The Epidemiology and Control of Some Nematode Infections of Grazing Animals

Jf, Michel

doi:10.1016/s0065-308x(08)60436-4

Cited by 137 publications

(23 citation statements)

References 106 publications

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“…The average generation length for the worm population was 45 days. Hence one year (or 100 days of simulation) is equivalent to 2.2 worm generations, in accordance with field observations [15,16]. These results indicate that our model adequately captured the key epidemiological characteristics of worm infections that we aimed to include in our model.…”

Section: Resultssupporting

confidence: 86%

Adaptation of gastrointestinal nematode parasites to host genotype: single locus simulation models

2013

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BackgroundBreeding livestock for improved resistance to disease is an increasingly important selection goal. However, the risk of pathogens adapting to livestock bred for improved disease resistance is difficult to quantify. Here, we explore the possibility of gastrointestinal worms adapting to sheep bred for low faecal worm egg count using computer simulation. Our model assumes sheep and worm genotypes interact at a single locus, such that the effect of an A allele in sheep is dependent on worm genotype, and the B allele in worms is favourable for parasitizing the A allele sheep but may increase mortality on pasture. We describe the requirements for adaptation and test if worm adaptation (1) is slowed by non-genetic features of worm infections and (2) can occur with little observable change in faecal worm egg count.ResultsAdaptation in worms was found to be primarily influenced by overall worm fitness, viz. the balance between the advantage of the B allele during the parasitic stage in sheep and its disadvantage on pasture. Genetic variation at the interacting locus in worms could be from de novo or segregating mutations, but de novo mutations are rare and segregating mutations are likely constrained to have (near) neutral effects on worm fitness. Most other aspects of the worm infection we modelled did not affect the outcomes. However, the host-controlled mechanism to reduce faecal worm egg count by lowering worm fecundity reduced the selection pressure on worms to adapt compared to other mechanisms, such as increasing worm mortality. Temporal changes in worm egg count were unreliable for detecting adaptation, despite the steady environment assumed in the simulations.ConclusionsAdaptation of worms to sheep selected for low faecal worm egg count requires an allele segregating in worms that is favourable in animals with improved resistance but less favourable in other animals. Obtaining alleles with this specific property seems unlikely. With support from experimental data, we conclude that selection for low faecal worm egg count should be stable over a short time frame (e.g. 20 years). We are further exploring model outcomes with multiple loci and comparing outcomes to other control strategies.

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Section: Resultssupporting

confidence: 86%

Adaptation of gastrointestinal nematode parasites to host genotype: single locus simulation models

2013

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“…The relaxation of acquired immunity to nematodes around host parturition and its consequences on the epidemiology of these parasitic infections of the digestive tract have been largely documented in sheep (see reviews by Armour 1980;Michel 1976;Barger 1993;Gibbs 1986). In contrast, the phenomenon has received little attention in goats, where information is scarce.…”

Section: Introductionmentioning

confidence: 99%

Periparturient rise in fecal egg counts associated with prolactin concentration increase in French Alpine dairy goats

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Hoste

Bouquet

et al. 1998

Parasitology Research

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Previous data on periparturient relaxation of immunity during gastrointestinal nematode infection in goats are scarce and conflicting; one study carried out in fiber (Angora) goats showed a positive association of fecal egg counts with prolactin concentrations around parturition, whereas the two other available studies dealing with dairy goats, gave divergent results. The objectives of the study were thus to assess the occurrence of a periparturient rise in fecal egg counts in dairy goats and to examine a possible relationship between the level of milk production and the intensity of the periparturient rise. A total of 28 French Alpine grazing dairy goats naturally infected with Teladorsagia, Trichostrongylus, and Oesophagostomum were allocated into two groups according to their reproductive status; group 1 (n = 7) consisted of nonpregnant lactating animals in the 3rd month of lactation, whereas group 2 (n = 21) was composed of dry goats at 6 weeks before term. Fecal egg counts, pepsinogen and phosphate blood concentrations, blood eosinophil counts, and prolactin concentrations were individually monitored at weekly intervals for 12 weeks (from midwinter to early spring). The mean fecal egg counts were significantly higher in pregnant goats during the 2 weeks before (668 versus 242 eggs per gram of feces (epg), P < 0.05) and the 2 weeks after (962 versus 279 epg, P < 0.01) parturition as compared with nonpregnant lactating animals. No significant difference was seen in the composition of larval cultures between the two groups of animals, with Oesophagostomum infective larvae being found predominantly, particularly at the time of parturition. Pepsinogen and phosphate concentrations as well as blood eosinophil counts were similar between the two groups throughout the survey and indicated a moderate larval challenge. The mean prolactin concentration measured in pregnant goats was significantly higher (P < 0.01) at the time of parturition (298 versus 130 ng ml(-1)) and at 4 weeks after parturition (387 versus 193 ng ml(-1)) than that determined in nonpregnant animals. Furthermore, a significant correlation (rs = 0.30, df = 79; P < 0.01) between fecal egg counts and prolactin concentrations was recorded for the pregnant goats during the 4-weeks period around parturition.

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“…Of these, 32% (29) indicated that the anthelmintic they would use would be a different product to that used for the flock in the current year. The majority of respondents (71% [20]) treated with a macrocyclic lactone.…”

Section: Resultsmentioning

confidence: 99%

“…In the past 'drench/treat and move' to 'safe' pasture was a globally recommended parasite control practice for lambs [3,20] which, providing drug efficacy was high, ensured that 'safe' pasture maintained this minimally contaminated status for a longer period thus negating the need for frequent treatment of young livestock. Van Wyk [3] has questioned the wisdom of this system, indicating that it can hasten the development of resistance as the anthelmintic resistant worms, that have survived treatment, will be the dominant contributor to the population on the 'safe' pasture.…”

Section: Discussionmentioning

confidence: 99%

Gastrointestinal nematode control practices on lowland sheep farms in Ireland with reference to selection for anthelmintic resistance

et al. 2011

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Gastrointestinal parasitism is a widely recognised problem in sheep production, particularly for lambs. While anthelmintics have a pivotal role in controlling the effects of parasites, there is a paucity of data on how farmers use anthelmintics. A representative sample of Irish lowland farmers were surveyed regarding their parasite control practices and risk factors that may contribute to the development of anthelmintic resistance. Questionnaires were distributed to 166 lowland Irish sheep producers. The vast majority of respondents treated their sheep with anthelmintics. Lambs were the cohort treated most frequently, the majority of farmers followed a set programme as opposed to treating at sign of disease. A substantial proportion (61%) administered four or more treatments to lambs in a 'normal' year. Departures from best practice in anthelmintic administration that would encourage the development of anthelmintic resistance were observed. In conclusion, in the light of anthelmintic resistance, there is a need for a greater awareness of the principles that underpin the sustainable use of anthelmintics and practices that preserve anthelmintic efficacy should be given a very high priority in the design of helminth control programmes on each farm. To this end, given that veterinary practitioners and agricultural advisors were considered to be the farmer's most popular information resource, the capacity of these professions to communicate information relating to best practice in parasite control should be targeted.

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The Epidemiology and Control of Some Nematode Infections of Grazing Animals

Cited by 137 publications

References 106 publications

Adaptation of gastrointestinal nematode parasites to host genotype: single locus simulation models

Adaptation of gastrointestinal nematode parasites to host genotype: single locus simulation models

Periparturient rise in fecal egg counts associated with prolactin concentration increase in French Alpine dairy goats

Gastrointestinal nematode control practices on lowland sheep farms in Ireland with reference to selection for anthelmintic resistance

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