The influence of a Cooperia oncophora priming on a concurrent challenge with Ostertagia ostertagi and C. oncophora in calves

Novel epidemiological model of gastrointestinal nematode infection to assess grazing cattle resilience by integrating host growth, parasite, grass and environmental dynamics

Gastrointestinal nematode (GIN) infections are ubiquitous and often cause morbidity and reduced performance in livestock. Emerging anthelmintic resistance and increasing change in climate patterns require evaluation of alternatives to traditional treatment and management practices. Mathematical models of parasite transmission between hosts and the environment have contributed towards the design of appropriate control strategies in ruminants, but have yet to account for relationships between climate, infection pressure, immunity, resources, and growth. Here, we develop a new epidemiological model of GIN transmission in a herd of grazing cattle, including host tolerance (body weight and feed intake), parasite burden and acquisition of immunity, together with weather-dependent development of parasite free-living stages, and the influence of grass availability on parasite transmission. Dynamic host, parasite and environmental factors drive a variable rate of transmission. Using literature sources, the model was parametrised for Ostertagia ostertagi, the prevailing pathogenic GIN in grazing cattle populations in temperate climates. Model outputs were validated on published empirical studies from first season grazing cattle in northern Europe. These results show satisfactory qualitative and quantitative performance of the model; they also indicate the model may approximate the dynamics of grazing systems under co-infection by O. ostertagi and Cooperia oncophora, a second GIN species common in cattle. In addition, model behaviour was explored under illustrative anthelmintic treatment strategies, considering impacts on parasitological and performance variables. The model has potential for extension to explore altered infection dynamics as a result of management and climate change, and to optimise treatment strategies accordingly. As the first known mechanistic model to combine parasitic and free-living stages of GIN with host feed-intake and growth, it is well suited to predict complex system responses under non-stationary conditions. We discuss the implications, limitations and extensions of the model, and its potential to assist in the development of sustainable parasite control strategies.

A Review of Dung Beetle Introductions in the Antipodes and North America: Status, Opportunities, and Challenges

Following the introduction of cattle, exotic dung beetles (Coleoptera: Aphodiidae, Geotrupidae, Scarabaeidae) were imported into the Antipodes (Australia and New Zealand) and North America (primarily the United States) to accelerate the degradation of cattle dung on pastures. The history of dung beetle introductions between the two regions is similar but has not previously been assessed: this is important as new introductions are continuing in the regions. Here, we review these introduction programs, report on their current status, and discuss methodological advances. In doing so, we examine the accidental introduction of exotic (i.e., adventive) species and the contribution of both deliberately introduced and adventive species to endemic dung beetle faunas. Further, we provide a list of pest and parasite species whose populations can be reduced by dung beetle activity. We also identify a combined total of 37 introduced and 47 adventive dung beetle species that have become established in the Antipodes and North America, with exotic species dominating dung beetle assemblages from pasture habitats. Climatic and edaphic matches, the size of founding populations, abiotic and biotic stressors, and the time of year when releases are made are all critical determinants that affect the success of dung beetle introduction programs. Finally, we discuss opportunities, plus the risks and challenges associated with dung beetle introductions. We hope that this review will aid in the success of future introduction programs, either to enhance ecosystem services in areas that they are needed, or potentially to reestablish native species in regions where they have been extirpated.

Host effects on the free-living stages of Haemonchus contortus

A group of 5 lambs (Host 1-5) was infected with the same batch of Haemonchus contortus and after patency individual faecal samples were collected, separately incubated at 23 °C for 14 days and third stage larvae collected through Baermannisation. Life-history traits were compared between larvae from different hosts: the length of the larvae was measured by microscope image analysis, larval survival in water at 35 °C, larval susceptibility to ivermectin (EC₅₀) in a migration assay, the proportion of larvae exsheathing in vitro and the proportion establishing to the adult stage in young lambs. For all traits there were significant differences between the host animals, with larvae from specific hosts following a consistent pattern of displaying the highest or lowest trait results. Compared with larvae from Host 1 the larvae from Host 5 were () shorter (741-692 μm, p < 0.05), had a longer median survival at 35 °C (3.6-6.4 days, p < 0.05), were less susceptible to ivermectin (EC₅₀ of 1.2 v 4.5 μM, p < 0.05), exsheathed to a lesser degree (83.6-58 %, p < 0.05), but showed a higher establishment rate in the consecutive host (15.2-31.4 %, p < 0.05). Regarding the survival time, anthelmintic susceptibility (under most commercial farming practices) and establishment rate as indicators for fitness, the parasites populating Host 5 produced progeny of higher fitness. The findings indicate that the host animal of the parental parasite generation has a significant effect on the parasite progeny.

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.

The vitamin D receptor and inducible nitric oxide synthase associated pathways in acquired resistance to Cooperia oncophora infection in cattle

Cooperia oncophora is an economically important gastrointestinal nematode in ruminants. Acquired resistance to Cooperia oncophora infection in cattle develops rapidly as a result of prior infections. Naïve cattle, when given a primary infection of high-dose infective L3 larvae, develop a strong immunity to subsequent reinfection. Compared to primary infection, reinfection resulted in a marked reduction in worm establishment. In order to understand molecular mechanisms underlying the development of acquired resistance, we characterized the transcriptomic responses of the bovine small intestine to a primary infection and reinfection. A total of 23 pathways were significantly impacted during infection. The vitamin D receptor activation was strongly induced only during reinfection, suggesting that this pathway may play an important role in the development of acquired resistance via its potential roles in immune regulation and intestinal mucosal integrity maintenance. The expression of inducible nitric oxide synthase (NOS2) was strongly induced during reinfection but not during primary infection. As a result, several canonical pathways associated with NOS2 were impacted. The genes involved in eicosanoid synthesis, including prostaglandin synthase 2 (PTGS2 or COX2), remained largely unchanged during infection. The rapid development of acquired resistance may help explain the lack of relative pathogenicity by Cooperia oncophora infection in cattle. Our findings facilitate the understanding of molecular mechanisms underlying the development of acquired resistance, which could have an important implication in vaccine design.

T-cell mediated immune responses in calves primary-infected or re-infected with Cooperia oncophora: similar effector cells but different timing

Cooperia oncophora is the most prevalent intestinal nematode of cattle occurring in Western Europe. Primary infection with 100000 third stage infective larvae (L3) induces acquired immunity in a high proportion of the animals but there is little information on immunity against re-infection. In the current experiment, the contribution of the T-cell mediated immunity in protection against re-infection with C. oncophora was investigated in detail. Priming elicited long-lasting protective immunity that was evidenced by a significantly decreased worm burden and egg excretion in primed animals compared to challenge control animals. Lymphocyte proliferation tests with excretory/secretory products (ESP) of C. oncophora and with three distinct ESP fractions indicated an enhanced reactivity in primed animals and suggested that by fractionating of ESP we selected for proteins involved in protective immunity against re-infection with C. oncophora. Phenotypic analysis of T cell subsets at diverse anatomical locations revealed that the enhanced reactivity of lymphocytes from peripheral blood and lymph nodes of the infected animals coincided with a significantly increased frequency of CD4(+) cells at these locations but a deceased frequency of CD4(+) cells in the lamina propria. These findings were independent of the immune status of the animals but more pronounced in the primed animals than in the challenge control animals. In addition we demonstrated that primary and secondary infections with C. oncophora were associated with two waves of eosinophils and that the kinetics of this cell population differed as a result of priming. Based on the observed correlations we propose that the early increase of eosinophils is T cell independent and merely a consequence of inflammation in the parasitised gut. In contrast, the second wave of eosinophils depends upon CD4(+) cells and correlations with parasitological parameters at this time point support a role of eosinophils as effector cells against adult stages of C. oncophora.