Changes in anthelmintic resistance status of Haemonchus contortus and Trichostrongylus colubriformis exposed to different anthelmintic selection pressures in grazing sheep

Waller, P.J.; Donald, A.D.; Dobson, R.J.; Lacey, Ernest; Hennessy, D.R.; Allerton, G.R.; Prichard, Roger K.

doi:10.1016/0020-7519(89)90027-1

Cited by 47 publications

(20 citation statements)

References 11 publications

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“…Over a 5-year period, the use of thiabendazole was found to select against levamisole resistance in T. colubriformis, to a greater extent than natural reversion that occurred in the absence of anthelmintic treatments; however, the level of reversion in both cases was small and in neither case did full susceptibility return (Waller et al 1989). Ivermectin resistance in O. circumcincta rapidly re-emerged in goats after a 5-year period during which macrocyclic-lactone anthelmintics were not used (Pomroy et al 1998).…”

Section: Reversion Toward Susceptibilitymentioning

confidence: 80%

“…However, as these studies also usually include the use of more than one anthelmintic, they cannot exclude the possibility of counterselection. Regular use of levamisole to control benzimidazoleresistant trichostrongylids led to a reduction in the level of benzimidazole resistance in O. circumcincta after 4 years (Martin 1987;Waller et al 1988) and in T. colubriformis after 8 years (Waller et al 1989). However, reversion was not to full susceptibility and re-introduction of benzimidazoles led to the rapid re-emergence of benzimidazole resistance to former levels in all cases.…”

Section: Reversion Toward Susceptibilitymentioning

confidence: 95%

“…In another study, the use of levamisole for a 15-year period did not affect the level of benzimidazole resistance in O. circumcincta (Jackson and Coop 2000). No variation was found in the level of benzimidazole resistance in H. contortus after using levamisole for 6 years (Borgesteede and Duyn 1989) or 8 years (Waller et al 1989). Others have studied the possibility that fitness of resistant genotypes increases with the level of resistance, thus influencing the potential for reversion.…”

Section: Reversion Toward Susceptibilitymentioning

confidence: 96%

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Anthelmintic resistance in New Zealand

Leathwick¹,

Pomroy

Heath

2001

New Zealand Veterinary Journal

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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.

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Section: Reversion Toward Susceptibilitymentioning

confidence: 80%

Section: Reversion Toward Susceptibilitymentioning

confidence: 95%

Section: Reversion Toward Susceptibilitymentioning

confidence: 96%

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Anthelmintic resistance in New Zealand

Leathwick¹,

Pomroy

Heath

2001

New Zealand Veterinary Journal

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“…This solution is not sustainable from the residues, environment and efficacy point of views. An alternation of BZ and another drug has been proposed ( [Waller et al, 1989], [McKenna, 1990] and [Grimshaw et al, 1996]). Some studies had tested the anthelmintic alternation in experimental conditions, at a time where the genetic main mechanisms of resistance to BZ was not known.…”

Section: Introductionmentioning

confidence: 99%

“…BZ-resistant nematodes are efficiently controlled by imidazothiazoles or macrocyclic lactones ( [Overend et al, 1994] and [Waruiru et al, 1996]). To maintain the BZ drug efficacy and to control the evolution of resistance, the alternation of drugs or a simultaneous use of minimum two molecules had been proposed ([Donald et al, 1980], [Prichard et al, 1980], [Dobson et al, 1987], [Waller et al, 1989], [Uhlinger and Kristula, 1992], [Coles, 1994], [McKenna et al, 1996] and [Andrews, 2000]). Formulations permitting the simultaneous use of two or three molecules from the existing three main groups of anthelmintics are available in countries such as Australia (Q-drench ® , Triton ® , etc.…”

Section: Introductionmentioning

confidence: 99%

Alternation of anthelmintic treatments: A molecular evaluation for benzimidazole resistance in nematodes

Leignel

Silvestre

Humbert

et al. 2010

Veterinary Parasitology

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The evolution of benzimidazoles (BZ) resistance in Teladorsagia circumcincta was investigated in a controlled trial with lambs, submitted to different treatment regimens. Four paddocks were seeded with a T. circumcincta strain constituted by 25% of BZ-resistant nematodes. Ten permanent lambs were allocated to each paddock, from April to November in order to renew the contamination of pasture. Monthly, three tracer lambs were allocated in each paddock. BZresistant nematode frequency was determined (PCR diagnosis). The faecal egg count reduction test (permanent lambs) and the number of nematodes in lambs were also determined (permanent and tracer lambs). Four different regimens of treatments were performed: control, levamisole (a non-BZ drug), fenbendazole (a BZ drug), and an alternation of levamisole and fenbendazole every second treatment. The same protocol was repeated on two consecutive grazing seasons, increasing the number of treatments (3 in first year and 5 in second year). The proportions of BZ-resistant nematodes did not change during all the study in both the control and the levamisole paddocks, supporting an equal global fitness of BZ-resistant and susceptible nematodes. Thus, no reversion of BZ resistance is to be expected. In the alternated drug group and in the BZ treated group, BZ-resistant nematodes increased from 25% to 47% and to 78%, respectively. BZ resistance increased proportionally to the selective pressure (number of BZ treatments). The drug alternation is not a good solution to delay importantly the evolution of resistance when more than 25% of nematodes are BZ-resistant. This study is the first evaluation of BZ-resistance evolution (using individual genotyping) in controlled conditions. It showed that when a monogenic anthelmintic resistance is established at 25% in a sexually reproducing nematode population, it seems to be impossible to prevent its increase even when using limited number of BZ treatments.

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Drug Resistance in Nematodes

Prichard¹

2017

Antimicrobial Drug Resistance

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Changes in anthelmintic resistance status of Haemonchus contortus and Trichostrongylus colubriformis exposed to different anthelmintic selection pressures in grazing sheep

Cited by 47 publications

References 11 publications

Anthelmintic resistance in New Zealand

Anthelmintic resistance in New Zealand

Alternation of anthelmintic treatments: A molecular evaluation for benzimidazole resistance in nematodes

Drug Resistance in Nematodes

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