Brave or gullible: Testing the concept that leaving susceptible parasites in refugia will slow the development of anthelmintic resistance

Waghorn, T.S.; Leathwick, Dave M.; Miller, C.M.; Atkinson, D. S.

doi:10.1080/00480169.2008.36828

Cited by 60 publications

(32 citation statements)

References 16 publications

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“…Support for the results outlined above has since been provided by another study in New Zealand, that identifi ed a signifi cant association between treatment of ewes pre-lambing with long-acting ML products and the presence of ML resistance (Lawrence et al 2006). However, a second similar, though smaller-scale, study failed to detect such an association (Hughes et al 2007).…”

Section: High-risk Drenching and Stock-management Practicesmentioning

confidence: 77%

Managing anthelmintic resistance: Is it feasible in New Zealand to delay the emergence of resistance to a new anthelmintic class?

Leathwick

Hosking

Bisset

et al. 2009

New Zealand Veterinary Journal

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The recent registration in New Zealand of the first new class of broad-spectrum anthelmintic, for use against nematode parasites of ruminants, in nearly three decades has raised the possibility that parasite management practices could be improved to minimise the emergence of resistance to the new drug. A review of knowledge pertaining to the selection of anthelmintic resistance in nematode parasites of sheep highlights a number of management practices which could be altered to achieve this. A number of previously common practices such as whole-flock treatment of adult ewes around lambing, and treatment of lambs as they are moved onto pastures with low parasite contamination have been clearly identified as high risk for selecting resistant parasites. Once high-risk practices have been identified steps can be taken to either eliminate their use or mitigate the associated risk. Much of the focus on the management of resistance around the world is on the retention of susceptible genotypes in refugia. While approaches to retaining unselected parasites are likely to vary around the world, empirical studies indicate that the practice is likely to be effective at slowing the development of resistance. The challenge for farmers and advisors will be to strike a balance between retaining sufficient susceptible parasites to usefully delay the development of resistance while not unduly compromising animal performance and farm profitability. The merits of combining different classes of anthelmintic in order to slow the development of resistance remains somewhat contentious in some countries. However, the attributes of oral anthelmintics are such that they seem likely to meet most, if not all, of the criteria for combinations to be highly effective at slowing the build-up of resistance in nematode parasites. It is evident that considerable progress has been made in understanding the factors involved in selecting anthelmintic-resistant nematodes since the last broad-spectrum anthelmintic class was released in the early 1980s. Therefore, it should be possible to manage a new class of anthelmintic in such a way as to significantly extend its effective life. The challenge is likely to be in convincing farmers of the merits of adopting such pro-active strategies.

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Section: High-risk Drenching and Stock-management Practicesmentioning

confidence: 77%

Managing anthelmintic resistance: Is it feasible in New Zealand to delay the emergence of resistance to a new anthelmintic class?

Leathwick

Hosking

Bisset

et al. 2009

New Zealand Veterinary Journal

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“…Early recommendations for sustainable parasite control were either based on evidence regarding key molecular processes involved in selection for resistance (Dobson et al, 2001), or simulation models (Leathwick et al, 1995). In recent years, several observational studies (Suter et al, 2004;Lawrence et al, 2006;Hughes et al, 2007;Calvete et al, 2012) and clinical trials Leathwick et al, 2008;Waghorn et al, 2008Waghorn et al, , 2009 have been performed to investigate the association between putative risk factors and AHR. While all these studies may provide valuable information in isolation, they sometimes describe conflicting results.…”

Section: Introductionmentioning

confidence: 99%

A systematic review and meta-analysis of factors associated with anthelmintic resistance in sheep

Falzon

O’Neill

Menzies

et al. 2014

Preventive Veterinary Medicine

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“…intractable resistance to each drug, would be reached more or less simultaneously whether two drugs are rotated or used in series. Their model also indicated that non-treatment of a few animals in order to preserve susceptible worms would delay selection for resistance, as has subsequently been supported by various field studies Leathwick et al, 2006a;2006b;Greer et al, 2009;Waghorn et al, 2008;. Learmount et al (2006) developed a computer model for the United Kingdom to simulate expected egg counts (and therefore predict the timing of expected peaks in faecal egg counts) for a variety of inputs including regional weather data, stocking density, initial pasture contamination levels, parasite species proportions, as well as lambing dates, the timing of flock movements and removal of lambs.…”

mentioning

confidence: 80%

A stochastic model accommodating the FAMACHA© system for estimating worm burdens and associated risk factors in sheep naturally infected with Haemonchus contortus

Reynecke

Wyk

Gummow

et al. 2011

Veterinary Parasitology

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A previously developed multiple regression algorithm was used as the basis of a stochastic model to simulate worm burdens in sheep naturally infected with Haemonchus contortus over five consecutive Haemonchus seasons (November to January/February) on a farm in the summer rainfall region in South Africa, although only one season is discussed. The algorithm associates haemoglobin levels with worm counts in individual animals. Variables were represented by distributions based on FAMACHA © scores and body weights of sheep, and Monte Carlo sampling was used to simulate worm burdens.Under conditions of high disease risk, defined as the sampling event during the worm season with the lowest relative mean haemoglobin level for a class of sheep, the model provided a distribution function for mean class H. contortus burdens and the probability of these occurring.A mean H. contortus burden for ewes (n=130 per sample) of approximately 1 000(range 51 to 28 768) and 2 933 (range 78 to 44 175) for rams (n = 120 per sample) was predicted under these conditions. At the beginning of the worm season when the risk of disease was lowest (i.e. when both classes had their highest estimated mean haemoglobin levels), a mean worm burden of 525 (range 39 to 4910) for ewes and 651 (range 37 to 17260) for rams was predicted. Model indications were that despite being selectively drenched according to FAMACHA © evaluation, 72% of the ewes would maintain their mean worm burden below an arbitrarily selected threshold of 1 000 even when risk of disease was at its highest. In contrast, far fewer rams (27%) remained below this threshold, especially towards the end of the worm season.The model was most sensitive to changes in haemoglobin value, and thus by extrapolation, the haematocrit, which is used as the gold standard for validating the FAMACHA © system. The mean class haemoglobin level at which there was a 50% probability of worm burdens being ≤1000 worms was 7.05 g/dl in ewes and 7.92 g/dl in rams.

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Brave or gullible: Testing the concept that leaving susceptible parasites in refugia will slow the development of anthelmintic resistance

Cited by 60 publications

References 16 publications

Managing anthelmintic resistance: Is it feasible in New Zealand to delay the emergence of resistance to a new anthelmintic class?

Managing anthelmintic resistance: Is it feasible in New Zealand to delay the emergence of resistance to a new anthelmintic class?

A systematic review and meta-analysis of factors associated with anthelmintic resistance in sheep

A stochastic model accommodating the FAMACHA© system for estimating worm burdens and associated risk factors in sheep naturally infected with Haemonchus contortus

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