Exploration of the epidemiological consequences of resistance to gastro-intestinal parasitism and grazing management of sheep through a mathematical model

Laurenson, Yan C.S.M.; Kyriazakis, Ι.; Forbes, Andrew Benjamin; Bishop, Stephen

doi:10.1016/j.vetpar.2012.05.005

Cited by 14 publications

(23 citation statements)

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“…As such, this encompasses the timing of any targeted treatment (TT) strategy. Importantly, all scenarios were modelled such that each treatment group grazed independently on separate pastures and thereby incorporated the epidemiological benefit of anthelmintic treatment strategies (Laurenson et al, 2012a).…”

Section: Simulation Procedures and In Silico Experimental Designmentioning

confidence: 99%

“…Anthelmintic treatment is known to select for resistance in proportion to the nematode population in refugia (Martin et al, 1981;Michel, 1985), and consequently practices such as administering anthelmintics prior to a move to a low worm-risk pasture should be carefully managed (Martin et al, 1985;Waghorn et al, 2009). Whilst grazing management (Waller, 2006b) and the host immune response (Laurenson et al, 2012a) affect nematode epidemiology, environmental conditions experienced by the supra-population are the predominant factor impacting upon the nematode population in refugia (Stromberg, 1997;O'Connor et al, 2006;van Dijk et al, 2010;Morgan and van Dijk, 2012;Rose et al, 2015). Consequent fluctuations in the level of pasture contamination have led to the proposal of targeting whole flock treatments (TT, targeted treatment) at times when the supra-population provides a large refugia pool (Kenyon et al, 2009;Kenyon and Jackson, 2012), coinciding with periods in which the hosts will be exposed to a high level of infective larval challenge.…”

Section: Introductionmentioning

confidence: 99%

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Which is the best phenotypic trait for use in a targeted selective treatment strategy for growing lambs in temperate climates?

Laurenson

Kahn

Bishop

et al. 2016

Veterinary Parasitology

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Section: Simulation Procedures and In Silico Experimental Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Which is the best phenotypic trait for use in a targeted selective treatment strategy for growing lambs in temperate climates?

Laurenson

Kahn

Bishop

et al. 2016

Veterinary Parasitology

Self Cite

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“…Several modeling studies have shown that whilst the direct impacts of selection for reduced FEC on performance traits depend on the genetic correlations between traits (e.g., Vagenas et al, 2007; Doeschl-Wilson et al, 2008), the reductions in pasture contamination (from reduced FEC) potentially lead to substantially increased performance (Bishop and Stear, 1997, 1999; Laurenson et al, 2012). Various experimental studies now support these theoretical predictions of epidemiological benefits arising from populations of animals excreting fewer eggs (Gruner et al, 2002; Leathwick et al, 2002; Williams et al, 2010).…”

Section: Application To Nematode Infectionsmentioning

confidence: 99%

A consideration of resistance and tolerance for ruminant nematode infections

Bishop¹

2012

Front. Gene.

104

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Debates on the relative merits of resistance (the ability of the host to control the parasite lifecycle) and tolerance (the net impact of infection on host performance) are often lively and unhindered by data or evidence. Resistance generally shows continuous, heritable variation but data are sparser for tolerance, the utility of which will depend upon the disease prevalence. Prevalence is a function of group mean resistance and infection pressure, which itself is influenced by mean resistance. Tolerance will have most value for endemic diseases with a high prevalence but will be of little value for low prevalence diseases. The conditionality of tolerance on infection status, and hence resistance, makes it difficult to estimate independently of resistance. Tolerance is potentially tractable for nematode infections, as the prevalence of infection is ca. 100% in animals grazing infected pasture, and infection level can be quantified by faecal egg count (FEC). Whilst individual animal phenotypes for tolerance are difficult to estimate, breeding values are estimable if related animals graze pastures of different contamination levels. Selection for resistance, i.e., FEC, provides both direct and indirect benefits from ever decreased pasture contamination and hence decreased infectious challenge. Modeling and experimental studies have shown that such reductions in pasture contamination may lead to substantially increased performance. It is proposed that selection goals addressing nematode infections should include both resistance and performance under challenging conditions. However, there may be benefits from exploiting large datasets in which sires are used across cohorts differing in infection level, to further explore tolerance. This may help to customise breeding objectives, with tolerance given greater weight in heavily parasitized environments.

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“…Indeed, the in silico approach allows for multiple scenarios to be considered without having to resort to experimentation once the model was validated [13–15]. These mechanistic models rely on the input of specific parameters, such as life history traits of the parasitic phase.…”

Section: Introductionmentioning

confidence: 99%

Meta-analysis of the parasitic phase traits of Haemonchus contortus infection in sheep

et al. 2017

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BackgroundThe parasitic nematode Haemonchus contortus shows highly variable life history traits. This highlights the need to have an average estimate and a quantification of the variation around it to calibrate epidemiological models.MethodsThis paper aimed to quantify the main life history traits of H. contortus and to identify explanatory factors affecting these traits using a powerful method based on a systematic review and meta-analysis of current literature. The life history traits considered are: (i) the establishment rate of ingested larvae; (ii) the adult mortality rate; (iii) the fertility (i.e. the number of eggs laid/female/day); and (iv) fecundity of female worms (i.e. the number of eggs per gram of faeces).ResultsA total of 37 papers that report single experimental infection with H. contortus in sheep and published from 1960 to 2015, were reviewed and collated in this meta-analysis. This encompassed 115 experiments on 982 animals. Each trait was analysed using a linear model weighted by its inverse variance. The average (± SE) larval establishment rate was 0.24 ± 0.02, which decreased as a function of the infection dose and host age. An average adult mortality rate of 0.021 ± 0.002) was estimated from the literature. This trait varied as a function of animal age, breed and protective response due to prior exposure to the parasite. Average female fertility was 1295.9 ± 280.4 eggs/female/day and decreased in resistant breeds and previously infected hosts. Average faecal egg count at necropsy was 908.5 ± 487.1 eggs per gram of faeces and varied as a function of infection duration and host resistance. The average sex ratio of H. contortus was 0.51 ± 0.006.ConclusionThis work is the first systematic review to summarise the available information on the parasitic phase of H. contortus in sheep. The results of the meta-analysis provide robust estimates of life history traits for parametrization of epidemiological models, their expected variation according to experimental factors, and provides correlations between these.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-017-2131-7) contains supplementary material, which is available to authorized users.

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Exploration of the epidemiological consequences of resistance to gastro-intestinal parasitism and grazing management of sheep through a mathematical model

Cited by 14 publications

References 47 publications

Which is the best phenotypic trait for use in a targeted selective treatment strategy for growing lambs in temperate climates?

Which is the best phenotypic trait for use in a targeted selective treatment strategy for growing lambs in temperate climates?

A consideration of resistance and tolerance for ruminant nematode infections

Meta-analysis of the parasitic phase traits of Haemonchus contortus infection in sheep

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