Abomasal nematode species differ in their in vitro response to exsheathment triggers.

A crucial step in the infection process of grazing ruminants by gastro-intestinal nematodes is the exsheathment of the infective third-stage larva following ingestion. Recently, heat shock was shown to play an important role in the carbon dioxide (CO2)-dependent exsheathment response in Haemonchus contortus. The current in vitro study set out to evaluate the role of heat shock in other abomasal species. In rumen fluid, all species tested exsheathed rapidly and efficiently in response to heat shock and CO2. This response was significantly higher compared to slow temperature changes, supporting the hypothesis that heat shock plays an important role in vivo. However, in artificial buffer, the effect of heat shock was species-dependent. For H. contortus and Ostertagia leptospicularis, the response in artificial buffer was similar to rumen fluid. In contrast, Ostertagia ostertagi and Teladorsagia circumcincta exsheathment was significantly lower and/or slower in artificial buffer, and there was no benefit of heat shock. For these two species, it appears that there are co-factors in the rumen fluid, in addition to heat shock and CO2, contributing to exsheathment. Overall, the data indicate that there are significant differences between abomasal species in their response to exsheathment triggers.

Exploring the mechanisms of resistance to Teladorsagia circumcincta infection in sheep through transcriptome analysis of abomasal mucosa and abomasal lymph nodes.

The present study exploited the RNA-seq technology to analyze the transcriptome of target tissues affected by the Teladorsagia circumcincta infection in two groups of adult ewes showing different statuses against gastrointestinal nematode (GIN) infection with the aim of identifying genes linked to GIN infection resistance in sheep. For this, based on the accumulated faecal egg count of 18 adult Churra ewes subjected to a first experimental infection with T. circumcincta, six ewes were classified as resistant and six others as susceptible to the infection. These 12 animals were dewormed and infected again. After humanitarian sacrifice of these 12 animals at day 7 post-infection, RNA samples were obtained from abomasal mucosa and lymph node tissues and RNA-Seq datasets were generated using an Illumina HiSeq 2000 sequencer. The distribution of the genes based on their expression level were very similar among the two different tissues and conditions. The differential expression analysis performed with two software (DESeq and EdgeR) only identified common differentially expressed genes (DEGs), a total of 106, in the lymph node samples which were considered as GIN-activated. The enrichment analysis performed for these GIN-activated genes identified some pathways related to cytokine-mediated immune response and the PPARG signaling pathway as well as disease terms related to inflammation and gastro-intestinal diseases as enriched. A systematic comparison with the results of previous studies confirmed the involvement of genes such as ITLN2, CLAC1 and galectins, in the immune mechanism activated against T. circumcincta in resistant sheep.

Characterization of Ostertagia ostertagi annexin-like proteins at different developmental stages.

Ostertagiosis remains an economically important parasitic disease in cattle in the temperate regions of the world. Repeated exposures to Ostertagia ostertagi in calves cause significant pathology in the abomasum but elicit little protective immunity. The larvae use the host's gastric glands as a niche for development, where the parasite completes its parasitic stages, while in the gastric glands, the larvae must down-regulate the host inflammatory immune responses. Annexin (ANX) A1, commonly found in most eukaryotes, is heavily involved in controlling anti-inflammatory responses by binding receptors on leukocytes. We hypothesized, therefore, that parasite proteins of the ANX family may be involved in host-parasite interactions during ostertagiosis. BLASTN search with the bovine ANXA1 identified two families of Oos-ANX like proteins (Oos-ANXL), each of which was highly conserved at the genetic level and identical at the amino acid sequence level. Oos-ANXL-1 is encoded by two transcripts and Oos-ANXL-2 by 20 transcripts. The present study characterized one Oos-ANXL, representing the most abundant Oos-ANXL, which was further defined as Oost-ANXL-2.1. Oos-ANXL-2.1 with a coding sequence of 519 bp was PCR-amplified, cloned, and expressed. Oos-ANXL-2.1 was immunolocalized to both L3 and adult, but not L4. The staining appeared to be associated with the gut and hypodermis in L3, but it was specifically localized to the hypodermis in adult worms. Western blots detected three protein bands in parasite lysates using anti-recombinant Oos-ANXL-2.1 antibody. Integrated optical density for each of the 3 Oos-ANXL-2s or the total Oos-ANXL-2s detected by Western blots (P < 0.05) was higher in adult worms than in L3 or L4. The results indicate that the production of Oos-ANXL-2s is developmentally regulated and most abundant in the adult worm. This rather large family of proteins could be a potential vaccine target against O. ostertagi infection and warrants further investigation.

Anthelmintic effects of forage chicory (Cichorium intybus) against gastrointestinal nematode parasites in experimentally infected cattle.

Two experiments studied the effects of dietary chicory against gastrointestinal nematodes in cattle. In Experiment (Exp.) 1, stabled calves were fed chicory silage (CHI1; n = 9) or ryegrass/clover hay (CTL1; n = 6) with balanced protein/energy intakes between groups. After 16 days, all calves received 10 000 Ostertagia ostertagi and 66 000 Cooperia oncophora third-stage larvae (L3) [day (D) 0 post-infection (p.i.)]. In Exp. 2, calves were assigned to pure chicory (CHI2; n=10) or ryegrass/clover (CTL2; n = 10) pastures. After 7 days, animals received 20 000 O. ostertagi L3/calf (D0 p.i.) and were moved regularly preventing pasture-borne infections. Due to poor regrowth of the chicory pasture, CHI2 was supplemented with chicory silage. At D40 p.i. (Exp. 1) and D35 p.i. (Exp. 2) calves were slaughtered for worm recovery. In Exp.1, fecal egg counts (FEC) were similar between groups. However, O. ostertagi counts were significantly reduced in CHI1 by 60% (geometric mean; P < 0·01), whereas C. oncophora burdens were unaffected (P = 0·12). In Exp. 2, FEC were markedly lowered in CHI2 from D22 p.i onwards (P < 0·01). Ostertagia ostertagi adult burdens were significantly reduced in CHI2 by 66% (P < 0·001). Sesquiterpene lactones were identified only in chicory (fresh/silage). Chicory shows promise as an anti-Ostertagia feed for cattle and further studies should investigate its on-farm use.

Desiccation tolerance of gastrointestinal nematode third-stage larvae: exploring the effects on survival and fitness.

The free-living third-stage larvae (L3) of gastrointestinal nematodes are able to tolerate extreme weather conditions such as desiccation, but little is known about the consequent effects this has on their fitness. This study explored how the desiccation of Haemonchus contortus L3 larvae affected their absolute fitness by examining their success at consequent life cycle stages for a complete generation, and comparing them against a control. The stages examined include establishment, fecundity, larval development and pathogenicity. The results show that while desiccation greatly reduced the survival of the L3 prior to infection in sheep, their absolute fitness was not negatively impacted. Instead, it appears desiccation slightly augmented H. contortus fitness by triggering increases in fecundity. The study further explored what influence different gastrointestinal nematode (GIN) species (H. contortus, Trichostrongylus colubriformis, Teladorsagia circumcincta), isolates and age of L3 had on their capacity to revive following various periods of desiccation. The results showed desiccation tolerance varied as a function of each of these variables. The greatest L3 survival was found in Te. circumcincta followed by Tr. colubriformis and finally H. contortus. Significant variation was observed between individual species isolates and as a function of age. The results of this study carry important practical implications for the epidemiological understanding of gastrointestinal nematode species of economic importance.

The reindeer abomasal nematode (Ostertagia gruehneri) is naturally transmitted to sheep when sharing pastures.

The increasing number of sheep (Ovis aries) in northern Finland, often alternately corralled with winter-fed reindeer (Rangifer tarandus tarandus), creates potential for cross-infection of gastrointestinal nematodes. The aim of this study was to elucidate this possibility with 43 animals. Eleven reindeer and 8 sheep had shared a corral by turns, reindeer during winters, and sheep in summers. Another 12 reindeer had no known contact with sheep. Twelve sheep had no close contact to other ruminants. Both reindeer groups were free-ranging during summers. During slaughter in September to November, 2003, abomasa and parts of intestines were collected. Gastrointestinal nematodes were counted and identified. The species found were the following: in reindeer, Ostertagia gruehneri/Ostertagia arctica, Mazamastrongylus dagestanica, Nematodirus tarandi, Nematodirella longissimespiculata and Bunostomum trigonocephalum; in sheep, Teladorsagia circumcincta/Teladorsagia trifurcata, O. gruehneri/O. arctica, Nematodirus filicollis and N. spathiger. In the sheep sharing corral with reindeer, the only abomasal nematode species found was O. gruehneri, a reindeer parasite. The generation interval of O. gruehneri in Finnish reindeer appears to be shorter than in Canadian Arctic caribou, where complete larval inhibition leading to only one generation yearly has been reported.

Analysis of cell hyperplasia and parietal cell dysfunction induced by Ostertagia ostertagi infection.

Infections in cattle with the gastric nematode Ostertagia ostertagi are associated with decreased acid secretion and profound physio-morphological changes of the gastric mucosa. The purpose of the current study was to investigate the mechanisms triggering these pathophysiological changes. O. ostertagi infection resulted in a marked cellular hyperplasia, which can be explained by increased transcriptional levels of signaling molecules related to the homeostasis of gastric epithelial cells such as HES1, WNT5A, FGF10, HB-EGF, AREG, ADAM10 and ADAM17. Intriguingly, histological analysis indicated that the rapid rise in the gastric pH, observed following the emergence of adult worms, cannot be explained by a loss of parietal cells, as a decrease in the number of parietal cells was only observed following a long term infection of several weeks, but is likely to be caused by an inhibition of parietal cell activity. To investigate whether this inhibition is caused by a direct effect of the parasites, parietal cells were co-cultured with parasite Excretory/Secretory products (ESP) and subsequently analyzed for acid production. The results indicate that adult ESP inhibited acid secretion, whereas ESP from the L4 larval stages did not alter parietal cell function. In addition, our data show that the inhibition of parietal cell activity could be mediated by a marked upregulation of inflammatory factors, which are partly induced by adult ESP in abomasal epithelial cells. In conclusion, this study shows that the emergence of adult O. ostertagi worms is associated with marked cellular changes that can be partly triggered by the worm's Excretory/secretory antigens.

Exploring the abomasal lymph node transcriptome for genes associated with resistance to the sheep nematode Teladorsagia circumcincta.

This study exploited Blackface lambs that varied in their resistance to the abomasal nematode parasite, Teladorsagia circumcincta. Infection of these lambs over 3 months identified susceptible (high adult worm count, high faecal egg count and low IgA antibody) and resistant animals that had excluded all parasites. Previous work had shown that susceptibility and resistance is dependent on the differential immune response to the parasite, which occurs within the abomasal (gastric) lymph node (ALN) that drains the site of infection. The Affymetrix ovine gene array was used to interrogate the transcriptome of the ALN to identify genes and physiological pathways associated with resistance. We used a bovine RT-qPCR array of 84 genes to validate the gene array, and also report digital gene expression analysis on the same tissues, reanalysed using the Oar v3.1 sheep genome assembly. These analyses identified Humoral Immune Response, Protein Synthesis, Inflammatory Response and Hematological System Development and Function as the two top-ranked networks associated with resistance. Central genes within these networks were IL4, IL5, IL13RA2 and in particular IL13, which confirmed that differential activation of Th2 polarized responses is critical to the resistance phenotype. Furthermore, in resistant sheep there was up-regulation of genes linked to control and suppression of inflammation. The identity of differentially-expressed chemokines and receptors in the resistant and susceptible sheep also begins to explain the cellular nature of the host response to infection. This work will greatly help in the identification of candidate genes as potential selectable markers of genetic resistance.

Relationship between susceptibility of Blackface sheep to Teladorsagia circumcincta infection and an inflammatory mucosal T cell response.

Teladorsagia circumcincta is the most economically important gastrointestinal (abomasal) nematode parasite of sheep in cool temperate regions, to which sheep show genetically-varying resistance to infection. Lambs, from parents with genetic variation for resistance, were trickle infected with L3 larvae over 12 weeks. 45 lambs were identified with a range of susceptibilities as assessed by: adult worm count at post mortem, faecal egg count (FEC) and IgA antibody levels. This project investigated the correlation of T cell cytokine expression and resistance to infection at the mature stage of response, when the resistant lambs had excluded all parasites.Histopathology showed only minor changes in resistant animals with a low level lymphocyte infiltration; but in susceptible lambs, major pathological changes were associated with extensive infiltration of lymphocytes, eosinophils and neutrophils.Absolute quantitative RT-qPCR assays on the abomasal lymph node (ALN) revealed a significant positive correlation between IL6, IL21 and IL23A transcript levels with adult worm count and FEC. IL23A was also negatively correlated with IgA antibody levels. Significantly positive correlation of TGFB1 levels with adult worm count and FEC were also seen in the abomasal mucosa. These data are consistent with the hypothesis that the inability to control L3 larval colonization, adult worm infection and egg production is due to the activation of the inflammatory Th17 T cell subset.

Obligate larval inhibition of Ostertagia gruehneri in Rangifer tarandus? Causes and consequences in an Arctic system.

Larval inhibition is a common strategy of Trichostrongylidae nematodes that may increase survival of larvae during unfavourable periods and concentrate egg production when conditions are favourable for development and transmission. We investigated the propensity for larval inhibition in a population of Ostertagia gruehneri, the most common gastrointestinal Trichostrongylidae nematode of Rangifer tarandus. Initial experimental infections of 4 reindeer with O. gruehneri sourced from the Bathurst caribou herd in Arctic Canada suggested that the propensity for larval inhibition was 100%. In the summer of 2009 we infected 12 additional reindeer with the F1 and F2 generations of O. gruehneri sourced from the previously infected reindeer to further investigate the propensity of larval inhibition. The reindeer were divided into 2 groups and half were infected before the summer solstice (17 June) and half were infected after the solstice (16 July). Reindeer did not shed eggs until March 2010, i.e. 8 and 9 months post-infection. These results suggest obligate larval inhibition for at least 1 population of O. gruehneri, a phenomenon that has not been conclusively shown for any other trichostrongylid species. Obligate inhibition is likely to be an adaptation to both the Arctic environment and to a migratory host and may influence the ability of O. gruehneri to adapt to climate change.

Development and availability of the free-living stages of Ostertagia gruehneri, an abomasal parasite of barrenground caribou (Rangifer tarandus groenlandicus), on the Canadian tundra.

Climate change in the Arctic is anticipated to alter the ecology of northern ecosystems, including the transmission dynamics of many parasite species. One parasite of concern is Ostertagia gruehneri, an abomasal nematode of Rangifer ssp. that causes reduced food intake, weight loss, and decreased pregnancy rates in reindeer. We investigated the development, availability, and overwinter survival of the free-living stages of O. gruehneri on the tundra. Fecal plots containing O. gruehneri eggs were established in the Northwest Territories, Canada under natural and artificially warmed conditions and sampled throughout the growing season of 2008 and the spring of 2009. Infective L3 were present 3-4 weeks post-establishment from all trials under both treatments, except for the trial established 4 July 2008 under warmed conditions wherein the first L3 was recovered 7 weeks post-establishment. These plots were exposed to significantly more time above 30°C than the natural plots established on the same date, suggesting a maximum temperature threshold for development. There was high overwinter survival of L2 and L3 across treatments and overwintering L2 appeared to develop to L3 the following spring. The impact of climate change on O. gruehneri is expected to be dynamic throughout the year with extreme maximum temperatures negatively impacting development rates.

Infection with the gastrointestinal nematode Ostertagia ostertagi in cattle affects mucus biosynthesis in the abomasum.

The mucus layer in the gastrointestinal (GI) tract is considered to be the first line of defense to the external environment. Alteration in mucus components has been reported to occur during intestinal nematode infection in ruminants, but the role of mucus in response to abomasal parasites remains largely unclear. The aim of the current study was to analyze the effects of an Ostertagia ostertagi infection on the abomasal mucus biosynthesis in cattle. Increased gene expression of MUC1, MUC6 and MUC20 was observed, while MUC5AC did not change during infection. Qualitative changes of mucins, related to sugar composition, were also observed. AB-PAS and HID-AB stainings highlighted a decrease in neutral and an increase in acidic mucins, throughout the infection. Several genes involved in mucin core structure synthesis, branching and oligomerization, such as GCNT3, GCNT4, A4GNT and protein disulphide isomerases were found to be upregulated. Increase in mucin fucosylation was observed using the lectin UEA-I and through the evaluation of fucosyltransferases gene expression levels. Finally, transcription levels of 2 trefoil factors, TFF1 and TFF3, which are co-expressed with mucins in the GI tract, were also found to be significantly upregulated in infected animals. Although the alterations in mucus biosynthesis started early during infection, the biggest effects were found when adult worms were present on the surface of the abomasal mucosa and are likely caused by the alterations in mucosal cell populations, characterized by hyperplasia of mucus secreting cells.

A differential interplay between the expression of Th1/Th2/Treg related cytokine genes in Teladorsagia circumcincta infected DRB1*1101 carrier lambs.

Substantial debate exists on whether the immune response between sheep resistant and susceptible to gastrointestinal nematodes can be differentiated into a Th1 and Th2 phenotype. The present study addresses the hypothesis that variation in resistance to Teladorsagia circumcincta between DRB1*1101 (associated with reduced faecal egg count and worm burden) carriers and non-carriers is due to a differential interplay in the expression of Th1/Th2 and regulatory T (Treg) related cytokine genes. Lambs from each genotype were either slaughtered at day 0 (un-infected control) or infected with 3 × 10(4) Teladorsagia circumcincta L3 and slaughtered at 3, 7, 21, and 35 days later. Lambs carrying the DRB1*1101 allele had a significantly lower worm burden (P < 0.05) compared to the non-carriers. Abomasal mucosal cytokine gene expression was evaluated by quantitative real-time PCR and comparison made for time and genotype effects. The response generated varied through the course of infection and was affected by genotype. DRB1*1101 carriers had an up-regulated expression of the Th1-related cytokine genes (IL-1ß, TNFα, and IFN-γ) at day 3, but this was replaced by an up-regulated expression of Th2-related cytokine genes (IL-10 and IL-13) and Treg-related cytokine genes (IL-2RA-CD25, TGFα, TGFß, Arg2, MIF and FOXP3) by day 7. Conversely, in the non-carriers these changes in gene expression were delayed until days 7 and 21 post infection (pi), respectively. It is concluded that resistance to Teladorsagia circumcincta in animals carrying the DRB1*1101 allele is influenced by an earlier interplay between Th1, Th2 and T regulatory immune response genes.

The dynamic influence of the DRB1*1101 allele on the resistance of sheep to experimental Teladorsagia circumcincta infection.

Suffolk sheep carrying the DRB1*1101 (previously referred to as-DRB1*0203 or G2) allele have been reported to show increased resistance to natural Teladorsagia circumcincta infection compared to non-carriers. The objective of this study was to compare the biochemical and physiological responses of DRB1*1101 carrier and non-carrier twin lambs to an experimental infection with 3 × 10(4) L3 Teladorsagia circumcincta. The variables studied included worm burden, faecal egg count, abomasal mast cells, IgA, IgE, IgG1 plus IgG2 and haematological parameters at 0, 3, 7, 21 and 35 days post infection (dpi), and duodenal smooth muscle contractility at 0 and 35 dpi. DRB1*1101 carrier lambs had significantly lower worm burden, higher mast cell and plasma platelet counts than the DRB1*1101 non-carriers (P < 0.05). Before infection, the non-carrier lambs exhibited significantly higher mucosal levels of all antibody isotypes measured compared to the carriers; these levels remained relatively stable over the course of infection in the non-carriers while there was a slow build up of these antibodies in the carriers up to day 21 post infection (pi). The DRB1*1101 non-carrier lambs had a significantly higher plasma lymphocyte count, and produced greater duodenal contractile force relative to the carrier lambs (P < 0.05). There was no significant difference between genotypes in the level of plasma eosinophils, monocytes, neutrophils or FEC. This evidence suggests that resistance conferred by DRB1*1101 is acquired rather than innate, depends on worm expulsion rather than fecundity and is dependent on mucosal mast cell proliferation, platelet activation, and IgA and IgE antibody responses.

The efficacy of an ivermectin/closantel injection against experimentally induced infections and field infections with gastrointestinal nematodes and liver fluke in cattle.

Three studies were performed to test the efficacy of an ivermectin/closantel injection (200 microg/kg(-1) ivermectin and 5 mg/kg(-1) closantel) in cattle. Two were experimentally induced infections of Ostertagia ostertagi, Cooperia oncophora and Fasciola hepatica in calves, and the third had natural field infections in cattle with several species of gastrointestinal nematodes and F. hepatica. In the two studies with artificial infections, four groups of 8 calves were used. All calves were infected with metacercariae on Day 0. Infection with the nematodes took place on Day 33 in groups 1 and 2 and on Day 54 in groups 3 and 4. Treatment was given to calves of group 1 on Day 63 and to calves of group 3 on Day 84. Calves of groups 2 and 4 served as untreated control groups. Calves of groups 1 and 2 were sacrificed on Day 84, calves of groups 3 and 4 on Day 105. The field study was carried out on a commercial farm in the Netherlands. Six groups of cattle were used. Groups A and B consisted of 10 parasite free calves, introduced to the farm and grazed for four weeks on pastures naturally infected with gastrointestinal nematode larvae and liver fluke metacercariae. Group C were the farmers own calves (15), group D heifers (10), group E dry cows (6) and group F milking cows (20). Treatment was given to animals of group A, C, D and E 10 weeks after housing of group A and B. Animals of groups B and F served as untreated controls. Calves of groups A and B were sacrificed 14 days after treatment. The efficacy of the treatment was calculated on basis of the post-mortem fluke and nematode worm counts in the first two studies and on a combination of post-mortem fluke and nematode worm counts and faecal egg output in the field study. In the two experimental studies, the efficacy of the treatment against F. hepatica was 99.2% and 94.5% for 9-week-old flukes and 98.4% and 99.5% for 12-week-old flukes. For O. ostertagi in both studies efficacy was 100% and against C. oncophora in both Groups 1 efficacy was 84.9% and 99.0% and in Groups 3 85.0% and 99.4%. In the field study, based on the post mortem fluke and nematode worm counts in groups A and B, efficacy against F. hepatica was 98.4%, O. ostertagi 100%, C. oncophora 99.4%, C. punctata 100%, Nematodirus helvetianus 60.8%, Trichuris spp. 100% and against larval intestinal nematodes 100%. The results of the faecal examinations 14 days after treatment confirmed the post-mortem results with 100% reduction of egg output for O. ostertagi, C. punctata, Trichostrongylus spp. and Trichuris spp. and low egg output of C. oncophora and N. helvetianus.

Host specificity and species diversity of the Ostertagiinae Lopez-Neyra, 1947 in ruminants: a European perspective.

BACKGROUND: Nematodes of the subfamily Ostertagiinae appear to be rather specific to a species or family of hosts, but some are observed in a wide variety of hosts. The nematode Ostertagia leptospicularis draws special attention due to its presence or absence among the same host species in different European countries. Therefore, this paper focuses mainly on the host specificity among nematodes of the subfamily Ostertagiinae. The second aim of this study is to assess the possibility of treating O. leptospicularis as an Ostertagia species complex. METHODS: Data were gathered from post-mortem examinations of domestic and wild ruminants (n = 157), as well as bibliographical references (n = 96), which were pooled and discussed. The research area was limited to European countries, hence the studied ostertagiine species are limited to native ones; likewise, the host species. Special emphasis was placed on the mean abundance values that allowed a typical host or hosts for each nematode species to be specified. Correspondence analysis was performed to confirm the stated host specificity. RESULTS: The analysis revealed that nematodes of this subfamily tend to use ruminants from a particular subfamily as their principal host. The results indicate that Ostertagia leptospicularis, similar to Teladorsagia circumcincta, may represent a potential species complex. This nematode, as the sole member of the subfamily Ostertagiinae, occurs in almost all representatives of the Bovidae subfamily, as well as in the Cervidae. CONCLUSIONS: Despite the stated narrow host specificity, the results obtained may suggest that O. leptospicularis is not strongly connected to any host or is comparably associated with a very wide and diverse group of hosts (Cervidae, Bovidae). The Ostertagia complex may have particular cryptic species or strains typical for any individual host or group of hosts. Such a conclusion requires further investigations on a wider scale.

Apparent prevalence of and risk factors for infection with Ostertagia ostertagi, Fasciola hepatica and Dictyocaulus viviparus in Swiss dairy herds.

Infections with helminth parasites can negatively affect performance of dairy cows. Knowledge on infection intensity, spatial distributions and risk factors are key to develop targeted treatment strategies. Canada and most EU countries have conducted large investigations, but respective data for Switzerland were missing. We now performed a bulk tank milk serosurvey for Ostertagia ostertagi, Fasciola hepatica, and Dictyocaulus viviparus on a total of 1036 voluntarily participating dairy herds that were sampled at confinement periods, i.e. in winter 2014/15 or 2015/16, respectively. All samples were analyzed with commercial ELISAs for antibodies (AB) against O. ostertagi and F. hepatica, and those of the first sampling period additionally with an in-house ELISA for AB against D. viviparus. Testing for the latter parasite was not done in the second year of the study, as the sampling period might have missed infections due to the short lived nature of specific antibodies. The possible influence of geographic, climatic, and farm management variables on AB levels were assessed for each parasite using scanning cluster and multiple regression analysis. Overall seroprevalence for O. ostertagi was 95.5% (95% C.I.: 94.0-96.6), with a mean optical density ratio (ODR) of 0.83, for F. hepatica 41.3% (95% C.I.: 38.3-44.4), and for D. viviparus 2.9% (95% C.I.: 1.6-4.7). There were no significant differences between the two sampling periods. For all parasites, significant geographic clusters of higher AB levels could be established. Furthermore, AB levels against all three parasites were positively correlated with each other, indicating either cross-reactions or co-infections. For O. ostertagi, herd size and percentage of pasture in the ration were positively correlated with AB levels. For F. hepatica, altitude above sea level (a.s.l.) positively, and milk production per cow and year was negatively correlated with AB levels. This work provides baseline data for further studies performing in-depth risk factor analysis and investigating management as well as targeted treatment options to control the parasites.

Thermotolerance of L3 Ostertagia (Teladorsagia) circumcincta and some of its enzymes.

Parasitic nematodes of ruminants can be expected to experience temperatures in excess of 40 degrees C in faeces on pasture and, perhaps, in the host. L3 Ostertagia (Teladorsagia) circumcincta survived for at least 90 min at 45 degrees C in vitro in water, but the larvae were inactivated rapidly by only slightly higher temperatures. The glycolytic enzymes hexokinase and pyruvate kinase were inactivated in a similar temperature range, whereas malate dehydrogenase maintained its activity at temperatures in excess of 50 degrees C. These data imply that the loss of glycolytic activity might explain the loss of larval motility at temperatures between 45 degrees C and 50 degrees C.

Economic modelling of grazing management against gastrointestinal nematodes in dairy cattle.

Grazing management (GM) interventions, such as reducing the grazing time or mowing pasture before grazing, have been proposed to limit the exposure to gastrointestinal (GI) nematode infections in grazed livestock. However, the farm-level economic effects of these interventions have not yet been assessed. In this paper, the economic effects of three GM interventions in adult dairy cattle were modelled for a set of Flemish farms: later turnout on pasture (GM1), earlier housing near the end of the grazing season (GM2), and reducing the daily grazing time (GM3). Farm accountancy data were linked to Ostertagia ostertagi bulk tank milk ELISA results and GM data for 137 farms. The economic effects of the GM interventions were investigated through a combination of efficiency analysis and a whole-farm simulation model. Modelling of GM1, GM2 and GM3 resulted in a marginal economic effect of € 8.36, € -9.05 and € -53.37 per cow per year, respectively. The results suggest that the dairy farms can improve their economic performance by postponing the turnout date, but that advancing the housing date or reducing daily grazing time mostly leads to a lower net economic farm performance. Overall, the GM interventions resulted in a higher technical efficiency and milk production but these benefits were offset by increased feed costs as a result of higher maintenance and cultivation costs. Because the results differed highly between farms, GM interventions need to be evaluated at the individual level for appropriate decision support.

Mathematical models to assess strategies for the control of gastrointestinal roundworms in cattle 1. Construction.

Mathematical models were constructed to simulate the effect of Ostertagia ostertagi infections on the growth of young cattle. The equations are based on System Dynamics using the DYSMAP 2 software package in their construction. A pasture and animal growth model simulates the growth of pasture and the influences of management and climate on it; cattle feed intake and conversion into energy for maintenance and liveweight gain; the effect of the parasite burden on feed intake and utilization of energy. This model was then combined with one of the life cycle of O. ostertagi in order to determine the effect of worm burdens on animal growth rate in a range of farm conditions, such as stocking rate, grazing history of the pasture, and rainfall. By converting the resultant liveweight gain into a monetary value, an economic assessment of alternative worm control strategies can be made. In this paper the construction of the models with equations and assumptions is given in detail.