Abstract
Anthelmintic resistance is a threat to global food security. In order to alleviate the selection pressure for resistance and maintain drug efficacy, management strategies increasingly aim to preserve a proportion of the parasite population in ‘refugia’, unexposed to treatment. While persuasive in its logic, and widely advocated as best practice, evidence for the ability of refugia-based approaches to slow the development of drug resistance in parasitic helminths is currently limited. Moreover, the conditions needed for refugia to work, or how transferable those are between parasite-host systems, are not known. This review, born of an international workshop, seeks to deconstruct the concept of refugia and examine its assumptions and applicability in different situations. We conclude that factors potentially important to refugia, such as the fitness cost of drug resistance, the degree of mixing between parasite sub-populations selected through treatment or not, and the impact of parasite life-history, genetics and environment on the population dynamics of resistance, vary widely between systems. The success of attempts to generate refugia to limit anthelmintic drug resistance are therefore likely to be highly dependent on the system in hand. Additional research is needed on the concept of refugia and the underlying principles for its application across systems, as well as empirical studies within systems that prove and optimise its usefulness.
Highlights
The term ‘refugium’ is classically defined as an area in which a population of organisms can survive through a period of unfavourable conditions
Many of the factors influencing the success of refugia-based approaches in control of GI nematodes were covered in a comprehensive review (Kenyon et al, 2009); we limit our discussion to the impact of the fitness costs of resistance, the influence of parasite life-history traits on the success of refugiabased strategies and the use of modelling approaches
This case illustrates that risk factors for anthelmintic resistance inferred in one system might not hold in others, and that general principles of how refugia impact on the development of drug resistance are elusive in practice
Summary
The term ‘refugium’ is classically defined as an area in which a population of organisms can survive through a period of unfavourable conditions. Refugia-based control for livestock parasites has gained increasing traction in the last 20 years, starting with the ‘call to arms’ by van Wyk (2001), who proposed that refugia should be incorporated more widely into rational anthelmintic use as a means of slowing the spread of resistance. This frequently relies upon treatment of only a proportion of animals, rather than the whole group, leaving some part of the parasite population untreated and free from the selection pressure applied by exposure to drug. This short paper summarises the discussion and presents a critical appraisal of the concept of refugia in principle and practice in three host-parasite systems
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