Anthelmintic resistance: past, present and future

Sangster, Nicholas C.

doi:10.1016/s0020-7519(98)00188-x

Cited by 186 publications

(113 citation statements)

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“…Although many studies have enlightened the molecular basis for resistance to diverse anthelmintic families, reviewed by Sangster [81], few literature data are available concerning the factors responsible for anthelmintic resistance. It is commonly accepted that resistant genes exist as rare alleles in natural populations [55,75,76], and that anthelmintic resistance develops when selection pressure is high.…”

Section: Introductionmentioning

confidence: 99%

Sheep and goat nematode resistance to anthelmintics: pro and cons among breeding management factors

et al. 2002

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-Although the molecular bases of resistance to anthelmintic families have been intensively studied, the contributing factors for the development of anthelmintic resistance are less well known. Clear recommendations must be given to farmers in order to delay the onset of anthelmintic resistance. Until now, the main advice has concerned the reduction of treatment frequency in order to slow down the spread of resistance. Anthelmintic resistance development depends mostly on an efficient selection pressure. This means that a high treatment frequency is neither necessary nor sufficient to select for resistance. The contribution of resistant worms, which have survived an anthelmintic treatment, to the subsequent generation is the key factor that controls resistance spread. This point is illustrated by five surveys conducted on sheep and goat farms from France and Morocco. In the 52 farms studied, less than three anthelmintic treatments were given each year. Three characteristics of breeding management can be identified in the build up of anthelmintic resistance: (1) the introduction of resistant worms through the purchase of sheep/goats or the use of common pastures, grazed by several herds/flocks, (2) under-dosing of hosts and the repeated use of one class of drugs, (3) the size of the population in refugia (infective larvae on pastures) at the time of the treatment. The role played by these breeding management factors in selecting for resistance is discussed. The most efficient way to limit the increase of anthelmintic resistance remains the reduction of the selection pressure by drugs, and optimal timing to maximise their efficacy. Bien que les bases moléculaires de la résistance aux différentes familles d'anthelminthiques aient été très étudiées, les facteurs permettant le développement de la résistance anthelminthique sont moins bien connus. Des recommandations claires sont nécessaires aux éleveurs si l'on souhaite retarder l'apparition de la résistance aux anthelminthiques. La principale recommandation a consisté à réduire la fréquence des traitements de façon à ralentir le développement de la résis-tance. Le développement de la résistance anthelminthique dépend essentiellement d'une pression de sélection efficace. Cela signifie qu'une forte fréquence de traitements n'est ni nécessaire ni suffisante pour sélectionner la résistance. La contribution des vers résistants, qui ont survécu au traitement anthelminthique, à la génération suivante est le facteur clé qui contrôle le développement de la résis-tance. Ce point est illustré par cinq enquêtes réalisées dans des élevages ovins et caprins de France et du Maroc. Dans les 52 élevages étudiés, moins de trois traitements anthelminthiques par an étaient réalisés. Trois conditions d'élevage ont pu être mises en évidence comme étant impliquées dans le dé-veloppement de la résistance anthelminthique :

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Section: Introductionmentioning

confidence: 99%

Sheep and goat nematode resistance to anthelmintics: pro and cons among breeding management factors

et al. 2002

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“…which has resulted in the emergence of anthelmintic-resistant parasites and increased host susceptibility (Sangster, 1999;Jackson and Coop, 2000). The methodology for models belonging to category 3 differs from those of the other categories, as they concentrate less on the dynamic processes during infection of an individual host, but more on the transmission of pathogens and resulting evolutionary processes in the population.…”

Section: Three Categories Of Host-pathogen Interaction Modelsmentioning

confidence: 99%

The role of mathematical models of host–pathogen interactions for livestock health and production – a review

Doeschl‐Wilson

2011

Animal

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Compared with the application of mathematical models to study human diseases, models that describe animal responses to pathogen challenges are relatively rare. The aim of this review is to explain and show the role of mathematical host-pathogen interaction models in providing underpinning knowledge for improving animal health and sustaining livestock production. Existing host-pathogen interaction models can be assigned to one of three categories: (i) models of the infection and immune system dynamics, (ii) models that describe the impact of pathogen challenge on health, survival and production and (iii) models that consider the co-evolution of host and pathogen. State-of-the-art approaches are presented and discussed for models belonging to the first two categories only, as they concentrate on the host-pathogen dynamics within individuals. Models of the third category fall more into the class of epidemiological models, which deserve a review by themselves. An extensive review of published models reveals a rich spectrum of methodologies and approaches adopted in different modelling studies, and a strong discrepancy between models concerning diseases in animals and models aimed at tackling diseases in humans (most of which belong to the first category), with the latter being generally more sophisticated. The importance of accounting for the impact of infection not only on health but also on production poses a considerable challenge to the study of host-pathogen interactions in livestock. This has led to relatively simplistic representations of host-pathogen interaction in existing models for livestock diseases. Although these have proven appropriate for investigating hypotheses concerning the relationships between health and production traits, they do not provide predictions of an animal's response to pathogen challenge of sufficient accuracy that would be required for the design of appropriate disease control strategies. A synthesis between the modelling methodologies adopted in categories 1 and 2 would therefore be desirable. The progress achieved in mathematical modelling to study immunological processes relevant to human diseases, together with the current advances in the generation and analysis of biological data related to animal diseases, offers a great opportunity to develop a new generation of host-pathogen interaction models that take on a fundamental role in the study and control of disease in livestock.

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“…The standard treatment to control the challenge has been the use of anthelminthics [30]. However, as with antibiotics, pathogen resistance to anthelminthics is an increasing problem [25]. Therefore, alternative strategies to control gastrointestinal parasitism are sought.…”

Section: Introductionmentioning

confidence: 99%

Exploring the assumptions underlying genetic variation in host nematode resistance(Open Access publication)

et al. 2008

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-The wide range of genetic parameter estimates for production traits and nematode resistance in sheep obtained from field studies gives rise to much speculation. Using a mathematical model describing host -parasite interactions in a genetically heterogeneous lamb population, we investigated the consequence of: (i) genetic relationships between underlying growth and immunological traits on estimated genetic parameters for performance and nematode resistance, and (ii) alterations in resource allocation on these parameter estimates. Altering genetic correlations between underlying growth and immunological traits had large impacts on estimated genetic parameters for production and resistance traits. Extreme parameter values observed from field studies could only be reproduced by assuming genetic relationships between the underlying input traits. Altering preferences in the resource allocation had less pronounced effects on the genetic parameters for the same traits. Effects were stronger when allocation shifted towards growth, in which case worm burden and faecal egg counts increased and genetic correlations between these resistance traits and body weight became stronger. Our study has implications for the biological interpretation of field data, and for the prediction of selection response from breeding for nematode resistance. It demonstrates the profound impact that moderate levels of pleiotropy and linkage may have on observed genetic parameters, and hence on outcomes of selection for nematode resistance. gastro-intestinal parasites

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Anthelmintic resistance: past, present and future

Cited by 186 publications

References 50 publications

Sheep and goat nematode resistance to anthelmintics: pro and cons among breeding management factors

Sheep and goat nematode resistance to anthelmintics: pro and cons among breeding management factors

The role of mathematical models of host–pathogen interactions for livestock health and production – a review

Exploring the assumptions underlying genetic variation in host nematode resistance(Open Access publication)

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