Gastrointestinal Nematode Infections In Sheep Research Articles

Identifying hepatic genes regulating the ovine response to gastrointestinal nematodes using RNA-Sequencing.

Gastrointestinal nematode (GIN) infections are considered the most important disease of grazing sheep and due to increasing anthelmintic resistance, chemical control alone is inadequate. Resistance to Gastrointestinal nematode infection is a heritable trait, and through natural selection many sheep breeds have higher resistance. Studying the transcriptome from GIN-exposed and GIN-unexposed sheep using RNA-Sequencing technology can provide measurements of transcript levels associated with the host response to Gastrointestinal nematode infection, and these transcripts may harbor genetic markers that can be used in selective breeding programs to enhance disease resistance. The objective of this study was to compare liver transcriptomes of sheep naturally exposed to Gastrointestinal nematode s, with either high or low parasite burdens, to GIN-unexposed control sheep in order to identify key regulator genes and biological processes associated with Gastrointestinal nematode infection. Differential gene expression analysis revealed no significant differentially expressed genes (DEG) between sheep with a high or low parasite burden (p-value ≤0.01; False Discovery Rate (FDR) ≤ 0.05; and Fold-Change (FC) of > ±2). However, when compared to the control group, low parasite burden sheep showed 146 differentially expressed genes (64 upregulated and 82 downregulated in the low parasite burden group relative to the control), and high parasite burden sheep showed 159 differentially expressed genes (57 upregulated and 102 downregulated in the low parasite burden group relative to the control) (p-value ≤0.01; FDR ≤0.05; and FC of > ±2). Among these two lists of significant differentially expressed genes, 86 differentially expressed genes (34 upregulated, 52 downregulated in the parasited group relative to the control) were found in common between the two parasite burden groups compared to the control (GIN-unexposed sheep). Functional analysis of these significant 86 differentially expressed genes found upregulated genes involved in immune response and downregulated genes involved in lipid metabolism. Results of this study offer insight into the liver transcriptome during natural Gastrointestinal nematode exposure that helps provide a better understanding of the key regulator genes involved in Gastrointestinal nematode infection in sheep.

PSX-B-11 Classification Performance of Multinomial Logistic Regression for Identifying Resistance, Resilience, and Susceptibility to Gastrointestinal Nematode Infections in Sheep

Abstract The objective was to investigate the feasibility of using easy-to-measure phenotypic traits to predict resistant, resilient and susceptible sheep to gastrointestinal nematodes via multinomial logistic regression (MLR). The database comprised 3,654 records on 1,250 Santa Ines sheep from six farms. The animals were classified into three responses to infection classes (resistant, resilient and susceptible) according to fecal egg count and packed cell volume. The MLR was used to predict such classes using the information of age, month of record, sex, Famacha degree, weight and body condition score as predictors, and a leave-one-farm-out cross-validation technique was used to assess prediction quality across farms. The MLR was able to predict with satisfactory performance the resistant and susceptible animals in two of the farms, with resistant precision equal to 79 and 77%, and susceptible recall equal to 68 and 83%, respectively. In addition, at least one of the classes was well predicted in four farms, with susceptible recall equal to 71 and 89% in two of these farms, and resistant precision equal to 86 and 100% in the other two farms. The model was not able to satisfactorily classify resilient class. The proposed approach could help attenuate the negative impacts related to infections caused by gastrointestinal nematodes, contributing to design deworming strategies that take into account the risk of an animal being contaminated, consequently reducing the costs with anthelmintic administration and laboratory analyses based on blood or fecal samples. The results suggest that the use of easily measurable traits may provide useful information for supporting management decisions on the farm level that could potentially contribute to reducing parasitic contamination and production costs. In addition, the animals identified as resistant can also be incorporated as selection candidates into breeding programs for genetic improvement of flocks.Supported by the São Paulo Research Foundation (FAPESP) grants #2020/03575-8, #2018/01540-2 and #2016/14522-7, SP, Brazil.

Blood parameters and immune responses during haemonchosis

Article Details: Received: 2020-10-06 | Accepted: 2020-11-27 | Available online: 2021-01-31 https://doi.org/10.15414/afz.2021.24.mi-prap.29-32 The aim of this experiment was to determine the effect of medicinal plants ( Artemisia absinthium and Malva sylvestris ) as feed supplements on blood parameters, and local immune responses in the abomasum of Haemonchus contortus infected lambs. Twenty-four lambs were infected orally with 5000 L3 larvae of H. contortus and subsequently randomly divided into four groups: unsupplemented animals (UNS), animals with A. absinthium (ART), animals with M. sylvestris (MAL), and animals with a mix of two plants (ARTMAL). During the experiment, samples of blood were taken for evaluation of hemoglobin and albumin levels. All animals were humanely killed after 75 days of the experiment, and abomasum tissue samples were taken for histopathology. The hemoglobin concentration in the blood was influenced by time ( p< 0.001) and in all groups decreased until day 45. The serum albumin levels were influenced by treatment ( p< 0.05) and time ( p< 0.001) and in all groups occurred reduction until the end of the experiment compared to day 15. The number of plasma cells was higher in ARTMAL compared to MAL ( p < 0.05). UNS and ART had significantly higher numbers of mast cells compared to MAL ( p< 0.01 and 0.05, respectively). The regeneration of abomasal tissue was most frequent in ARTMAL. The results showed that dietary supplementation by A. absinthium and M. sylvestris did not positively affected blood parameters but influenced local immune response in the abomasum of H. contortus infected sheep. Keywords: Haemonchus contortus , sheep, hemoglobin, abomasum, local immune response References Besier, R. et al. (2016). The Pathophysiology, Ecology and Epidemiology of Haemonchus contortus. In Gasser, RB and Samson-Himmelstjerna, G. Haemonchus contortus- Past, present and future trends. (1. ed.). London: Elsevier Ltd (pp. 95-143). Hoste, H. et al. (2016). Interactions between nutrition and infections with Haemonchus contortus and related gastrointestinal nematodes in small ruminants. Advances in Parasitology, 93, 239–351. https://doi.org/10.1016/bs.apar.2016.02.025 McRae, KM. et al. (2015). The host immune response to gastrointestinal nematode infection in sheep. Parasite Immunology, 37(12), 605-613. https://doi.org/10.1111/pim.12290. Mravčáková, D. et al. (2019). Natural chemotherapeutic alternatives for controlling of haemonchosis in sheep. BMC Veterinary Research, 15, 1-13. https://doi.org/10.1186/s12917-019-2050-2 Rouatbi, M. et al. (2016). Effect of the infection with the nematode Haemonchus contortus (Strongylida: Trichostrongylidae) on the haematological, biochemical, clinical and reproductive traits in rams. The Onderstepoort Journal of Veterinary Research, 83(1), 1-8. http://dx.doi.org/10.4102/ojvr.v83i1.1129 Váradyová, Z. et al. (2018). Effects of herbal nutraceuticals and/or zinc against Haemonchus contortus in lambs experimentally infected. BMC Veterinary Research, 14(1), 78. https://doi.org/10.1186/s12917-018-1405-4 Villalba, JJ. Et al. (2017). Phytochemicals in animal health: Diet selection and trade-offs between costs and benefits. Proceedings of the Nutrition Society, 76(2), 113-121. https://doi.org/10.1017/S0029665116000719

In Vitro Anthelminthic Efficacy of Aqueous Pomegranate (Punica granatum L.) Extracts against Gastrointestinal Nematodes of Sheep.

The worldwide increased difficulty to counteract gastrointestinal nematode (GIN) infection in sheep, due to progressing anthelmintic resistance, has led to the evaluation of other alternative helminth control options, mainly from plants. The anthelmintic efficacy of an aqueous Punica granatum macerate was evaluated in sheep naturally infected by GIN in southern Italy. The macerate was chemically characterized by chromatographic analysis coupled with high-resolution mass spectrometry (LC/HRMS) and an aliquot was concentrated to obtain a dry extract. A part was characterized, the remaining washed with methanol to obtain an insoluble residue and methanol phase. In the methanol fraction, the quantitatively predominant gallic acid was purified to obtain the pure molecule. The three fractions thus obtained were used for in vitro studies (i.e., egg hatch test) to verify anthelmintic efficacy. For this purpose, fecal samples were collected from sheep naturally infected by GINs. Fractions were diluted in H2O/DMSO 0.5% at 1.00, 0.5, 0.25, 0.125, 0.05, and 0.005 mg/mL concentrations. Thiabendazole (0.25 and 0.5 mg/mL) and deionized water were used as positive and negative controls, respectively. Egg hatch test results indicated that all fractions caused a significant (p < 0.05) egg hatch inhibition within 48 h of exposure highlighting a high (>82%) efficacy in vitro at all tested doses. Maximal egg hatching inhibition effect was exhibited by the methanol fraction (99.3% and 89.3% at 1 and 0.005 mg/mL concentrations), followed by the insoluble residue and gallic acid (94.7% and 85.3% and 94.0% and 82.7% at 1 and 0.005 mg/mL, respectively). The current study validated the anthelmintic potential of traditional P. granatum macerate against GIN infection in sheep, thus highlighting the role of gallic acid as principal component and justifying a need to undertake further in vivo studies on these ethno-veterinary remedies.

129 Evaluation of the effect of Bedoukian compound X administered twice on gastrointestinal nematode infection in sheep

Abstract Gastrointestinal nematodes (GIN) and coccidia have a large financial and health impact on small ruminants. Recent years have seen an increase in anthelminthic/ coccidiostat resistance, and there is a need to develop alternative control methods. The objective of this study was to examine the effect of a unique proprietary compound used in the fragrance/flavor industry with an insect repellant application (Compound X; Bedoukian Research) on parasite control in sheep. Previous research by our laboratories showed a short term reduction in fecal egg count (FEC) in sheep orally drenched with the product. In the current study, naturally infected (GIN and coccidia) Katahdin lambs were orally drenched with 15 mL of Compound X and 15 mL mineral oil (CMX; n = 11) or 30 mL mineral oil (CON; n = 9) on d 0 and 21; FEC/fecal oocyst count (FOC) were determined every 7 d for 8 wk, and feces were cultured to examine GIN larvae. Data were analyzed using a mixed model with repeated measures over time, and regression (SAS). The FEC were reduced in CMX compared with CON between d 0 and 21 (P &lt; 0.03, both mixed model and regression), d 21 and 42 (P &lt; 0.001, mixed and regression), and d 0 and 56 (P &lt; 0.001); FEC were influenced by day of study (P &lt; 0.04), and the interaction tended to be significant using regression (P &lt; 0.10). The FOC were negligible and not analyzed. There was no effect on development of nematode larvae in feces. However, there was a shift in population distribution from Haemonchus contortus to Trichostrongylus spp. which indicated a possible effect on female H. contortus fecundity. There was a sign of toxicity in one lamb following the second CMX drench. The value of using such a compound for GIN control may warrant further investigation.

Planning anthelmintic treatments to control gastrointestinal nematode infections in sheep

A planned approach to anthelmintic treatments against gastrointestinal nematodes in sheep is vital given their clinical and economic importance, and the prevalence of anthelmintic resistance. The key nematode species in the UK are Nematodirus battus, Teladorsagia circumcincta, Trichostrongylus species and Haemonchus contortus. Knowledge of the biology of these species and the annual production cycle on UK sheep farms can guide when treatments may be necessary. The timings of these treatments can be further refined using grazing history, weather conditions and faecal egg counting. This information can then be combined with knowledge of anthelmintic resistance to make a rational treatment decision, and reduce the selection for anthelmintic resistance; for example, by using strategies that maintain populations of parasites in refugia, using multiple active treatments or improving drug bioavailability.

Controlling nematode infections in sheep: application of HACCP

Gastrointestinal nematode infection in sheep is a significant challenge for production with implications for animal health and welfare, and lamb growth. Flocks rely on the chemical control of worm burdens,...

Multiplexed-tandem PCR for the specific diagnosis of gastrointestinal nematode infections in sheep: an European validation study

BackgroundTraditional methods of detecting and identifying gastrointestinal nematode infections in small ruminants, including sheep and goats, are time-consuming and lack in sensitivity and specificity. Recently, we developed an automated multiplexed-tandem (MT)-PCR platform for the diagnosis and identification patent infections with key genera/species of gastrointestinal nematodes of sheep and validated this approach in detailed experiments carried out in Australia. In the present study, we deployed this diagnostic platform in Scotland and Belgium to test samples from naturally infected sheep in these environments and to validate the MT-PCR platform relative to traditional diagnostic methods routinely used by local laboratories.ResultsMT-PCR detected all microscopy positive samples and there was a significant agreement between the results of the different test methods in terms of the species detected and their relative proportion in a test sample, however, for some samples, there were discrepancies between the results of the different test methods. Selective sequencing of purified MT-PCR products demonstrated the results to be 100% specific.ConclusionsThe MT-PCR platform is an advanced method for the species/genus-specific diagnosis of gastrointestinal nematode infections in small ruminants and has demonstrated utility when deployed in different countries and climatic zones. The platform is user-friendly due to the largely automated procedure and has high versatility in that it can achieve a specific diagnosis from different types of sample templates, including larval culture and faecal samples. With appropriate modifications of the primers used, the MT-PCR platform also provides potential for the diagnosis of a variety of other pathogens of veterinary or medical importance.

The host immune response to gastrointestinal nematode infection in sheep.

SummaryGastrointestinal nematode infection represents a major threat to the health, welfare and productivity of sheep populations worldwide. Infected lambs have a reduced ability to absorb nutrients from the gastrointestinal tract, resulting in morbidity and occasional mortality. The current chemo‐dominant approach to nematode control is considered unsustainable due to the increasing incidence of anthelmintic resistance. In addition, there is growing consumer demand for food products from animals not subjected to chemical treatment. Future mechanisms of nematode control must rely on alternative, sustainable strategies such as vaccination or selective breeding of resistant animals. Such strategies take advantage of the host's natural immune response to nematodes. The ability to resist gastrointestinal nematode infection is considered to be dependent on the development of a protective acquired immune response, although the precise immune mechanisms involved in initiating this process remain to be fully elucidated. In this study, current knowledge on the innate and acquired host immune response to gastrointestinal nematode infection in sheep and the development of immunity is reviewed.

An explicit immunogenetic model of gastrointestinal nematode infection in sheep.

Gastrointestinal nematodes are a global cause of disease and death in humans, wildlife and livestock. Livestock infection has historically been controlled with anthelmintic drugs, but the development of resistance means that alternative controls are needed. The most promising alternatives are vaccination, nutritional supplementation and selective breeding, all of which act by enhancing the immune response. Currently, control planning is hampered by reliance on the faecal egg count (FEC), which suffers from low accuracy and a nonlinear and indirect relationship with infection intensity and host immune responses. We address this gap by using extensive parasitological, immunological and genetic data on the sheep–Teladorsagia circumcincta interaction to create an immunologically explicit model of infection dynamics in a sheep flock that links host genetic variation with variation in the two key immune responses to predict the observed parasitological measures. Using our model, we show that the immune responses are highly heritable and by comparing selective breeding based on low FECs versus high plasma IgA responses, we show that the immune markers are a much improved measure of host resistance. In summary, we have created a model of host–parasite infections that explicitly captures the development of the adaptive immune response and show that by integrating genetic, immunological and parasitological understanding we can identify new immune-based markers for diagnosis and control.

Gastrointestinal nematode infections in sheep raised in Botucatu, state of São Paulo, Brazil.

Gastrointestinal nematode infections were evaluated in sheep raised in Botucatu, state of São Paulo, Brazil between April 2008 and March 2011. Every month, two tracer lambs grazing with a flock of sheep were exposed to natural infection with gastrointestinal nematodes for 28 consecutive days. At the end of this period, the lambs were sacrificed for worm counts. Haemonchus contortus presented 100% of prevalence. The seasons exerted no significant influence on the mean intensity of H. contortus, which ranged from 315 worms in November 2010 to 2,5205 worms in January 2011. The prevalence of Trichostrongylus colubriformis was also 100%, with the lowest mean intensity (15 worms) recorded in February 2011 and the highest (9,760 worms) in October 2009. In the case of T. colubriformis, a significant correlation coefficient was found between worm counts vs. rainfall (r = -0.32; P <0.05). Three other nematodes species were found in tracer lambs, albeit in small numbers. Their prevalence and mean intensity (in parenthesis) were as follows: Oesophagostomum columbianum 28% (25.2), Cooperia curticei 7% (4.5) and Trichuris spp. 2% (1). In conclusion, the environmental conditions of the area proved to be highly favorable for the year-round transmission of H. contortus and T. colubriformis.

A Review of the Epidemiology of Gastrointestinal Nematode Infections in Sheep and Goats in Ghana

In this paper, the gastrointestinal nematode parasites infecting small ruminants (sheep and goats) in Ghana and the epidemiological factors influencing their prevalence are reviewed and discussed. Twelve nematode species belonging to six families have been reported to infect these livestock in the country with Haemonchus contortus being the most prevalent helminth parasite in both animals. Parasitic gastroenteritis is caused by mixed infection of several nematode species. Management /husbandry practices, climate and host influence are found to be the main factors that affect gastrointestinal nematode infections in sheep and goats. Seasonal changes in the level of infective strongylate nematode larvae on pasture in the different agro-ecological zones of Ghana are reviewed. The number of infective larvae on pasture is reported to be directly related to the pattern of rainfall. Consequently, rainfall could be relied on to predict the rate of transmission of infection in grazing animals. Finally, the relevance of epidemiological knowledge in the development of efficient measures for controlling gastrointestinal nematode infections in sheep and goats in Ghana is discussed.

Integrated control of gastrointestinal nematodes in lambs using a bioactive feed × breed approach

Forages rich in condensed tannins have repeatedly shown potential to reduce gastrointestinal nematode infection in sheep. Similarly, several breeds of sheep have shown a relative resistance to gastrointestinal nematodes (GIN). We hypothesised that additive or even synergic effects may arise from the combination of a relatively resistant breed and a diet rich in condensed tannins. In study I, 160 lambs of the native Red Engadine Sheep (RES) and 113 lambs of the Swiss White Alpine sheep (SWA) were artificially infected with GIN and subsequently grazed for 52 days. The lambs were then distributed to 2 groups for a 14-day experimental feeding period. One group received a diet with a proportion of 55% sainfoin and was compared to a control group on the basis of faecal egg counts (FEC). In study II, 25 RES and 27 SWA lambs grazed infectious pastures for 37 days and were subsequently fed for 13 consecutive days with approximately 100% sainfoin or control forage. In addition to the FEC determination at the start and the end of the experimental feeding, the 52 lambs in study II were slaughtered and necropsied to determine their worm burden. FEC at the end of the feeding period were significantly lower in sainfoin fed lambs compared to controls in study I (p<0.001) as well as in study II (p=0.012). Breed, animal age, live weight, sex and the interaction of breed and treatment did not affect FEC in either study. The main nematode genera found in the sacrificed lambs of study II were Haemonchus spp., Teladorsagia spp., Nematodirus spp. and Trichostrongylus spp. Overall, RES had a significantly lower Haemonchus spp. (p=0.035) and Trichostrongylus spp. (p=0.003) worm burden compared to SWA. Regardless of breed, sainfoin feeding significantly reduced Teladorsagia spp. (p=0.049) and Nematodirus spp. (p<0.001) worm burden. Although, we could not demonstrate additive or synergic effects when using an integrated breed×sainfoin approach, the finding that a proportion of only 55% sainfoin in the diet led to a lower FEC compared to controls is important with respect to the implementation on producing farms.

Seasonal distribution of gastrointestinal nematode infections in sheep in a semiarid region, northeastern Brazil

The objective of this study was to determine the seasonal distribution and gastrointestinal nematode parasite load in crossbred Santa Inês tracer lambs, and to correlate the rainfall during the study period with occurrences of parasitic infections. Sixty-four male tracer lambs between the ages of four and eight months were used in the study. Two tracer lambs were inserted into the herd every 28 days to determine the pattern of infective larvae available in the environment. Variation in the fecal egg count (FEC) of nematodes was observed at the study site, with many samples containing undetectable parasite loads during the dry season. The larvae identified in coprocultures were Haemonchus sp., Trichostrongylus sp., Cooperia sp., Strongyloides sp. and Oesophagostomum sp. The nematodes recovered at necropsy were Haemonchus contortus, Trichostrongylus colubriformis, Cooperia punctata, C. pectinata, Trichuris sp., Oesophagostomum sp. and Skrajabinema ovis. The total number of larvae and the total number of immature and adult forms recovered from the tracers showed seasonal distributions that significantly correlated with the amount of rainfall received that month (p value ≅ 0.000 in all cases ). The species H. contortus was predominant in the herd and should be considered to be main pathogenic nematode species in these hosts under these conditions.

Comparative evaluation of two DNA isolation techniques for PCR-based diagnosis of gastrointestinal nematode infections in sheep

The specific diagnosis of gastrointestinal parasite infections in livestock is central to their control. PCR assays have been developed for routine diagnosis and to overcome limitations of classical methods. Central to the performance of such assays is the effective isolation of the nucleic acids from samples and the elimination of components that are inhibitory to PCR. Here, we directly compared two techniques for the isolation of DNA from strongylid nematode eggs from faecal samples from sheep, and assessed their performance in relation to the sensitivity and specificity of PCR, time required for DNA isolation and ease of use. The results showed differences in the performance of the two isolation techniques, subsequently effecting the PCR results. The main differences related to the time required for DNA isolation, and the elimination of inhibitory substances from the DNA isolated by one technique but not the other.

Establishment of a robotic, high-throughput platform for the specific diagnosis of gastrointestinal nematode infections in sheep

The accurate diagnosis of strongylid nematode infections is central to investigating their epidemiology and for parasite control. To overcome major limitations in sensitivity or specificity of traditional methods, including faecal egg count (FEC) and/or larval culture (LC), we evaluated and established a semi-automated, high throughput multiplexed-tandem PCR (MT-PCR) platform for the diagnosis of gastrointestinal strongylid nematode infections in sheep, and established its diagnostic sensitivity (100%) and specificity (87.5%) based on the testing of 100 faecal DNA samples from helminth-free sheep and 30 samples from sheep with infections confirmed by necropsy. Subsequently, the platform was employed to test 219 faecal samples from sheep with naturally acquired infections from various geographical localities within Australia and the results compared with those from conventional LC using 139 of the 219 samples. The results obtained using both MT-PCR and LC correlated significantly for most nematodes examined, but revealed that Oesophagostomum venulosum and Chabertia ovina (parasites of the large intestine) were significantly under-represented in the LC results. The results showed that Trichostrongylus spp. (87%), Teladorsagia circumcincta (80%) and Haemonchus contortus (67%) had the highest prevalences, followed by O. venulosum (51%) and C. ovina (12%). The molecular-diagnostic platform established can be used for species- or genus-specific diagnosis of patent nematode infections within 24h (compared with 7–10days for LC), and is a sensitive and cost effective tool for routine application in research and service laboratories.

The present status of anthelmintic resistance in gastrointestinal nematode infections of sheep in the northwest of Spain by in vivo and in vitro techniques

The aim of this study was to update the anthelmintic resistance (AR) status in sheep flocks infected by gastrointestinal nematodes (GIN) by means of in vivo and in vitro methods in the northwest of Spain. With this objective, we studied the efficacy of benzimidazoles (BZs), imidazothiazoles (IMs) and macrocyclic lactones (MLs), between 2006 and 2011. The sampling area was the Autonomous Community of Castilla y León but the majority of the flocks were located in the province of León. When the mean of GIN eggs per gram (epg) in faeces in a flock was higher than 150, the in vivo Faecal Egg Count Reduction Test (FECRT) was carried out. According to this test, AR was present in 63.6% of flocks, independently of the anthelmintic used. Flocks were mainly resistant to levamisole (LEV) (59.0%), followed by ivermectin (IVM) (27.3%) and albendazole (13.6%). Multidrug-resistance was also observed in 27.2% of the flocks, one of them being resistant to all anthelmintic families, including long-acting moxidectin. Comparing the evolution of AR in the last decade, between 1999 and 2011, the level of resistance to BZs and MLs was fairly constant throughout the time by means of the FECRT. However, the resistance to LEV increased significantly in only one decade since during the period 1999–2003 the percentage was 38.5%. The AR status was also measured by in vitro techniques in those flocks with an egg output lower than 150 epg. The prevalence of AR to BZs reached the 35.3% by Egg Hatch Assay. However, the level of resistance reported for LEV and IVM was 61.5% and 23.5%, respectively, by using the Larval Feeding Inhibition Assay, percentages very similar to those reported with the FECRT.

The effects of climate change on ovine parasitic gastroenteritis determined using veterinary surveillance and meteorological data for Northern Ireland over the period 1999–2009

While the influence of temperature and moisture on the free-living stages of gastrointestinal nematodes have been described in detail, and evidence for global climate change is mounting, there have been only a few attempts to relate altered incidence or seasonal patterns of disease to climate change. Studies of this type have been completed for England Scotland and Wales, but not for Northern Ireland (NI). Here we present an analysis of veterinary diagnostic data that relates three categories of gastrointestinal nematode infection in sheep to historical meteorological data for NI. The infections are: trichostrongylosis/teladorsagiosis (Teladorsagia/Trichostrongylus), strongyloidosis and nematodirosis. This study aims to provide a baseline for future climate change analyses and to provide basic information for the development of nematode control programmes. After identifying and evaluating possible sources of bias, climate change was found to be the most likely explanation for the observed patterns of change in parasite epidemiology, although other hypotheses could not be refuted. Seasonal rates of diagnosis showed a uniform year-round distribution for Teladorsagia and Trichostrongylus infections, suggesting consistent levels of larval survival throughout the year and extension of the traditionally expected seasonal transmission windows. Nematodirosis showed a higher level of autumn than Spring infection, suggesting that suitable conditions for egg and larval development occurred after the Spring infection period. Differences between regions within the Province were shown for strongyloidosis, with peaks of infection falling in the period September–November. For all three-infection categories (trichostrongylosis/teladorsagiosis, strongyloidosis and nematodirosis), significant differences in the rates of diagnosis, and in the seasonality of disease, were identified between regions.

Climate and the epidemiology of gastrointestinal nematode infections of sheep in Europe

The free-living stages of gastrointestinal nematode parasites of sheep are strongly affected by climate. Thus, extreme heat and cold are detrimental to development and survival, while, within tolerable limits, increasing temperatures generally accelerate development but increase mortality. Moisture is needed for development and translation of larvae from faeces to pasture, and so rainfall is a limiting factor for transmission. Together, these factors underpin seasonal patterns of infection in sheep, as well as geographic variation in the epidemiology and relative importance of different species within Europe. Local knowledge and experience enable treatment to be targeted appropriately to prevent dangerous levels of infection. This traditional know-how can be supplemented by predictive epidemiological models, built on thorough understanding of the influence of climate on larval availability. However, management also has a dominant role in determining patterns of infection, and is itself influenced by climate. Current geographic variation in nematode epidemiology across Europe, and knowledge of systems from outside Europe, can provide only limited perspectives on the likely effects of climate change on disease in future. This is because disease arises from complex interaction between host and parasite factors, and the implementation of optimal control strategies to meet new challenges will be slowed by the inertia of current systems. Approaches to nematode control must therefore take account not only of parasite biology, but also the forces that shape sheep farming systems and management decisions.

Pharmaceutical treatments of gastrointestinal nematode infections of sheep—Future of anthelmintic drugs

Various interacting factors have been identified to explain why health plans for nematode parasite control, based on conventional epidemiological knowledge and involving pharmaceutical treatments of their sheep hosts have become unsustainable. Of these, the emergence of anthelmintic resistance has had a major impact on the economics of sheep farming, necessitating fundamental managemental changes. This review focusses on the use of anthelmintic drugs for the control of gastrointestinal nematode infections in sheep, emphasising the need to develop sustainable strategies in the face of inevitable parasite evolution in response to exposure to anthelmintic drugs and other noxious stimuli, or favourable opportunities resulting from changing animal management and climatic factors.