Characterisation of protective vaccine antigens from the thiol-containing components of excretory/secretory material of Ostertagia ostertagi.

Previous vaccination trials have demonstrated that thiol proteins affinity purified from Ostertagia ostertagi excretory-secretory products (O. ostertagi ES-thiol) are protective against homologous challenge. Here we have shown that protection induced by this vaccine was consistent across four independent vaccine-challenge experiments. Protection is associated with reduced cumulative faecal egg counts across the duration of the trials, relative to control animals. To better understand the diversity of antigens in O. ostertagi ES-thiol we used high-resolution shotgun proteomics to identify 490 unique proteins in the vaccine preparation. The most numerous ES-thiol proteins, with 91 proteins identified, belong to the sperm-coating protein/Tpx/antigen 5/pathogenesis-related protein 1 (SCP/TAPS) family. This family includes previously identified O. ostertagi vaccine antigens O. ostertagi ASP-1 and ASP-2. The ES-thiol fraction also has numerous proteinases, representing three distinct classes, including: metallo-; aspartyl- and cysteine proteinases. In terms of number of family members, the M12 astacin-like metalloproteinases, with 33 proteins, are the most abundant proteinase family in O. ostertagi ES-thiol. The O. ostertagi ES-thiol proteome provides a comprehensive database of proteins present in this vaccine preparation and will guide future vaccine antigen discovery projects.

Repeated, drug-truncated infections with Ostertagia ostertagi elicit strong humoral and cell-mediated immune responses and confer partial protection in cattle.

Bovine ostertagiasis causes significant production losses to the cattle industry. Protective immunity induced by natural infection is slow to develop and anthelmintic resistance is rapidly developing. There is a need to advance alternatives for control of gastrointestinal nematode parasites. The present study investigated the effects of repeated, drug-truncated infections (rDTI) on development of protective immunity and attenuation of a challenge infection by O. ostertagi. Helminth-free calves were randomly assigned to either a rDTI or a control group (n = 5). The rDTI group received daily oral infections of 5000 Ostertagia L3 for 5 consecutive days, then were drug-treated on 14 and 15 days post infection (dpi), to attenuate O. ostertagi at the late fourth larval (L4) through young adult stages. DTI was repeated 3 weeks after the drug treatment. A total of 5 DTIs were administered to the DTI-treated animals. Non-DTI-treated, control animals received tap water as infection control. All animals were drug-treated at the same time. Animals were challenge-infected 4 weeks following the final round of rDTI. The results show that eggs per gram of feces (EPG) in the rDTI group were significantly reduced (P < 0.05) from 21 to 39 dpi, with an overall reduction in cumulative EPG. The control group exhibited reduced (P = 0.0564) average weight gains when compared to those of the rDTI group during weeks 4-5 post infection, a period coinciding with peak EPG output of control animals. Antigen-specific IgG, IgE and IgA responses were detected after the 2nd DTI, and stronger antibody recall responses were elicited by challenge infection. High levels of antigen-specific peripheral blood mononuclear cell (PBMC)/T cell proliferation to whole worm and excretory-secretory (ES) antigens were detected in rDTI-treated animals. These data indicate that partial protective immunity against ostertagiasis, involving cell-mediated and humoral responses, can be attained by rDTI which allowed for maximal antigen exposure from staggered parasitic developmental stages. The data suggest that rDTI can be used as a model to study host-parasite interactions and identify parasite antigens responsible for eliciting host protective immune responses.

Ostertagia ostertagi Mediates Early Host Immune Responses via Macrophage and Toll-Like Receptor Pathways.

Ostertagia ostertagi is an abomasal parasite with significant economic impact on the cattle industry. Early host immune responses are poorly understood. Here, we examined time course expression of Toll-like receptors (TLRs) in peripheral blood mononuclear cells (PBMC) during infection where PBMC macrophages (Mϕ) generated both pro- and anti-inflammatory responses when incubated with excretory/secretory products (ESP) from fourth-stage larvae (OoESP-L4) or adult worms (OoESP-Ad). First, changes in cell morphology clearly showed that both OoESP-L4 and OoESP-Ad activated PBMC-Mϕ in vitro, resulting in suppressed CD40 and increased CD80 expression. Expression of mRNAs for TLR1, -4, -5, and -7 peaked 7 days postinfection (dpi) (early L4), decreased by 19 dpi (postemergent L4 and adults) and then increased at 27 dpi (late adults). The proinflammatory cytokine tumor necrosis factor alpha (TNF-α) (transcript and protein) increased in the presence of OoESP-Ad, and the anti-inflammatory cytokine interleukin 10 (IL-10) (protein) decreased in the presence of OoESP-L4 or OoESP-Ad; however, IL-10 mRNA was upregulated, and IL-6 (protein) was downregulated by OoESP-L4. When PBMC-Mϕ were treated with ligands for TLR4 or TLR5 in combination with OoESP-Ad, the transcripts for TNF-α, IL-1, IL-6, and IL-10 were significantly downregulated relative to treatment with TLR4 and TLR5 ligands only. However, the effects of TLR2 ligand and OoESP-Ad were additive, but only at the lower concentration. We propose that O. ostertagi L4 and adult worms utilize competing strategies via TLRs and Mϕ to confuse the immune system, which allows the worm to evade the host innate responses.

Salivary IgA: A biomarker for resistance to Teladorsagia circumcincta and a new estimated breeding value.

Teladorsagia circumcincta is the dominant nematode of sheep in cool, temperate climates. Faecal nematode egg counts (FEC) are widely used to identify the intensity of infection and as a measure of host resistance to nematodes. However due to density-dependent effects on worm fecundity the relationship between FEC and worm burden is not linear. In addition collecting FEC data is challenging on a practical level and there is a need for more reliable markers of resistance. There are two major known mechanisms of immunity to T. circumcincta: IgE against third stage larvae (L3) and IgA against fourth stage larvae (L4), which inhibits parasite growth. In this study salivary IgA responses were measured in over 5000 animals against L3 antigen by Enzyme Linked Immunosorbent Assay (ELISA). Antigen-specific IgA levels were negatively correlated with FEC (r=-0.26, SE = 0.02) and were heritable (h2 = 0.16, SE = 0.04) indicating that they can be used to identify resistant animals suitable for inclusion in selective breeding programs. Antigen-specific IgA responses were not negatively correlated with muscle depth. Our analyses indicate that selection for T. circumcincta L3 antigen-specific IgA is possible without impacting on the production traits for the Lleyn breed.

Characterization of IL-10-producing neutrophils in cattle infected with Ostertagia ostertagi.

IL-10 is a master regulator of immune responses, but its cellular source and function in cattle during the initial phase of immune priming have not been well established. Despite a massive B cell response in the abomasal draining lymph nodes in Ostertagia ostertagi (OO)-infected cattle, protective immunity is slow to develop, and partial protection requires years of repeated exposure. In addressing this problem, our initial hypothesis was that B cells produce IL-10 that downregulates the host protective immune response. However, our results showed that neutrophils made up the majority of IL-10-producing cells in circulation and in secondary lymphoid tissues, particularly the spleen (80%). Conversely, IL-10-producing B cells were rare. In addition, approximately 10% to 20% of the neutrophils in the blood and spleen expressed MHC II and were IL-10 negative, suggesting that neutrophils could also participate in antigen presentation. In vitro investigation of bovine neutrophils revealed that exposure thereof to OO extract increased IL-10 and MHC II expression in these cells in a dose-dependent manner, consistent with IL-10+/MHC II+ neutrophils detected in cattle shortly after experimental OO infection. Co-culture of untreated neutrophils with anti-CD3 antibody (Ab)-stimulated CD4+ T cells led to enhanced T cell activation; also, IL-10 depletion with neutralizing Ab enhanced the stimulatory function of neutrophils. OO extract depressed neutrophil stimulation of CD4+ T cells in the presence of IL-10-neutralizing Ab, suggesting that OO utilizes both IL-10-dependent and independent mechanisms to manipulate the bovine immune response. Finally, contact and viability were required for T cell-stimulatory neutrophil function. This report, to the best of our knowledge, is the first to demonstrate that neutrophil-derived IL-10 is directly involved in T cell regulation in cattle. Our data suggest that neutrophils and neutrophil-derived IL-10 are co-opted by nematode parasites and other pathogens to attenuate host immune responses and facilitate pathogen survival.

Short- and long-term association between individual levels of milk antibody against Ostertagia ostertagi and first-lactation heifer's production performances.

It is agreed that exposure of adult dairy cattle to helminths on pasture can negatively affect production performances as milking herd. Young animals, especially replacement heifers, represent the future of a dairy farm and are among the most vulnerable to helminth infections in a dairy herd. For this reason, dairy farmers tend to frequently treat heifers against helminths, although the impact of helminths on heifers' production performances is still poorly understood. Using different epidemiological and serological tools, this study examines the relationship between heifer exposure to helminths on pasture and production performances over time. During a one-year period, 1,454 individual milk samples were collected from first-lactation heifers in England and tested for Ostertagia ostertagi (O. ostertagi) antibodies. After controlling for other confounders, increasing milk antibody levels against O. ostertagi were significantly associated with decreased milk yield at sampling but not at day 305 of heifer lactation. We did not observe any relationship between milk antibody levels against O. ostertagi in heifers and yields in fat and protein. However, heifers with a high level of milk antibodies against O. ostertagi were more likely to produce dead calf at first calving and present a delay in second calving. Moreover, these heifers had significantly higher levels of milk antibodies against Mycobacterium paratuberculosis (M. paratuberculosis) during their first lactation and were more likely to die before the end of the study. We argue that epidemiological approaches can be useful but must be complemented by other methodologies to better understand the impact of helminth infections in dairy heifers. In order to address the complex dynamics of helminth infections in dairy cattle production we require more comprehensive approaches that include triangulation between data sources and interdisciplinary studies.

Bulk tank milk prevalence and production losses, spatial analysis, and predictive risk mapping of Ostertagia ostertagi infections in Mexican cattle herds.

This study investigated the prevalence, production losses, spatial clustering, and predictive risk mapping in different climate zones in five states of Mexico. The bulk tank milk samples obtained between January and April 2015 were analyzed for antibodies against Ostertagia ostertagi using the Svanovir ELISA. A total of 1204 farm owners or managers answered the questionnaire. The overall herd prevalence and mean optical density ratio (ODR) of parasite were 61.96% and 0.55, respectively. Overall, the production loss was approximately 0.542 kg of milk per parasited cow per day (mean ODR = 0.92, 142 farms, 11.79%). The spatial disease cluster analysis using SatScan software indicated that two high-risk clusters were observed. In the multivariable analysis, three models were tested for potential association with the ELISA results supported by climatic, environmental, and management factors. The final logistic regression model based on both climatic/environmental and management variables included the factors rainfall, elevation, land surface temperature (LST) day, and parasite control program that were significantly associated with an increased risk of infection. Geostatistical kriging was applied to generate a risk map for the presence of parasite in dairy cattle herds in Mexico. The results indicate that climatic and meteorological factors had a higher potential impact on the spatial distribution of O. ostertagi than the management factors.

Ostertagia ostertagi antibodies in bulk tank milk from dairy cattle in Italy: A nation-wide survey.

The objective of this study was to investigate the exposure to Ostertagia ostertagi in dairy cattle herds across Italy through measurement of antibody concentration in the bulk tank milk (BTM) and to evaluate the possible effect of regions, seasons and pasture management practices on the level of exposure to the parasite. The O. ostertagi antibody levels in milk were determined using a commercial ELISA kit (SVANOVIR® O. ostertagi-Ab) and expressed as optical density ratio (ODR). From March 2015 to September 2017, BTM samples were collected in 1209 dairy cattle farms located in 15 regions of Northern, Central and Southern Italy. As reported in previous studies, BTM samples were classified in three different categories according to the level of exposure to O. ostertagi as follows: (i) positive with ODR values >0.60; (ii) negative with ODR values <0.30 and (iii) grey zone with ODR values between 0.30 and 0.60. Finally, differences in ODR values between regions, seasons and herd management practices were studied using the one-way analysis of variance. The overall mean ODR revealed a value of 0.49 in Italy; in particular, dairy cattle farms located in Southern Italy showed the highest O. ostertagi BTM ODR values than the other regions (p < 0.05). The ODR values ranged from 0.45 in autumn to 0.53 in spring and the seasonal difference was significant (p < 0.05). Furthermore, a positive association was found between the ODR values and the access to pasture; herds with access to pasture showed significantly higher titres (p < 0.0001) of O. ostertagi antibodies in milk (mean ODR = 0.63) than in those in total-confinement housing (mean ODR = 0.42). This study, the first of its kind in Italy, will provide a quantitative assessment exposure to O. ostertagi of Italian dairy herds and represents a significant step forward in evidence-based medicine for dairy veterinarians, advisors and farmers.

A longitudinal study of gastrointestinal parasites in English dairy farms. Practices and factors associated with first lactation heifer exposure to Ostertagia ostertagi on pasture.

The gastrointestinal nematode Ostertagia ostertagi is an important cause of lost production, health, and welfare in cattle. Detailed records were obtained over a 5-yr period (2010-2015) by questionnaires and qualitative interviews to investigate the practices adopted by dairy farmers to control cattle helminth infections and the factors associated with heifer exposure to O. ostertagi on pasture. In total, 1,454 heifers' individual milk samples were collected over a 1-yr period (2014-2015) in 43 dairy farms in England and tested for O. ostertagi antibody by ELISA. Multilevel linear regression models were used to investigate the association between individual milk optical density ratio (ODR) against O. ostertagi and heifer management from birth to time of sampling. Farm and heifer median ODR against O. ostertagi were 0.98 (interquartile range = 0.76-1.02) and 0.64 (interquartile range = 0.42-0.84), respectively. The majority of heifers (88%) received an anthelmintic treatment before sampling in this study. After controlling for the effect of anthelmintic treatments, heifer individual milk ODR against O. ostertagi significantly increased with high stocking rate at first grazing and co-grazing with adult cows before calving. Conversely, heifer individual milk ODR against O. ostertagi significantly decreased when heifers had co-grazed with sheep and pasture grass had frequently been mowed. Overall, these results provide evidence to support targeting grazing management toward limiting the use of anthelmintics in dairy young stock to enable sustainable control of cattle helminth infections in England. However, to be accepted and adopted by farmers, these best practices would need to take into account farmers' perspectives and contextual challenges.

Significance of anti-CarLA salivary IgA antibody in first grazing season cattle naturally infected with gastrointestinal nematodes.

A carbohydrate larval surface antigen (CarLA) present on infective larvae of all trichostrongylid nematodes is a target antigen for host immunoglobulins (Ig). Levels of anti-CarLA salivary IgA antibody (CarLA-IgA) have been shown to be correlated to the level of protective immunity to GIN in sheep and deer but no information is available in cattle. The first objective of this study was to assess the pattern of CarLA-IgA response in 7 groups (G1-G7) of first grazing season cattle (FGSC) naturally infected with gastrointestinal nematodes. The second objective was to assess the phenotypic correlations between CarLA-IgA level, 3 parasitological indicators (faecal egg count-FEC, pepsinogen level, serum anti-O. ostertagi IgG antibody level-OstertagiaIgG), a clinical indicator (diarrhea score) and average daily weight gain (ADWG). Overall, CarLA-IgA response gradually increased over grazing season and showed large variations in speed and magnitude both between and within groups. Based on the mean group CarLA-IgA response pattern, the 7 groups could be allocated to 3 different classes: (i) 'Late High' class characterized by a high response at housing (G1 and G2); (ii) 'Low' class with a low response over time (G3, G4 and G5); and (iii) 'Early' class with an high initial then stable response (G6 and G7). This classification was consistent with the grazing management practices. In the 'Late High' class, the mean CarLA-IgA at housing was 6.05units/mL and negatively correlated with FEC while no correlation was seen with the other indicators nor ADWG. In the 'Low' class, CarLA response at housing was low (1.95units/mL) and mainly positively correlated with OstertagiaIgG. In the 'Early' class, mean CarLA-IgA ranged from 1.32 to 1.86units/mL during the grazing season and positive correlations were seen with parasitological and clinical indicators. These results suggest that, according to the intensity of larval challenge occurring during the first grazing season, CarLA-IgA response in cattle could be either an indicator of the early manifestation of immunity (FEC decreases) or the reflection of exposure to GIN.

Design and evaluation of multi-indicator profiles for targeted-selective treatment against gastrointestinal nematodes at housing in adult dairy cows.

Targeted-selective treatments against gastrointestinal nematode (GIN) in adult dairy cows require the identification of "cows to treat", i.e. cows whose milk production (MP) would increase after treatment. This study aimed at quantifying the ability of multi-indicator profiles to identify such cows. A randomized controlled clinical trial was conducted at housing in 25 French pasturing dairy herds. In each herd, treated cows received fenbendazole orally, control cows remained untreated. Daily MP was recorded and the MP variation between the pre- and post-visit periods was calculated (ΔMP) for each cow. ΔMP was modelled with control cows data (n=412) (piecewise linear mixed model). Estimated parameters were applied to treated cows data (n=414) to predict the expected ΔMP in treated cows if they had not been treated. Treated cows with an observed ΔMP (with treatment) higher than the expected ΔMP (without treatment) were labelled as "cows to treat". Herds where at least 50% of the young cows were "cows to treat" were qualified as "herds to target". To characterize such cows and herds, the available candidate indicators were (i) at the cow-level: parity, stage of lactation and production level, faecal egg count (FEC), serum pepsinogen level and anti-Ostertagia antibody level (expressed as ODR); (ii) at the herd-level: bulk tank milk (BTM) Ostertagia ODR, Time of Effective Contact (TEC, in months) with GIN infective larvae before the first calving, and percentage of positive FEC. These indicators were tested one-by-one or in combination to assess their ability to characterize "herds to target" and "cows to treat" (Chi-square tests). 115 out of 414 treated cows (27.8%) were considered as "cows to treat", and 9 out of 22 herds were qualified as "herds to target". The indicators retained to profile such cows and herds were the parity, the production level, the BTM Ostertagia ODR and the TEC. Multi-indicator profiles were much more specific than single indicator profiles, induced lower treatment rates, thereby minimizing the selection pressure on parasite populations. Particularly, to target a herd, the specificity was better with the profile "high BTM Ostertagia ODR and low-TEC" than with the BTM ODR value taken into account alone. The targeted-selective treatment of "young cows, belonging to herds with a high BTM ODR at housing and a low TEC" appeared as a pertinent solution, enabling a global approach for the control of GIN infection in which GIN control in heifers is connected to GIN control in adult cows.

Climate-driven longitudinal trends in pasture-borne helminth infections of dairy cattle.

Helminth parasites of grazing ruminants are highly prevalent globally and impact negatively on animal productivity and food security. There is a growing concern that climate change increases helminth disease frequency and intensity. In Europe, these concerns stem from case reports and theoretical life cycle models assessing the effects of climate change scenarios on helminth epidemiology. We believe this study is the first to investigate climate-driven trends in helminth infections of cattle on a cohort of randomly selected farms. One thousand, six hundred and eighty dairy farms were monitored over an 8year period for the two major helminth infections in temperate climate regions and climate-driven trends were investigated by multivariable linear mixed models. The general levels of exposure to Fasciola hepatica decreased over the study period while those to Ostertagia ostertagi increased, and this could at least be partially explained by meteorological factors (i.e. the number of rainy (precipitation >1mm) and warm days (average daily temperature >10°C) in a year). The longitudinal trends varied according to the altitude and the agricultural region of the farm. This study shows that longitudinal epidemiological data from sentinel farms combined with meteorological datasets can significantly contribute to understanding the effects of climate on infectious disease dynamics. When local environmental conditions are taken into account, the effects of climate change on disease dynamics can also be understood at more local scales. We recommend setting up a longitudinal sampling strategy across Europe in order to monitor climate-driven changes in helminth disease risk to inform adaptation strategies to promote animal health and productivity.

A simulation model to investigate interactions between first season grazing calves and Ostertagia ostertagi.

A dynamic, deterministic model was developed to investigate the consequences of parasitism with Ostertagia ostertagi, the most prevalent and economically important gastrointestinal parasite of cattle in temperate regions. Interactions between host and parasite were considered to predict the level of parasitism and performance of an infected calf. Key model inputs included calf intrinsic growth rate, feed quality and mode and level of infection. The effects of these varied inputs were simulated on a daily basis for key parasitological (worm burden, total egg output and faecal egg count) and performance outputs (feed intake and bodyweight) over a 6 month grazing period. Data from published literature were used to parameterise the model and its sensitivity was tested for uncertain parameters by a Latin hypercube sensitivity design. For the latter each parameter tested was subject to a 20% coefficient of variation. The model parasitological outputs were most sensitive to the immune rate parameters that affected overall worm burdens. The model predicted the expected larger worm burdens along with disproportionately greater body weight losses with increasing daily infection levels. The model was validated against published literature using graphical and statistical comparisons. Its predictions were quantitatively consistent with the parasitological outputs of published experiments in which calves were subjected to different infection levels. The consequences of model weaknesses are discussed and point towards model improvements. Future work should focus on developing a stochastic model to account for calf variation in performance and immune response; this will ultimately be used to test the effectiveness of different parasite control strategies in naturally infected calf populations.

Host protective ASP-based vaccine against the parasitic nematode Ostertagia ostertagi triggers NK cell activation and mixed IgG1-IgG2 response.

The mucus-dwelling parasite Ostertagia ostertagi is one of the most important gastrointestinal nematodes in cattle. Our group has previously demonstrated the protective capacity of a vaccine against this parasite based on a native activation-associated secreted protein ASP1 (nASP) in combination with the saponin adjuvant QuilA. The aim of the current study was to analyse the effect of both antigen and adjuvant on the cellular and humoral vaccine-induced immune responses by comparing the native ASP to a recombinant version expressed in Pichia pastoris (pASP) and replacing QuilA by Al(OH)3. Immunization of cattle with the protective nASP+QuilA vaccine was associated with antigen-induced proliferation of natural killer (NK) cells combined with IFN-γ secretion and the induction of a mixed IgG1/IgG2 antibody response. ASP-specific activation and proliferation of NK cells was also observed in mice following the same vaccination regime. Replacing QuilA by Al(OH)3 or nASP by pASP significantly decreased the capacity of the vaccines to trigger both NK cell activation and antibody responses and failed to induce protection against a challenge infection. Reduction of the structurally anchoring disulphide bonds of the nASP completely abolished its ability to induce NK cell activation and antibody responses, highlighting the importance of protein conformation for the immunostimulatory activity.

Integrating immune mechanisms to model nematode worm burden: an example in sheep.

Gastrointestinal nematodes represent important sources of economic losses in farmed ruminants, and the increasing frequency of anthelmintic resistance requires an increased ability to explore alternative strategies. Theoretical approaches at the crossroads of immunology and epidemiology are valuable tools in that context. In the case of Teladorsagia circumcincta in sheep, the immunological mechanisms important for resistance are increasingly well-characterized. However, despite the existence of a wide range of theoretical models, there is no framework integrating the characteristic features of this immune response into a tractable phenomenological model. Here, we propose to bridge that gap by developing a flexible modelling framework that allows for variability in nematode larval intake which can be used to track the variations in worm burdens. We parameterize this model using data from trickle infection of sheep and show that using simple immunological assumptions, our model can capture the dynamics of both adult worm burdens and nematode fecal egg counts. In addition, our analysis reveals interesting dose-dependent effects on the immune response. Finally, we discuss potential developments of this model and highlight how an improved cross-talk between empiricists and theoreticians would facilitate important advances in the study of infectious diseases.

Applying a kinetic method to an indirect ELISA measuring Ostertagia ostertagi antibodies in milk.

Indirect enzyme-linked immunosorbent assays (ELISAs) are frequently run as endpoint ELISAs (e-ELISAs). However, kinetic ELISAs (k-ELISAs) have certain advantages over e-ELISAs. The objective of this study was to understand the relationship between e-ELISA and k-ELISA results. Specifically, to determine whether it was possible to run both k-ELISA and e-ELISA on the same plate and establish an appropriate time interval for k-ELISA measurements. A normalization method for k-ELISA slopes (slope ratio) is proposed. Using an indirect e-ELISA test measuring antibodies against Ostertagia ostertagi in milk from dairy cattle, we found that running a k-ELISA had no effect on optical density ratio results of an e-ELISA on the same plate, and that agreement was very strong at 10, 15, and 28 min, allowing for a reduction in the total processing time for ELISA tests.

Les épreuves immunoenzymatiques indirectes (ELISA) sont fréquemment effectuées comme ELISA avec un point limite (e-ELISA). Toutefois, une épreuve ELISA cinétique (k-ELISA) a certains avantages par rapport à une e-ELISA. L'objectif de la présente étude était de comprendre la relation entre les résultats d'une e-ELISA et ceux d'une k-ELISA. Spécifiquement, déterminer s'il est possible de réaliser simultanément sur la même plaque une épreuve k-ELISA et une épreuve e-ELISA et d'établir un intervalle de temps approprié pour les mesures de k-ELISA. Une normalisation de la méthode pour les pentes des k-ELISA (rapport de pente) est proposée. En utilisant une épreuve e-ELISA indirecte pour mesurer les anticorps dirigés contre Ostertagia ostertagi dans le lait de bovins laitiers, nous avons trouvé que d'effectuer une k-ELISA n'avait aucun effet sur les résultats des ratios de densité optique d'une e-ELISA effectuée sur la même plaque, et que l'accord était très élevé à 10, 15, et 28 min, permettant ainsi une réduction du temps de traitement total pour les épreuves ELISA.(Traduit par Docteur Serge Messier).

Prevalence and seasonality of bulk milk antibodies against Dictyocaulus viviparus and Ostertagia ostertagi in Irish pasture-based dairy herds.

Infections with Dictyocaulus viviparus and Ostertagia ostertagi nematode parasites are of importance to bovine health and production in temperate areas across the world. Losses due to these parasites in dairy herds can be considerable due to decreased milk productivity and fertility. However, information on current epidemiological patterns in Irish dairy herds is limited. Bulk milk samples were collected from a total of 319 dairy farms across the Republic of Ireland. The D. viviparus samples were tested with an ELISA based on recombinant major sperm protein, while the O. ostertagi samples were tested with an ELISA based on crude saline extract, whole worm O. ostertagi antigen. Management data were collected from the farms using a questionnaire. Logistic regression was used to find significant associations between the presence of antibodies against D. viviparus and O. ostertagi and management factors. The overall prevalence of D. viviparus infection was 62.8%, while over 98% of herds had antibodies to O. ostertagi at the specified cut-off. Both D. viviparus and O. ostertagi antibodies were highest in November, which could be explained by the accumulated uptake of larvae through the grazing season. In herds of farmers that dosed their in-calf heifers with anthelmintics were significantly more likely to be positive for antibodies against D. viviparus infection. This study highlights that both D. viviparus and O. ostertagi infections are widespread in dairy herds in Ireland throughout the grazing season.

The parasitic phase of Ostertagia ostertagi: quantification of the main life history traits through systematic review and meta-analysis.

Predictive models of parasite life cycles increase our understanding of how parasite epidemiology is influenced by global changes and can be used to support decisions for more targeted worm control. Estimates of parasite population dynamics are needed to parameterize such models. The aim of this study was to quantify the main life history traits of Ostertagia ostertagi, economically the most important nematode of cattle in temperate regions. The main parameters determining parasite density during the parasitic phase of O. ostertagi are (i) the larval establishment rate, (ii) hypobiosis rate, (iii) adult mortality and (iv) female fecundity (number of eggs laid per day per female). A systematic review was performed covering studies from 1962 to 2007, in which helminth-naïve calves were artificially infected with O. ostertagi. The database was further extended with results of unpublished trials conducted at the Laboratory for Parasitology of Ghent University, Belgium. Overall inverse variance weighted estimates were computed for each of the traits through random effects models. An average establishment rate (±S.E.) of 0.269±0.022 was calculated based on data of 27 studies (46 experiments). The establishment rate declined when infection dose increased and was lower in younger animals. An average proportion of larvae entering hypobiosis (±S.E.) of 0.041 (±0.009) was calculated based on 27 studies (54 experiments). The proportion of ingested larvae that went into hypobiosis was higher in animals that received concomitant infections with nematode species other than O. ostertagi (mixed infections). An average daily adult mortality (±S.E.) of 0.028 (±0.002) was computed based on data from 28 studies (70 experiments). Adult mortality was positively correlated with infection dose. A daily fecundity (±S.E.) of 284 (±45) eggs per female was found based on nine studies (10 experiments). The average female sex ratio of O. ostertagi based on individual animal data (n=75) from six different studies was estimated to be 0.55. We believe that this systematic review is the first to summarise the available data on the main life history traits of the parasitic phase of O. ostertagi. In conclusion, this meta-analysis provides novel estimates for the parameterization of life cycle-based transmission models, explicitly reports measures of variance around these estimates, gives evidence for density dependence of larval establishment and adult mortality, shows that host age affects larval establishment and, to our knowledge, provides the first evidence for O. ostertagi of a female-biased sex ratio.