Gastrointestinal Nematode Parasites Research Articles

Influence of periparturient nutritional demand on resistance to parasites in livestock

Periparturient relaxation of immunity (PPRI) to gastrointestinal nematode parasites may have a nutritional basis, as the increasing nutrient demand at times of nutrient scarcity during late pregnancy and subsequent lactation may result in a penalty on expression of acquired immunity to parasites. This nutritional basis implies that lowering nutritional demand, at constant nutrient supply, should reduce the degree of PPRI. Evidence to support the latter is reviewed through exploration of the effects of reproductive effort on periparturient resistance to parasites. A large body of evidence shows that a lower nutritional demand arising from rearing single rather than multiple lambs and/or kids consistently reduces the degree of PPRI in small ruminants, as manifested by reduced worm burdens and/or nematode egg excretions. Such variation in reproductive effort may also account, at least to some extent, for the often observed between-breed differences in PPRI, which may arise from differences in production potential, and thus nutritional demand. A reduction in nutrient demand can reduce the degree of PPRI in a matter of days. However, host immune responses associated with this nutritional sensitivity of host resistance remain to be elucidated, which may be achieved through a recently established periparturient rodent model.

P-glycoprotein-like protein, a possible genetic marker for ivermectin resistance selection in Onchocerca volvulus

Ivermectin (IVM) is the only safe drug for mass-treatment of onchocerciasis. IVM resistance has been reported in gastrointestinal nematode parasites of animals. A reduction in response to IVM in Onchocerca volvulus could have significant consequences for the onchocerciasis control programs. We have found evidence that, in O. volvulus, repeated IVM treatment selects for specific alleles, of P-glycoprotein-like protein ( PLP), a half-sized ABC transporter. In this study, O. volvulus samples were derived from a clinical trial in Cameroon, in which patients were sampled before, and following 3 years (1994–1997) of IVM treatments. There were four treatment groups: 150 μg/kg (1 × p.a. or 4 × p.a.) and 800 μg/kg (1 × p.a. or 4 × p.a.). DNA of O. volvulus macrofilariae was genotyped over a 476 bp region of the PLP gene and at two control genes. Of the six polymorphic positions found in the PLP amplicon, three of them showed significant selection after 4 × p.a. treatment with IVM (total of 13 IVM treatments) in female worms, and one of the same single nucleotide polymorphisms (SNPs) showed significant selection in the male worms. One of the selected SNPs in the female worms caused an amino acid coding change in the putative protein sequence. We found a clear selection of some genotypes, a high SNPs association and a loss of polymorphism following 4 × p.a. treatment with IVM. These PLP SNPs and genotypes could be useful markers to follow selection for IVM resistance in the field.

Prenatal toxicity of Ascaris pepsin inhibitor in mice

The developmental toxicity of pepsin inhibitor isolated from Ascaris suum, a gastrointestinal nematode parasite, was evaluated. An embryo–fetal development study was conducted in BALB/c mice. Groups of 21 mated females were treated by intraperitoneal injection (0.3 ml/30 g body weight) with 0.9% NaCl solution vehicle or isolated Ascaris pepsin inhibitor (API) at dose levels of 50, 100, 150 or 200 mg/kg body weight/day on gestation days (GD) 6–15. Maternal food consumption, body weight, and clinical signs were monitored throughout gestation. Cesarean sections were performed on GD 18 and gravid uterine weight, implantation sites, early and late resorptions, live and dead fetuses were collected. Live fetuses were weighed and examined for external, visceral and skeletal variations and malformations. Maternal body weight gain, gravid uterine weight, food consumption were significantly decreased after injection of higher doses of API (100–200 mg/kg/day). All doses of API exhibited an embryotoxic effect (high rate of intrauterine resorption). The percentage of postimplantation loss in the groups with administered API was higher (over 4–11 times) than that in control group. Fetotoxicity was observed in all treatment groups in a dose-related manner and it was evidenced by increased dead fetuses, decreased fetal weight, increased visceral variations and reduced skeletal ossification. Fetal hydronephrosis and internal hydrocephalus were noted at 150, and 200 mg/kg/day. In summary, the maternal toxicity no-observed-adverse-effect level (NOAEL) was 50 mg/kg/day and the low-observed-adverse-effect level (LOAEL) was 100 mg/kg/day under the conditions of this study. However, the developmental toxicity LOAEL was 50 mg/kg/day based on decreased fetal body weight and prenatal mortality.

Feeding Acacia cyanophylla Lindl. foliage to Barbarine lambs with or without PEG: Effect on the excretion of gastro-intestinal nematode eggs

We investigated the potential use of Acacia cyanophylla Lindl. foliage (Acacia), a tanniniferous legume shrub, as biological way to control gastro-intestinal nematode parasitism in sheep. Fourteen Barbarine lambs (12–14 months old, average LW 33.0 ± 4.1 kg) that had not been treated with anthelmintics for at least the last 6 months were housed in individual pens. Seven animals were allocated to control and experimental groups according to their individual faecal egg counts (FECs) and live weight. Dietary treatments were evaluated during four consecutive periods; Period 1 (days 7–22), Period 2 (days 23–48), Period 3 (days 49–69) and Period 4 (days 70–97). Individuals in both groups received roughage ad libitum and 300 g concentrate throughout the trial. The control lambs were given oaten hay and 50 g polyethylene glycol (PEG, molecular weight 4000) was added to the concentrate in Period 4. The roughage given to the experimental group comprised oaten hay in Periods 1 and 4 and fresh (frozen) Acacia in Periods 2 and 3. PEG was included in concentrate during Period 3. Acacia foliage contained about 140 g crude protein/kg DM, condensed tannins (CT, ca. 82 g leucocyanidin equivalents/kg DM). Faecal egg counts were made on samples taken from the rectum of the lambs at the day of transfer from the field station (day 0), then twice a week throughout the experiment. Generic composition of the nematode population was determined by coproculture. In control lambs, the FECs and total egg counts (TECs; daily egg production) were unchanged over the four measurement periods (P>0.05). In the experimental animals, Acacia given in Period 2 decreased FEC (P<0.05) and TECs (P<0.001). Inclusion of PEG with Acacia in Period 3 increased TECs (P<0.01), suggesting the CT were associated with antiparasitic activity. Six nematode genera were identified by coproculture during the four periods and proportions of each genera were similar in control and experimental groups during all experimental periods. This experiment confirmed the antiparasitic activity of Acacia foliage is likely to be due to the Acacia CT.

Sheep and cattle grazing alternately: Nematode parasitism and pasture decontamination

Three grazing management systems were compared to examine pasture decontamination of gastrointestinal nematode parasites (GIN) of sheep ( Ovies aries) and cattle ( Bos taurus). They consisted of sheep and cattle grazing paddocks alternately for 32, 96 or 192 days over 2 years. Pastureland (8.43 ha) was subdivided into six areas of eight paddocks each to produce an eight-paddock rotational grazing system. Every paddock was grazed for 4 days and then rested for 28 days. Sixty-six Ile de France ewes and 12 steers were randomly divided into three groups (22 sheep and four cattle per group). Each grazing system included a cattle area and a sheep area. Sheep and cattle interchanged areas every 32 days in system 1 (Group 1), every 96 days in system 2 (Group 2) and every 192 days in system 3 (Group 3). Fecal examination and larvae counting on pasture were performed every 32 days. During summer, winter and spring 2005, tracer lambs free of nematode infection were introduced into each sheep group and later sacrificed for quantification and identification of GIN species. All cattle were sacrificed for the same purpose. The main parasites found in tracer lambs were Haemonchus contortus and Trichostrongylus colubriformis, and in cattle, Haemonchus similis, Cooperia punctata and Oesophagostomum radiatum. Pasture contamination by sheep-infective GIN larvae was considerably reduced after 96 or 192 days of cattle grazing. Cross-infections between sheep and cattle GIN were not significant, which suggested that integrated grazing using such animals could be used for pasture decontamination. However, as effective anthelmintics were not available, decontamination was not sufficient for proper prophylaxis of GIN infections in Ile de France sheep, which are quite susceptible to such parasites.

Management of gastrointestinal nematode parasites on sheep farms in New Zealand

AIM: To report current farmer opinions and farming practices relating to control of gastrointestinal nematodes and anthelmintic resistance on sheep farms in New Zealand. METHODS: An interview-based cross-sectional study of grazing management and anthelmintic useage was conducted by veterinarians on 80 randomly selected sheep farms in New Zealand. RESULTS: Useable data were returned by 74/80 (92%) farmers who participated in the study. However, despite contacting 400 farmers the target sample size of 100 farms was not reached. The results indicated that only 31% of farms had previously tested for drench resistance, that effective quarantine-drenching of imported stock was not always carried out, and that farmers were more likely to integrate cattle than ewes into their grazing management of lambs. Furthermore, the number of drenches given to lambs had changed little in 25 years. The use of faecal egg counting by farmers has increased. CONCLUSIONS: Dependence on anthelmintics continues to be high on sheep farms in New Zealand. Whilst the number of drench treatments has changed little, there is more widespread use of persistent or long-acting treatments. Farmers need to be encouraged to monitor the resistance status of nematode populations on their farms and use this information to develop strategies aimed at maintaining susceptible alleles within the parasite populations and conserving the efficacy of existing drug families.

Epidemiological studies of parasitic gastrointestinal nematodes, cestodes and coccidia infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe

Between January 1999 and December 2000 faecal samples from 16264 cattle at 12 dipping sites in the highveld and nine in the lowveld communal grazing areas of Zimbabwe were examined for gastrointestinal (GI) nematode and cestodes eggs, and coccidia oocysts. Strongyle larvae were identified following culture of pooled faecal samples collected at monthly intervals. The effects of region, age, sex and season on the prevalence of GI nematodes, cestodes and coccidia were determined. Faecal egg and oocyst counts showed an overall prevalence of GI nematodes of 43%, coccidia 19.8% and cestodes 4.8%. A significantly higher prevalence of infection with GI nematodes, cestodes and coccidia was recorded in calves (P < 0.01) than in adults. Pregnant and lactating cows had significantly higher prevalences than bulls, oxen and non-lactating (dry cows) (P < 0.01). The general trend of eggs per gram (epg) of faeces and oocysts per gram (opg) of faeces was associated with the rainfall pattern in the two regions, with high epg and opg being recorded during the wet months. The most prevalent genera of GI nematodes were Cooperia, Haemonchus and Trichostrongylus in that order. Strongyloides papillosus was found exclusively in calves. Haemonchus was significantly more prevalent during the wet season than the dry season (P < 0.01). In contrast, Trichostrongylus was present in significantly (P < 0.01) higher numbers during the dry months than the wet months, while Cooperia and Oesophagostomum revealed no significant differences between the wet and dry season. These findings are discussed with reference to their relevance for strategic control of GI parasites in cattle in communal grazing areas of Zimbabwe.

Markers for benzimidazole resistance in human parasitic nematodes?

Benzimidazole (BZ) resistance is widespread and appears to be readily selected in a variety of nematode parasites of animals. There have been reports of a lack of efficacy of BZ anthelmintics against soil transmitted nematode parasites of humans. However, resistance to BZs in nematodes of humans has not been confirmed. It is difficult to perform tests to confirm anthelmintic resistance in humans for a variety of technical and ethical reasons. The use of anthelmintic drugs for the control of helminth parasites in people is increasing massively as a result of numerous programmes to control gastrointestinal nematode parasites in children, the Global Program for the Elimination of Lymphatic Filariasis and other programmes. Many of these programmes are dependent on BZ anthelmintics and this will increase the pressure for resistance development to BZ anthelmintics in nematode parasites of people. We need to perform monitoring for anthelmintic resistance in these programmes and we need new tools to make that monitoring sensitive, inexpensive and practical. There is a real need for DNA-based markers for BZ resistance in nematode parasites of humans. We have a reasonable understanding of the molecular mechanisms and genetics of BZ resistance in some nematode parasites of animals and similar mechanisms are likely to prevail in nematodes of humans. Based on the likelihood that similar single nucleotide polymorphisms (SNPs) will be involved in BZ resistance in human, as in animal nematode parasites, rapid SNP assays have been developed for possible BZ resistance development in Wuchereria bancrofti.

Cover Picture: Expansion and activation of CD4+CD25+ regulatory T cells in Heligmosomoides polygyrus infection – Eur. J. Immunol. 7/2007

AbstractThe cover shows a photograph of an individual adult Heligmosomoides polygyrus, a gastrointestinal nematode parasite and was provided by Finney et al. (pp. 1874–1886). In this study authors analyse in detail the development and phenotype (CTLA‐4, GITR, CD103) of cells responsible for the suppression of the early Th2 responses during murine H. polygyrus infection. Both CD25+Foxp3+ and CD25+Foxp3‐ subsets are increased during infection but, interestingly, only the latter display significant increases in TGF‐β levels.

Expansion and activation of CD4(+)CD25(+) regulatory T cells in Heligmosomoides polygyrus infection.

Regulatory T cell responses to infectious organisms influence not only immunity and immunopathology, but also responses to bystander antigens. Mice infected with the gastrointestinal nematode parasite Heligmosomoides polygyrus show an early Th2-dominated immune response (days 7–14), but by day 28 a strongly regulatory profile is evident with antigen-specific IL-10 release and elevated frequency of CD4+ T cells bearing surface TGF-β. CD4+CD25+ T cells from infected mice show enhanced capacity to block in vitro effector T cell proliferation. CD4+CD25+ cell numbers expand dramatically during infection, with parallel growth of both CD25+Foxp3+ and CD25+Foxp3– subsets. CTLA-4 and glucocorticoid-induced tolerance-associated receptor, also associated with regulatory T cell function, become more prominent, due to both expanded CD25+ cell numbers and increased expression among the CD25– population. Both intensity and frequency of CD103 expression by CD4+ T cells rise significantly, with greatest expansion among CD25+Foxp3+ cells. While TGF-β expression is observed among both CD25+Foxp3+ and CD25+Foxp3– subsets, it is the latter population which shows higher TGF-β staining following infection. These data demonstrate in a chronic helminth infection that Foxp3+ regulatory T cells are stimulated, increasing CD103 expression in particular, but that significant changes occur to other populations including expansion of CD25+TGF-β+Foxp3– cells, and induction of CTLA-4 on CD25– non-regulatory lymphocytes.

Infection with parasitic nematodes confounds vaccination efficacy

T helper (Th) cells produce signature cytokine patterns, induced largely by intracellular versus extracellular pathogens that provide the cellular and molecular basis for counter regulatory expression of protective immunity during concurrent infections. The production of IL-12 and IFN-γ, for example, resulting from exposure to many bacterial, viral, and protozoan pathogens is responsible for Th1-derived protective responses that also can inhibit development of Th2-cells expressing IL-4-dependent immunity to extracellular helminth parasites and vice versa. In a similar manner, concurrent helminth infection alters optimal vaccine-induced responses in humans and livestock; however, the consequences of this condition have not been adequately studied especially in the context of a challenge infection following vaccination. Demands for new and effective vaccines to control chronic and emerging diseases, and the need for rapid deployment of vaccines for bio security concerns requires a systematic evaluation of confounding factors that limit vaccine efficacy. One common albeit overlooked confounder is the presence of gastrointestinal nematode parasites in populations of humans and livestock targeted for vaccination. This is particularly important in areas of the world were helminth infections are prevalent, but the interplay between parasites and emerging diseases that can be transmitted worldwide make this a global issue. In addition, it is not clear if the epidemic in allergic disease in industrialized countries substitutes for geohelminth infection to interfere with effective vaccination regimens. This presentation will focus on recent vaccination studies in mice experimentally infected with Heligmosomoides polygyrus to model the condition of gastrointestinal parasite infestation in mammalian populations targeted for vaccination. In addition, a large animal vaccination and challenge model against Mycoplasma hyopneumonia in swine exposed to Ascaris suum will provide a specific example of the need for further work in this area, and for controlled field studies to assess the impact of other similar scenarios.

Heritability of resistance to infestation with the body louse, Bovicola ovis, in Romney sheep bred for differences in resistance or resilience to gastro-intestinal nematode parasites

The inheritance of resistance to louse infestation and the related allergic skin disease, cockle, was examined in Romney lambs. The lambs used in the study were the 2001- and 2004-born progeny of four experimental breeding lines (“Resistant”, “Susceptible”, “Resilient” and “Control”) developed as part of a long-term study of the genetics of host resistance (maintenance of low faecal egg count (FEC) under nematode challenge) or resilience (maintenance of health and productivity under nematode challenge irrespective of FEC) to nematode parasites in sheep. Between 13 and 22 progeny (equally distributed between males and females, where possible) from each of five sires in each line were selected each year for this trial. All lambs ( n = 701) were examined for lice ( Bovicola ovis) before artificial infestation; in 2001 the lambs were free of natural infestation, whilst in 2004 naturally acquired infestation was evident. In November 2001 and May 2002, approximately 60 B. ovis were transferred to each lamb, followed by monitoring at approximately 2-monthly intervals until August 2002. Similar procedures, but with fewer monitoring times, were repeated on the 2004 lambs. Overall, lambs in the Control line were significantly more susceptible to louse infestation and cockle compared with those in the other three lines ( P < 0.001). Least squares-means (SEM) of log-transformed louse score for the control, resistant, susceptible and resilient lines, respectively, were 2.178 (0.045), 1.499 (0.050), 1.618 (0.050) and 1.587 (0.044), and for cockle score were 1.36 (0.05), 0.76 (0.05), 0.95 (0.05) and 0.78 (0.05). From all progeny together, the heritability of log-transformed louse score was 0.22 (Standard Error (SE) 0.06) in autumn and 0.34 (SE 0.08) in winter, with a value of 0.44 (SE 0.09) when these data were combined. These estimates were similar to those obtained for resistance to gastro-intestinal nematodes in these breeding lines, using log-transformed FECs. Heritability estimates for cockle score in autumn, winter and when combined were 0.06 (SE 0.04), 0.45 (SE 0.09) and 0.40 (SE 0.09), respectively. The genetic correlations of mean log-transformed louse score with mean cockle score and levels of two different louse antigens in wool were, respectively, 0.97 (SE 0.04), 0.96 (SE 0.08) and 0.95 (SE 0.09). However, there was no significant genetic correlation between louse scores and FEC. These results suggest that selective breeding would be effective in reducing louse infestation and cockle in sheep, but that differences in louse burdens were not related to differences in nematode burdens as indicated by FECs.

Faecal soiling and gastrointestinal helminth infection in lambs

The accumulation of faeces in the wool of the breech area (tail, perineum and anus) of lambs, known as faecal soiling, has been shown to be one of the major factors predisposing sheep to blowfly strike. However, the causes of faecal soiling of lambs in the UK are not clearly understood. Hence, in this investigation, the relationships between faecal soiling, gastrointestinal parasitic nematode infection and resultant diarrhoea were examined in a longitudinal study of 200 lambs at two farms in south-west England. Faecal egg counts, pasture worm burdens, faecal soiling and growth rates were recorded for individually tagged lambs over the summer of 2003. Grass growth and nutritional composition (protein and fibre) and weather data were also recorded over this period. Analysis using linear mixed models showed that faecal soiling was associated with higher strongyle-type egg counts, longer periods since worming, lower live-weights, female gender, lower faecal consistency and pasture quality. The data indicate that dag scoring, especially in mid- to late summer, could be used as a rapid, non-invasive technique for selecting animals, particularly lambs, with high faecal egg counts for selective drenching to reduce the incidence of anthelmintic resistance. Selective drenching of lambs with high dag scores would also be expected to aid in the control of blowfly strike.

Three surface antigens dominate the mucosal antibody response to gastrointestinal L3-stage strongylid nematodes in field immune sheep

Although gastrointestinal nematode parasites are a major human and veterinary health problem, little is known about how the host is sometimes able to mount an effective immune rejection response. In previous work, we identified a carbohydrate larval surface antigen (CarLA) as the target of mucosal antibodies that can elicit rejection of Trichostrongylus colubriformis L3s in sheep. Here we characterise the natural mucosal antibody responses to L3s from three major strongylid gastrointestinal parasites of sheep, Trichostrongylus colubriformis, Haemonchus contortus and Teladorsagia circumcincta. The mucosal antibody repertoire of naturally field-immune sheep was displayed on bacteriophage as single-chain antibodies (scFvs) and phage were selected for the ability to bind to the surface of living L3s of the three nematode species. All nematode-binding scFvs were found to recognize one of three different antigen classes that are each found in the three strongylid species. These three antigen classes appear to represent all of the major antigens recognized on Western blots by pooled mucosal antibodies from field-immune sheep. One of the antigen classes is a heterogeneous, high molecular weight molecule that is protease-sensitive. The scFvs recognizing this surface antigen also recognize a similar antigen in all strongylids tested. A second antigen class is a protease-insensitive, low molecular weight antigen found only in sheaths and scFvs recognizing this antigen cross-react with a similar molecule found in all strongylids tested. The third surface antigen class is CarLA and all of the anti-CarLA scFvs obtained from the field-immune sheep repertoire were specific to L3s of only one species and often recognized only a subset of the worms. Thus three different L3-stage surface antigens, two that lack a protein component, dominate the natural mucosal antibody response to L3-stage gastrointestinal strongylid nematodes in sheep.

Viabilidade de formulação peletizada do fungo nematófago Monacrosporium sinense, no controle biológico de nematóides parasitos gastrintestinais de bezerros

A viabilidade de uma formulação do fungo Monacrosporium sinense foi avaliada no controle de nematóides parasitos gastrintestinais de bovinos. Dois grupos de 10 bezerros cada um, mestiços Holandês x Zebu, de seis a nove meses de idade, foram colocados em pastagem de Brachiaria brizantha. Em um dos grupos, cada animal recebeu 20g de péletes em matriz de alginato de sódio, contendo massa miceliana do fungo M. sinense via oral, duas vezes por semana, durante seis meses, com início no mês de outubro; no outro grupo, controle, os bezerros não receberam esse tratamento. As contagens de ovos por grama de fezes (OPG) e de larvas infectantes por kg de matéria seca foram maiores (P&lt;0,05) no grupo-controle, e a diferença entre o OPG dos dois grupos, no final do experimento, foi de 79%. A viabilidade dos péletes em germinar e a atividade predatória do fungo após o encapsulamento foram avaliadas in vitro. A porcentagem de péletes com cultivo positivo para o fungo variou entre 90 e 100%, e o percentual de redução de larvas infectantes in vitro variou entre 90,6 e 100%. A aplicação de péletes de M. sinense na dosagem e periodicidade usadas são eficazes no biocontrole de nematóides parasitos gastrintestinais de bovinos.

Haemonchus contortus intestine: a prominent source of mucosal antigens

We sought to identify antigens from Haemonchus contortus, an abomasal nematode of small ruminants, that stimulate local (abomasal lymph node, ALN) CD4+ T lymphocyte responses during a primary infection. Results led to a focus on antigens from the parasite intestine. The H. contortus intestine proved to be a major source of antigens that stimulated ALN CD4+, CD25+ T lymphocyte responses during infections in lambs. When stimulated by intestinal antigens, ALN lymphocytes from these lambs expressed IL-4 and IL-13 transcripts, and, more variably, IFN-gamma. An immunoaffinity-purified fraction, enriched for H. contortus apical intestinal membrane proteins, stimulated similar ALN responses. On further fractionation, antigens from six size classes (ranging from 30 to 200 kDa) also stimulated proliferation of ALN lymphocytes. Mass spectrometry analysis of these size classes identified several known apical intestinal membrane proteins from H. contortus. The results show that H. contortus intestinal antigens warrant investigation in strategies to induce mucosal immunity against this parasite. The specific proteins identified have value for this purpose. The results are in contrast with the now generalized idea that H. contortus intestinal antigens are 'hidden' from the host immune system, and this issue is discussed. The approach also has potential application to other gastrointestinal nematode parasites.

Risk factors of gastrointestinal nematode parasite infections in small ruminants kept in smallholder mixed farms in Kenya

BackgroundHelminth infections in small ruminants are serious problems in the developing world, particularly where nutrition and sanitation are poor. This study investigated the burden and risk factors of gastrointestinal nematode parasite infections in sheep and goats kept in smallholder mixed farms in the Kenyan Central Highlands. Three hundred and seven small ruminants were sampled from 66 smallholder mixed farms in agro-ecological zones 1 (humid) and 3 (semi-humid) in the Kenyan Central highlands. The farms were visited once a month for eight months during which a health and production survey questionnaire was administered. Fecal samples were collected at each visit from each animal. Fecal egg counts (FEC) were performed using the modified McMaster technique. Associations between potential risk factors and FEC were assessed using 3-level Poisson models fit in SAS using GLIMMIX macro. Correlations among repeated observations were adjusted for using three different correlation structures.ResultsA rise in FEC was observed two months after the onset of rains. Farmer education, age category, de-worming during the preceding month and grazing system were significant predictors of FEC. Additionally, there were significant interactions between grazing system and both de-worming and age category implying that the effect of grazing system is dependent on both de-worming status and age category; and that the effect of de-worming depends on the grazing system. The most important predictors of FEC in the study area were grazing system, de-worming status and education of the farmers.ConclusionSince several factors were important predictors of FEC, controlling gastrointestinal helminths of small ruminants in these resource-poor smallholder mixed farms requires a sustainable integrated helminth control strategy that includes adoption of zero-grazing and more farmer education probably through extension services. Achieving improved helminth controls in these resource-poor farming systems offers an opportunity to increase small ruminant productivity and hence has a potential of improving the livelihood of the resource-poor farmers.

Substitution of benzimidazole-resistant nematodes for susceptible nematodes in grazing lambs

Multi-drug-resistant gastrointestinal nematode parasite populations are becoming more and more prevalent. Since anthelmintic treatments are of limited effectiveness, one solution could be to replace the anthelmintic-resistant population by a susceptible population, in order to re-establish the possibility of drug-based anthelmintic control. We investigated this substitution strategy in 4 paddocks of 0.7 ha, each of which was seeded with a benzimidazole-resistant Teladorsagia circumcincta population. The proportion of benzimidazole-resistant worms in these paddocks ranged from 20% to 89%. A 2-step replacement was performed: first, the paddocks were not grazed for 6 months (from December to July), and then the grass was cut to eliminate any residual infective larvae, before contaminating each of the paddocks with 10 seeder lambs experimentally infected with a benzimidazole-susceptible strain of T. circumcincta (from July to November). At the end of the experiment, all the populations on the 4 paddocks were phenotypically benzimidazole-susceptible, but genotyping indicated that 2 populations harboured 1% and 3% resistant worms respectively. This study demonstrates that nematode replacement is feasible in temperate areas, using semi-intensive stock management, even when the initial levels of benzimidazole-resistance are very high. Further research should next assess replacing the whole community to cope with the species diversity observed under field conditions.

Gastrointestinal nematode parasites of sheep: A dynamic model for their effect on liveweight gain

This paper presents an individual-based model for gastrointestinal nematode parasites of sheep and includes the effect of these parasites on the liveweight performance of young sheep. Parasitism is known to affect the host animal in at least two ways. The first induces a loss of appetite in the host, which reduces pasture consumption compared with the parasite-free animal. This effect is examined in the first part of the study. The second major effect of parasitism is a reduction in the metabolic efficiency of the host which decreases nutrients available for maintenance and growth. The latter part of the paper examines the consequences of incorporating this effect on the liveweight changes in individuals in a group of sheep. Previous models addressing this issue have only given mean liveweight and worm burden changes.

Biological Control of Gastrointestinal Parasitic Nematodes Using Duddingtonia flagrans in Sheep under Natural Conditions in Mexico

This investigation was aimed to evaluate the use of an oral bio-preparation containing Duddingtonia flagrans chlamydospores for the control of sheep gastrointestinal parasitic nematodes under the Mexican cold high plateau conditions. Two groups of gastrointestinal parasitic nematode naturally infected sheep, were randomly selected and located into two free-gastrointestinal nematode larvae paddocks. Group 1 received once a week a supplement containing D. flagrans chlamydospores mixed with oats and molasses. Group 2 received a similar supplement without any fungal material. After 5 months grazing animals were discarded from the experiment and two groups of free-nematode "tracer" sheep were located into the same paddocks to collect larvae from the contaminated pastures. Animals were slaughtered and necropsied and the nematodes were obtained and counted. A screening of the number of gastrointestinal nematode larvae present on the grass was performed and compared between the two grazing areas. The results showed 56% reduction in the Ostertagia (Teladorsagia) circumcincta and 94% reduction in the Nematodirus sp. population of the "tracer" sheep who grazed on the D. flagrans-treated sheep area, compared to the nematode population in animals grazed on the non-treated area. The results of the number of larvae on the grazing pastures showed a 51.1% reduction for H. contortus, and 100% for Cooperia sp. in the area with fungi. In the case of Trichostrongylus sp. no reduction was observed, when compared to the control group.