Observations on the epidemiology of autumn nematodirosis in weaned lambs in a Scottish sheep flock

Sargison, Neil; Wilson, David J.; Scott, Phil

doi:10.1136/vr.100145

Cited by 17 publications

(12 citation statements)

References 31 publications

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“…Hatching in the absence of a chill has been previously documented, albeit at low levels, both historically [2,4,14] and more recently [6,7,15]. Previous studies of non-chilled hatching in N. battus highlighted variability between farm populations [3,7], consistent with the present findings.…”

Section: Discussionsupporting

confidence: 90%

Variation in hatching responses of Nematodirus battus eggs to temperature experiences

et al. 2020

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Background Nematodirus battus, unlike most other gastrointestinal nematodes, undergoes maturation to an infective larva within the egg. Historically, eggs were considered to require a period of chilling over winter followed by a period of temperature above 10 °C for synchronous hatching to occur (generally in spring). Anecdotal reports of Nematodirus infection out-with spring in veterinary journals and the farming press suggest that the concentrated pasture abundance of N. battus infective larvae may be changing. In order for control practices to be adapted, and unexpected disease outbreaks to be avoided, it is important to quantify how parasite epidemiology is changing and research the drivers behind it. Method The present study investigated the in vitro hatching response to temperature experiences (with and without a period of chilling) for egg samples of 90 N. battus populations obtained from 73 commercial sheep farms. Six aliquots of larvated eggs were prepared per population, three aliquots were placed at 4 °C for 6 weeks to provide a chill stimulus then incubated at the optimal hatching temperature for the species. The remaining three aliquots of eggs were incubated at the hatching temperature without a prior chill stimulus and the number of hatched larvae was compared between treatments. Results Median hatch rate across all populations with chilling was 45% (95% CI: 42–48%) and without chilling was 4% (95% CI: 2–6%). Inter-population variation in hatching ranged from 0 to 87% of eggs able to hatch in the absence of a chill stimulus, mean non-chill hatching was 13 ± 2% of eggs (mean ± SE). Non-chill hatching rates were greater than chilled hatching rates in seven of the 90 populations tested. Conclusions Clearly, the variation in hatching responses to temperature experience is very large and therefore the seasonality of the parasite may vary not only between regions but also at farm level. In contrast to what previous work has suggested, there was a geographical trend towards higher non-chill hatching in the Northern parts of the UK.

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Section: Discussionsupporting

confidence: 90%

Variation in hatching responses of Nematodirus battus eggs to temperature experiences

et al. 2020

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“…The gastrointestinal nematodes (GIN), especially the species Haemonchus contortus, are highly prevalent parasites in small ruminants; also, they are responsible for large economic losses in livestock (Sargison et al, 2012). The GIN infections results in anemia, submandibular edema, weight loss, decrease in milk production, lethargy and increased death rate (Molento et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

In vitro anthelmintic activity of the Zizyphus joazeiro bark against gastrointestinal nematodes of goats and its cytotoxicity on Vero cells

Gomes

Lima

Vaz

et al. 2016

Veterinary Parasitology

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“…While at first glance it would appear that there are a high number of holdings in NI where reduced drug efficacy is a problem, this may not in fact be the case. The five classes of anthelmintics claim efficacy against N. battus [ 55 ], although the parasite is a dose-limiting species for mebendazole (and other early, insoluble BZs) [ 27 ] and for most of the ML anthelmintics [ 37 ]. Reduced BZ activity was present in 35.7% of flocks tested with BZs.…”

Section: Discussionmentioning

confidence: 99%

“…It has been shown that up to ~70% of all deposited eggs will hatch without the chilling stimulus [ 19 ] and it has been suggested that the phenotypic plasticity in N. battus hatching behaviour represents a “bet-hedging” strategy that allows the establishment of “chilled” larvae in parasite-naïve lambs, supplemented by infection later in the season by larvae produced from “non-chilled” eggs [ 20 ]. In recent years, increasingly, outbreaks of nematodirosis have been seen later in the grazing season (or indeed in the Autumn) in older lambs [ 20 – 27 ]. This has already been reported for NI [ 4 ].…”

Section: Introductionmentioning

confidence: 99%

Control of Nematodirus spp. infection by sheep flock owners in Northern Ireland

et al. 2017

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BackgroundTo address a lack of information on the control of ovine helminth parasites in Northern Ireland (NI), a number of research projects have been undertaken, dealing with gastrointestinal nematodes, tapeworms and liver fluke. This investigation concerns Nematodirus and concentrates on three aspects of disease: farm management strategies for its control, derived from the results of a Questionnaire; the efficacy of treatment used by farmers, as determined by a coprological survey; and the hatching requirements of Nematodirus eggs, that is, whether prolonged chilling is a pre-requisite for hatching.ResultsA Questionnaire was sent to 252 sheep farmers in NI in March 2012 (covering the years 2009–2012) and replies were received from 228 farmers. Under-dosing, inaccurate calibration of equipment and inappropriate product choice were poor practices identified. Following this survey, the efficacy of treatment of Nematodirus spp. in sheep flocks was evaluated in April and May 2012. Sampling kits were sent to 51 flock owners, all of whom returned pre- and post-anthelmintic dosing faecal samples to the laboratory for analysis. At the time of treatment, 41 flocks were positive for Nematodirus (as diagnosed by the presence of eggs). Reduced benzimidazole efficacy was detected in 35.7% of flocks tested (n = 28). Although only involving a small number of flocks, reduced efficacy of levamisole treatment was detected in 50%, of avermectins in 33% and of moxidectin in 75% of flocks tested (n = 2, 6 and 4, respectively). In the egg hatch experiment, carried out under “chilled” and “non-chilled” conditions, 43% of the eggs in the “non-chilled” group were able to hatch, compared to 100% in the “chilled” group.ConclusionsThe identification of inefficient control strategies argues for continued education of stockholders, in order to improve their management programmes. This is particularly important where the practices might impact on the development of anthelmintic resistance, which has been shown to exist on NI farms. The appropriate choice of anthelmintic is a vital part of this plan. The ability of eggs to hatch under non-chilled conditions demonstrates a flexibility in hatching behaviour. This may represent an adaptation to climate change and account for the recent emergence of a second, autumnal peak of infection.

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Observations on the epidemiology of autumn nematodirosis in weaned lambs in a Scottish sheep flock

Cited by 17 publications

References 31 publications

Variation in hatching responses of Nematodirus battus eggs to temperature experiences

Variation in hatching responses of Nematodirus battus eggs to temperature experiences

In vitro anthelmintic activity of the Zizyphus joazeiro bark against gastrointestinal nematodes of goats and its cytotoxicity on Vero cells

Control of Nematodirus spp. infection by sheep flock owners in Northern Ireland

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