The parasitic phase of Ostertagia ostertagi: quantification of the main life history traits through systematic review and meta-analysis

Verschave, Sien; Vercruysse, Jozef; Claerebout, Edwin; Rose, Hannah; Morgan, Eric R.; Charlier, Johannes

doi:10.1016/j.ijpara.2014.08.006

Cited by 25 publications

(30 citation statements)

References 84 publications

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“…A trigger of 200 eggs/g has been used previously, however this was defined for mixed infections (O'Shaughnessy et al., 2014a). Although seasonal variation in egg ratios is observed in temperate regions (Dorny et al., 1988, Vercruysse et al., 1988, Verschave et al., 2014), for simplicity it was assumed that an average proportion of 0.4 was O. ostertagi eggs (Dorny et al., 1988, Vercruysse et al., 1988, Hilderson et al., 1990, Ploeger and Kloosterman, 1993, Almería et al., 1996, Areskog et al., 2013, Verschave et al., 2015). The threshold for pepsinogen levels was assumed to be 2 IUT/l and therefore the final group involved treating calves when both FECs greater than 80 eggs/g and pepsinogen levels greater than 2 IUT/l were attained by an individual.…”

Section: Methodsmentioning

confidence: 99%

Modelling the consequences of targeted selective treatment strategies on performance and emergence of anthelmintic resistance amongst grazing calves

Berk

Laurenson

Forbes

et al. 2016

International Journal for Parasitology: Drugs and Drug Resistan

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The development of anthelmintic resistance by helminths can be slowed by maintaining refugia on pasture or in untreated hosts. Targeted selective treatments (TST) may achieve this through the treatment only of individuals that would benefit most from anthelmintic, according to certain criteria. However TST consequences on cattle are uncertain, mainly due to difficulties of comparison between alternative strategies. We developed a mathematical model to compare: 1) the most ‘beneficial’ indicator for treatment selection and 2) the method of selection of calves exposed to Ostertagia ostertagi, i.e. treating a fixed percentage of the population with the lowest (or highest) indicator values versus treating individuals who exceed (or are below) a given indicator threshold. The indicators evaluated were average daily gain (ADG), faecal egg counts (FEC), plasma pepsinogen, combined FEC and plasma pepsinogen, versus random selection of individuals. Treatment success was assessed in terms of benefit per R (BPR), the ratio of average benefit in weight gain to change in frequency of resistance alleles R (relative to an untreated population). The optimal indicator in terms of BPR for fixed percentages of calves treated was plasma pepsinogen and the worst ADG; in the latter case treatment was applied to some individuals who were not in need of treatment. The reverse was found when calves were treated according to threshold criteria, with ADG being the best target indicator for treatment. This was also the most beneficial strategy overall, with a significantly higher BPR value than any other strategy, but its degree of success depended on the chosen threshold of the indicator. The study shows strong support for TST, with all strategies showing improvements on calves treated selectively, compared with whole-herd treatment at 3, 8, 13 weeks post-turnout. The developed model appeared capable of assessing the consequences of other TST strategies on calf populations.

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Section: Methodsmentioning

confidence: 99%

Modelling the consequences of targeted selective treatment strategies on performance and emergence of anthelmintic resistance amongst grazing calves

Berk

Laurenson

Forbes

et al. 2016

International Journal for Parasitology: Drugs and Drug Resistan

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“…For instance, during the recent EU FP7 GLOWORM project (www.gloworm.eu), the development of several decision support tools was initiated. These included tools to predict the transmission risk of parasites on pasture (Rose et al, 2015;Verschave et al, 2014), the economic impact at herd level of helminth infections or anthelmintic treatment strategies (Charlier et al, 2012a,b) or anthelmintic efficacy based on faecal egg count reduction (Torgerson et al, 2014). However, there are some critical factors that need to be further looked at in the development of successful decision support tools: perceived usefulness, accessibility, flexibility, credibility, maintenance and adaptability (McCown, 2002).…”

Section: Decision Support Toolsmentioning

confidence: 99%

ECONOHEALTH: Placing helminth infections of livestock in an economic and social context

Charlier

Velde

Voort³

et al. 2015

Veterinary Parasitology

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“…Robust and average values for these traits are lacking, despite an extensive body of literature available on the subject. Recent systematic reviews and meta-analyses have been published to build knowledge of these parameters in other important gastrointestinal parasites such as Cooperia oncophora and Ostertagia ostertagi [16, 17] and Teladorsagia circumcincta [18]. Yet, despite the comprehensive literature available tackling the life-cycle of H. contortus [1], including both the free-living (eggs to infective larvae) and parasitic stages (infective larvae to reproductive adult worms), a quantitative assessment of H. contortu s population dynamics and ecology is still missing.…”

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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The parasitic phase of Ostertagia ostertagi: quantification of the main life history traits through systematic review and meta-analysis

Cited by 25 publications

References 84 publications

Modelling the consequences of targeted selective treatment strategies on performance and emergence of anthelmintic resistance amongst grazing calves

Modelling the consequences of targeted selective treatment strategies on performance and emergence of anthelmintic resistance amongst grazing calves

ECONOHEALTH: Placing helminth infections of livestock in an economic and social context

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

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