Reduced egg shedding in nematode-resistant ewes and projected epidemiological benefits under climate change

Vineer, Hannah Rose; Baber, Peter; White, Thomas A.; Morgan, Eric R.

doi:10.1016/j.ijpara.2019.06.008

Cited by 12 publications

(9 citation statements)

References 38 publications

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“…in particular are more fecund than most other trichostrongylid species [14]. Another factor involved in fecundity is the host itself, since immunity, health and genetics can strongly influence the number of eggs shed by intestinal worms [26]. In addition, samples in which Trichostrongylus dominated were collected in November/December, whereas those samples in which Haemonchus was present were mostly collected in September and October.…”

Section: Discussion Anthelmintic Resistance On the Farms Examinedmentioning

confidence: 99%

Multispecific resistance of sheep trichostrongylids in Austria

et al. 2021

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Anthelmintic overuse and failure to implement methods preventing the development and spread of anthelmintic resistance (AR) have led to an alarming increase of resistant ovine trichostrongylids worldwide. The aim of the present study was to determine whether the routine anthelmintic treatment strategy was effective, to obtain insights into the frequency of AR in trichostrongylids of sheep in Austria, and to determine the presence of different trichostrongylid genera. On 30 sheep farms, the faecal egg count reduction test (FECRT) was performed with the Mini-FLOTAC technique in two consecutive studies. In study 1, only fenbendazole and moxidectin were tested, while different compounds and products were used in study 2. Overall, 33 treatment groups were formed: 11 groups were treated with benzimidazoles (fenbendazole and albendazole), 2 groups with avermectins (ivermectin, doramectin), 18 groups with moxidectin, and two groups with monepantel. Reduced efficacy was detected in 64%, 100%, 28% and 50% of these groups, respectively. The most frequently detected genus in larval cultures was Haemonchus, which had been barely detected in Austria previously, followed by Trichostrongylus. Multispecific resistance of trichostrongylids in Austria seems to be on the rise and H. contortus was detected unexpectedly frequently in comparison to previous studies. There is an urgent need to develop efficient communication strategies aimed at improving the engagement of farmers and veterinarians in sustainable parasite control.

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Section: Discussion Anthelmintic Resistance On the Farms Examinedmentioning

confidence: 99%

Multispecific resistance of sheep trichostrongylids in Austria

et al. 2021

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“…There is also evidence that heritable resistance can be selected (e.g. Rose Vineer et al ., 2019, for gastrointestinal nematodes in sheep). Monogenean infections on fish show equivalent characteristics of heritability of resistance (e.g.…”

Section: Discussionmentioning

confidence: 99%

Heterogeneity in helminth infections: factors influencing aggregation in a simple host–parasite system

et al. 2019

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The almost universally-occurring aggregated distributions of helminth burdens in host populations have major significance for parasite population ecology and evolutionary biology, but the mechanisms generating heterogeneity remain poorly understood. For the direct life cycle monogenean Discocotyle sagittata infecting rainbow trout, Oncorhynchus mykiss, variables potentially influencing aggregation can be analysed individually. This study was based at a fish farm where every host individual becomes infected by D. sagittata during each annual transmission period. Worm burdens were examined in one trout population maintained in isolation for 9 years, exposed to self-contained transmission. After this year-on-year recruitment, prevalence was 100% with intensities 10–2628, mean 576, worms per host. Parasite distribution, amongst hosts with the same age and environmental experience, was highly aggregated with variance to mean ratio 834 and negative binomial parameter, k, 0.64. The most heavily infected 20% of fish carried around 80% of the total adult parasite population. Aggregation develops within the first weeks post-infection; hosts typically carried intensities of successive age-specific cohorts that were consistent for that individual, such that heavily-infected individuals carried high numbers of all parasite age classes. Results suggest that host factors alone, operating post-infection, are sufficient to generate strongly overdispersed parasite distributions, rather than heterogeneity in exposure and initial invasion.

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“…Including an untreated control group in FECRT [ 16 ] allows non-therapeutic reduction in FEC to be accounted for, but is not always practical on farms [ 8 ]. Similarly, measurement of AE in sheep ewes during early lactation is tempting due to high FEC at this time [ 77 ], but is confounded by acute temporary loss of immunity during the peri-parturient rise and its rapid re-instatement.…”

Section: Host Confoundersmentioning

confidence: 99%

Confounding factors affecting faecal egg count reduction as a measure of anthelmintic efficacy

et al. 2022

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Increasing anthelmintic resistance (AR) in livestock has stimulated growing efforts to monitor anthelmintic effectiveness (AE) on livestock farms. On-farm assessment of AE relies on measuring the reduction in faecal egg count (FEC) following treatment; and if conducted rigorously, qualifies as a formal FEC reduction test (FECRT) for AR. Substantial research effort has been devoted to designing robust protocols for the FECRT and its statistical interpretation; however, a wide range of factors other than AR can affect FEC reduction on farms. These are not always possible to control, and can affect the outcome and repeatability of AE measurements and confound the on-farm classification of AR using FECRT. This review considers confounders of FEC reduction, focusing on gastrointestinal nematodes of ruminants, including host and parasite physiology and demography; pharmacokinetic variation between drugs, parasites and hosts; and technical performance. Drug formulation and delivery, host condition and diet, and seasonal variation in parasite species composition, can all affect AE and hence observed FEC reduction. Causes of variation in FEC reduction should be attenuated, but this is not always possible. Regular monitoring of AE can indicate a need to improve anthelmintic administration practices, and detect AR early in its progression. Careful interpretation of FEC reduction, however, taking into account possible confounders, is essential before attributing reduced FEC reduction to AR. Understanding of confounders of FEC reduction will complement advances in FECRT design and interpretation to provide measures of anthelmintic efficacy that are both rigorous and accessible.

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Reduced egg shedding in nematode-resistant ewes and projected epidemiological benefits under climate change

Abstract: Graphical abstract

Cited by 12 publications

References 38 publications

Multispecific resistance of sheep trichostrongylids in Austria

Multispecific resistance of sheep trichostrongylids in Austria

Heterogeneity in helminth infections: factors influencing aggregation in a simple host–parasite system

Confounding factors affecting faecal egg count reduction as a measure of anthelmintic efficacy

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