic suitability for fasciolosis in Europe. Geospatial Health (In press) oxyclozanide (milk withhold 60 hours Periods of infection risk can be detected Charlier, J., Duchateau, L., Claerebout, and 72 hours, respectively) with neither using real-time metacercarial counts but this E., Williams, D. & Vercruysse, J. (2007) drug being claimed to be effective against is technically challenging and very labourAssociations between anti-Fasciola hepatica antibody levels in bulk-tank milk samples and production paramflukes in animals below seven to 10 weeks intensive. The recently completed EU-funded eters in dairy herds. Preventative Veterinary Medicine 78, of age. Triclabendazole can be applied to GLOWORM project has developed 57-66 cattle at dry-off (milk withhold 50 days). mathematical models which, for the first Charlier, J., Vercruysse, J., Morgan, E., This may improve yield but, in year-round time, appear to accurately predict the timing van Dijk, J. & Williams, D. J. (2014a) Recent advances in the diagnosis, impact on production and calving herds, the longer term effects of of increased metacercarial abundance from prediction of Fasciola hepatica in cattle. Parasitology 141, such small-group treatments on fluke climatic variables. If brought to the field, 326-335 population dynamics is entirely unclear. In these models will guide the timing of drug Charlier, J., Morgan, E. R., Rinaldi, L., van Dijk, J., Demeler, J., Höglund, J., beef cattle, the full spectrum of flukicides is application, thereby increasing its efficacy. Hertzberg, H. & OTHERS (2014b) Practices to available and the advice has normally been Such models also provide the only way to optimise gastrointestinal nematode control on sheep, to dose with triclabendazole in autumn/ quantify the second, longer term, effect of goat and cattle farms in Europe using targeted (selecat housing (for example, with a view to tive) treatments. Veterinary Record doi:10.1136/vr.102512 drug applications on parasite population Daniel, R., van Dijk, J., Jenkins, T., Akca, A., removing the youngest flukes as well as dynamics. For example, although validation Mearns, R. & Williams, D. J. (2012) Composite adults) or to repeat the dose, removing older efforts are ongoing, initial modelling output faecal egg count reduction test to detect resistance to flukes only at a specified interval (to remove seems to clearly suggest that treatments of triclabendazole in Fasciola hepatica. Veterinary Record doi:10.1136/vr.100588 adults which have matured since the first cattle in late spring (May or June) appears Fairweather, I. (2011) Raising the bar on reportapplication). Forbes and others (2014) show to be more effective in terms of lowering ing ‘triclabendazole resistance’. Veterinary Record 168, that the amount of weight gain seen in cattle metacercarial load during the period of 514-515 Forbes, A. B., Reddick, D. & Stear, M. J. (2014) drenched at housing was not significantly highest risk (autumn) in the same year, than Efficacy of treatment of cattle for liver fluke at housinfluenced by the compound used, treatments applied in other months. It is ing: influence of differences in flukicidal activity against thereby casting doubt over the direct costquite likely that the timing of treatments juvenile Fasciola hepatica. Veterinary Record doi:10.1136/ effectiveness of a second treatment in housed will have to be adjusted in future and the vr.102720 van Dijk, J., Sargison, N. D., Kenyon, F. & cattle. Last but not least, it is not known optimal timing may not be predictable using Skuce, P. J. (2010) Climate change and infectious dishow available drugs should best be rotated ‘common sense’ only. On the other hand, ease: helminthological challenges to farmed ruminants to prevent the development of anthelmintic model predictions should only provide in temperate regions. Animal 4, 377-392 resistance. Targeted selective treatment guidance, which will have to be validated in doi: 10.1136/vr.h1509 approaches, which have been successfully field studies. Unfortunately, such studies are applied to preserve refugia in roundworms scarce. For example, Forbes and others (2014) (Charlier and others 2014b), have thus far report that there have only been two field not been used in Fasciola control. studies examining the seasonal population In conclusion, as important gaps in our structure of flukes in cattle. knowledge of the population dynamics of Apart from uncertainty about the best F hepatica are starting to be addressed, and timing for drug applications, it is also unclear much-needed diagnostic tests are developed, which anthelmintic compounds should be now is a good time to address essential yet used at each application. Due to concerns unclear factors for fluke control: which about chemical residues in meat and milk, anthelmintic compounds should be used and there have been significant recent changes at which time of the year, which treatment with regards to which flukicides can be used 332 | Veterinary Record | March 28, 2015
Copyright of Veterinary Record: Journal of the British Veterinary Association is the property of BMJ Publishing Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
