The role of inhibited development in the epidemiology of Ostertagia infections

Behaviour is more important than thermal performance for an Arctic host-parasite system under climate change

Climate change is affecting Arctic ecosystems, including parasites. Predicting outcomes for host-parasite systems is challenging due to the complexity of multi-species interactions and the numerous, interacting pathways by which climate change can alter dynamics. Increasing temperatures may lead to faster development of free-living parasite stages but also higher mortality. Interactions between behavioural plasticity of hosts and parasites will also influence transmission processes. We combined laboratory experiments and population modelling to understand the impacts of changing temperatures on barren-ground caribou (Rangifer tarandus) and their common helminth (Ostertagia gruehneri). We experimentally determined the thermal performance curves for mortality and development of free-living parasite stages and applied them in a spatial host-parasite model that also included behaviour of the parasite (propensity for arrested development in the host) and host (long-distance migration). Sensitivity analyses showed that thermal responses had less of an impact on simulated parasite burdens than expected, and the effect differed depending on parasite behaviour. The propensity for arrested development and host migration led to distinct spatio-temporal patterns in infection. These results emphasize the importance of considering behaviour-and behavioural plasticity-when projecting climate-change impacts on host-parasite systems.

A participatory surveillance of marsh deer (Blastocerus dichotomus) morbidity and mortality in Argentina: first results

Background

In an era of unprecedented socio-ecological changes, managing wildlife health demands high-quality data collection and the engagement of local communities. Blastocerus dichotomus, the largest South American deer, is Vulnerable to extinction mainly due to habitat loss. Diseases have been recognised as a potential threat, and winter mortality has been historically described in marsh deer populations from Argentina. Field difficulties have, however, prevented in-depth studies of their health status.

Results

Between May 2014 and April 2017, we investigated marsh deer morbidity and mortality in the two largest populations in Argentina. We collected data by means of a passive surveillance system that involved a network of researchers, field partners (veterinarians, park rangers, and local community), and decision makers. We sampled marsh deer during as well as outside mortality events. A total of 44 marsh deer with different body condition scores were evaluated. We obtained haematology and biochemistry values from animals with good body condition score. Marsh deer with poor body condition had a high burden of the ticks Amblyomma triste and Rhipicephalus microplus. Vector-borne agents such as Theileria cervi, Trypanosoma theileri, Trypanosoma evansi, Ehrlichia chaffeensis, Anaplasma platys, Anaplasma odocoilei, Anaplasma marginale, and Candidatus Anaplasma boleense were also found. Haemonchus spp., Ostertagia spp., and Trichostrongylus spp. were the most frequent gastrointestinal parasites in deer with poor body condition. A Multiple Correspondence Analysis reinforced a possible association of winter period with lower body score condition, high tick loads, infection with E. chaffeensis, and presence of harmful gastrointestinal parasites.

Conclusions

Our approach allowed the establishment of a participatory surveillance network of marsh deer morbidity and mortality in Argentina. We report and analyse the first data obtained opportunistically within the framework of this network, providing information on the infectious and parasitic agents in marsh deer populations. The occurrence of Fasciola hepatica and Leptospira interrogans serovar pyrogenes is reported for the first time in wild marsh deer from Argentina. Our data will be useful to improve the interpretation of future mortality events. The field implementation of a surveillance network is key to a holistic approach to wildlife diseases.

A Revised Checklist of Cooperia Nematodes (Trichostrogyloidea), Common Parasites of Wild and Domestic Ruminants

This review updates the current knowledge on the taxonomy of intestinal nematodes of the genus Cooperia parasitizing in wild and domestic ruminants. The emphasis is put on revision of 19 valid species belonging to the genus. This analysis focuses on main features of the genus Cooperia, including its geographic occurrence and the life cycle details. The most widespread congeners are Cooperia curticei, C. oncophora, C. pectinata, and C. punctata, having nearly worldwide distribution. The fifth species, referred by electronic databases from the European territory as Cooperia asamatiSpiridonov, 1985, is unveiled here originally as nomen nudum.

Adaptations, life-history traits and ecological mechanisms of parasites to survive extremes and environmental unpredictability in the face of climate change

Climate change is increasing weather unpredictability, causing more intense, frequent and longer extreme events including droughts, precipitation, and both heat and cold waves. The performance of parasites, and host-parasite interactions, under these unpredictable conditions, are directly influenced by the ability of parasites to cope with extremes and their capacity to adapt to the new conditions. Here, we review some of the structural, behavioural, life history and ecological characteristics of parasitic nematodes that allow them to persist and adapt to extreme and changing environmental conditions. We focus primarily, but not exclusively, on parasitic nematodes in the Arctic, where temperature extremes are pronounced, climate change is happening most rapidly, and changes in host-parasite interactions are already documented. We discuss how life-history traits, phenotypic plasticity, local adaptation and evolutionary history can influence the short and long term response of parasites to new conditions. A detailed understanding of the complex ecological processes involved in the survival of parasites in extreme and changing conditions is a fundamental step to anticipate the impact of climate change in parasite dynamics.

GLOWORM-PARA: a flexible framework to simulate the population dynamics of the parasitic phase of gastrointestinal nematodes infecting grazing livestock

Gastrointestinal nematodes are a significant threat to the economic and environmental sustainability of keeping livestock, as adequate control becomes increasingly difficult due to the development of anthelmintic resistance in some systems and climate-driven changes to infection dynamics. To mitigate any negative impacts of climate on gastrointestinal nematode epidemiology and slow anthelmintic resistance development, there is a need to develop effective, targeted control strategies that minimise the unnecessary use of anthelmintic drugs and incorporate alternative strategies such as vaccination and evasive grazing. However, the impacts climate and gastrointestinal nematode epidemiology may have on the optimal control strategy are generally not considered, due to lack of available evidence to drive recommendations. Parasite transmission models can support control strategy evaluation to target field trials, thus reducing the resources and lead-time required to develop evidence-based control recommendations incorporating climate stochasticity. Gastrointestinal nematode population dynamics arising from natural infections have been difficult to replicate and model applications have often focussed on the free-living stages. A flexible framework is presented for the parasitic phase of gastrointestinal nematodes, GLOWORM-PARA, which complements an existing model of the free-living stages, GLOWORM-FL. Longitudinal parasitological data for two species that are of major economic importance in cattle, Ostertagia ostertagi and Cooperia oncophora, were obtained from seven cattle farms in Belgium for model validation. The framework replicated the observed seasonal dynamics of infection in cattle on these farms and overall, there was no evidence of systematic under- or over-prediction of faecal egg counts. However, the model under-predicted the faecal egg counts observed on one farm with very young calves, highlighting potential areas of uncertainty that may need further investigation if the model is to be applied to young livestock. The model could be used to drive further research into alternative parasite control strategies such as vaccine development and novel treatment approaches, and to understand gastrointestinal nematode epidemiology under changing climate and host management.

Nematode-coccidia parasite co-infections in African buffalo: Epidemiology and associations with host condition and pregnancy

Co-infections are common in natural populations and interactions among co-infecting parasites can significantly alter the transmission and host fitness costs of infection. Because both exposure and susceptibility vary over time, predicting the consequences of parasite interactions on host fitness and disease dynamics may require detailed information on their effects across different environmental (season) and host demographic (age, sex) conditions. This study examines five years of seasonal health and co-infection patterns in African buffalo (Syncerus caffer). We use data on two groups of gastrointestinal parasites, coccidia and nematodes, to test the hypothesis that co-infection and season interact to influence (1) parasite prevalence and intensity and (2) three proxies for host fitness: host pregnancy, host body condition, and parasite aggregation. Our results suggest that season-dependent interactions between nematodes and coccidia affect the distribution of infections. Coccidia prevalence, coccidia intensity and nematode prevalence were sensitive to factors that influence host immunity and exposure (age, sex, and season) but nematode intensity was most strongly predicted by co-infection with coccidia and its interaction with season. The influence of co-infection on host body condition and parasite aggregation occurred in season-dependent manner. Co-infected buffalo in the early wet season were in worse condition, had a less aggregated distribution of nematode parasites, and lower nematode infection intensity than buffalo infected with nematodes alone. We did not detect an effect of infection or co-infection on host pregnancy. These results suggest that demographic and seasonal variation may mediate the effects of parasites, and their interactions, on the distribution and fitness costs of infection.

A walk on the tundra: Host-parasite interactions in an extreme environment

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Climate change is altering host–parasite interactions in the Arctic.

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Changing ecological barriers reflect climate warming.

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Metabolic Theory of Ecology advances understanding of host–parasite interactions.

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Diversity emerges from host/parasite biogeographic/ecologic history.

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Insights gained from the Arctic apply to more complex systems.

Climate change is occurring very rapidly in the Arctic, and the processes that have taken millions of years to evolve in this very extreme environment are now changing on timescales as short as decades. These changes are dramatic, subtle and non-linear. In this article, we discuss the evolving insights into host–parasite interactions for wild ungulate species, specifically, muskoxen and caribou, in the North American Arctic. These interactions occur in an environment that is characterized by extremes in temperature, high seasonality, and low host species abundance and diversity. We believe that lessons learned in this system can guide wildlife management and conservation throughout the Arctic, and can also be generalized to more broadly understand host–parasite interactions elsewhere. We specifically examine the impacts of climate change on host–parasite interactions and focus on: (I) the direct temperature effects on parasites; (II) the importance of considering the intricacies of host and parasite ecology for anticipating climate change impacts; and (III) the effect of shifting ecological barriers and corridors. Insights gained from studying the history and ecology of host–parasite systems in the Arctic will be central to understanding the role that climate change is playing in these more complex systems.

Exploiting parallels between livestock and wildlife: Predicting the impact of climate change on gastrointestinal nematodes in ruminants

Global change, including climate, policy, land use and other associated environmental changes, is likely to have a major impact on parasitic disease in wildlife, altering the spatio-temporal patterns of transmission, with wide-ranging implications for wildlife, domestic animals, humans and ecosystem health. Predicting the potential impact of climate change on parasites infecting wildlife will become increasingly important in the management of species of conservation concern and control of disease at the wildlife-livestock and wildlife-human interface, but is confounded by incomplete knowledge of host-parasite interactions, logistical difficulties, small sample sizes and limited opportunities to manipulate the system. By exploiting parallels between livestock and wildlife, existing theoretical frameworks and research on livestock and their gastrointestinal nematodes can be adapted to wildlife systems. Similarities in the gastrointestinal nematodes and the life-histories of wild and domestic ruminants, coupled with a detailed knowledge of the ecology and life-cycle of the parasites, render the ruminant-GIN host-parasite system particularly amenable to a cross-disciplinary approach.

Parasites in ungulates of Arctic North America and Greenland: a view of contemporary diversity, ecology, and impact in a world under change

Parasites play an important role in the structure and function of arctic ecosystems, systems that are currently experiencing an unprecedented rate of change due to various anthropogenic perturbations, including climate change. Ungulates such as muskoxen, caribou, moose and Dall's sheep are also important components of northern ecosystems and are a source of food and income, as well as a focus for maintenance of cultural traditions, for northerners. Parasites of ungulates can influence host health, population dynamics and the quality, quantity and safety of meat and other products of animal origin consumed by people. In this article, we provide a contemporary view of the diversity of nematode, cestode, trematode, protozoan and arthropod parasites of ungulates in arctic and subarctic North America and Greenland. We explore the intricate associations among host and parasite assemblages and identify key issues and gaps in knowledge that emerge in a regime of accelerating environmental transition.

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.

Effects of pastures' re-wetting on endoparasites in cattle in northern Germany

The influence of re-wetting of pastures on the occurrence of important endoparasites in cattle was monitored over the course of three years. The study was conducted on a peninsula at the German North-Sea Coast. The cattle were stabled from November to April. During summer season, they were kept on pastures included in a nature protection program differentiating between three states of re-wetting. Faecal samples from randomly selected animals were analysed with routine diagnostic methods for the occurrence of Eimeria spp., nematode and trematode eggs and lungworm larvae. Samples were taken three times per year: before turning out, in the middle of the grazing season and at the end. After a diagnostic and plausibility check, a total of 692 samples could be used for statistical analysis. The overall prevalence was 29.5% for Eimeria spp. and 42.2% for nematodes. Eggs of the liver fluke and lungworm larvae were only detected at very low levels. Statistical analyses were performed with a generalized linear model including the fixed effects wetting status, farm, year, and if it was the first summer on pasture for the animal. Significant influences on nematodes were detected for the stage of re-wetting, while Eimeria spp. were significantly affected by the grazing period. These findings indicate that the important parasites liver fluke and lungworm have not hitherto been affected at all by re-wetting measures. Furthermore, the prevalence of nematodes and Eimeria spp. did not increase. In conclusion, no clinical signs for parasitic diseases and no significantly elevated infection levels were shown after the third year of re-wetting, but even longer observations are essential to evaluate long-term consequences.

Arrested development of sheep strongyles: onset and resumption under field conditions of Central Europe

Two tracer tests were conducted between August 2004 and March 2007 at an ecological farm in western Bohemia. The first tracer test was performed for the summer-autumn grazing period (onset of arrested development), the second for spring (resumption of arrested development). In the first tracer test, the percentage of nematodes arresting development over the winter months reached 87.7% for Teladorsagia circumcincta, 66.7% for Haemonchus contortus, 89.9% for Nematodirus filicollis, 21.6% for Trichostrongylus axei, and 23.9% for both Trichostrongylus vitrinus and Trichostrongylus colubriformis. None of the arrested larvae were observed with species Cooperia curticei, Nematodirus battus, and Oesophagostomum venulosum. In the second tracer test, a significant increase of adult worms was discovered in March of species T. circumcincta and N. filicollis and Trichostrongylus spp. in February. Redundancy analysis and generalized linear models analyses have confirmed that environmental conditions play a crucial role in hypobiosis of sheep strongyles in the Czech Republic. The analysis of influences of various environmental factors revealed that the number of arrested larvae was negatively influenced by light-day length, sunshine, or daylight decrease (p < 0.01).

Trichostrongylus colubriformis rDNA polymorphism associated with arrested development

Polymerase chain reaction-restriction fragment length polymorphism) was performed on the cistron of rDNA in the two groups of infective larvae Trichostrongylus colubriformis-the population with and without ability to undergo arrested development. General primers designed by Caenorhabditis elegans rDNA were used for the amplification of the rDNA cistron between genes 18S and 28S. Amplified fragments were digested by using a series of restriction endonucleases. Hinc II restriction profiles unique for each T. colubriformis populations were observed, and therefore enzyme Hinc II appears to be useful for the determination of populations with and without the ability to undergo arrested development. Molecular markers of arrested development ability have not been studied on this part of rDNA before.

Diapause in parasitic nematodes: a review

This review considers in a selective way the literature on diapause in parasitic nematodes, concentrating on four species of animal parasites and three species of plant parasites. We define diapause as a developmental arrest which is temporarily irreversible, so development will not resume, even under favourable conditions, until some intrinsic changes have been completed. Our analysis recognises four stages in diapause. The first is induction, typically brought about by environmental signals (although diapause may be genetically programmed independently of the environment). These environmental signals typically do not have an immediate effect on development, but we recognise a second phase, which we call the diapause pathway, in which worms have been induced to enter diapause at a later developmental stage. Surprisingly, entry into the diapause pathway may under some circumstances be reversible. The third stage is diapause development, a period during which development is suspended, but some ill-understood process must be completed prior to the fourth stage, emergence from diapause. Although diapause development is complete, resumption of development may be further delayed because of conditions in the host or in the environment: the worm is once more capable of development, but development is prevented by unfavourable conditions extrinsic to the worm. These may include the immune state of the host or the total parasite burden in animal hosts.

Study on the inductive factors of hypobiosis of Ostertagia ostertagi in cattle

Two experiments were carried out to determine the causes producing the Ostertagia ostertagi hypobiosis phenomenon in cattle. In the first experiment, the effect of time on third-stage larvae in the environment was studied during a 2-year period. Three experimental paddocks contaminated with O. ostertagi eggs at different times of the year were used, and the levels of hypobiosis were recorded by using 'indicator' and 'tracer' calves. The results suggest that time as such is not a hypobiosis-inductive factor. The second experiment was conducted under laboratory conditions, where the effects of temperature and light on infective larvae were studied. Infective larvae were subjected to different conditions of temperature and light during 6 weeks, and then inoculated to parasite-naive calves, which were slaughtered after 4 weeks. Percentages of hypobiotic larvae in these calves varied from 3.5 to 94.8%, depending on the different storage conditions the larvae underwent before inoculation. Results suggest that increasing temperature and increasing time of light exposure simulating spring conditions would be the factors which act upon third-stage larvae inducing them to a later hypobiotic stage in the host.

Hypobiosis of Haemonchus contortus in natural infections of sheep and goats in a semi-arid area of Kenya

A total of 42 lambs, 42 kids, 21 ewes and 21 does were necropsied during an investigation of the epidemiology of Haemonchus contortus infection of sheep (Red Maasai) and goats (Small East African Goat) in a semi-arid area of Kenya. Availability and establishment of the infective stages were monitored by the necropsy of 21 tracer lambs and 21 tracer kids. Prevalence of H. contortus was over 90% in both sheep and goats and this species contributed to about 80% of the total worm burden. Only about 10% of the hypobiotic larvae were recovered from the mucosal digest whereas about 90% were recovered from the abomasal contents and washings, thereby suggesting that hypobiotic larvae may be loosely attached to the abomasal mucosa from which they may be dislodged during the processing of the abomasa for examination. Throughout the study, both adult worms and hypobiotic larvae were found in proportions that varied with seasons. Statistically, a higher proportion of hypobiotic larvae was found during the dry months than during the wet months, an indication that hypobiosis was an important feature in the survival of H. contortus during the dry months. Negligible worm burdens were acquired by the tracers during the short rains, suggesting that few H. contortus larvae survived on pasture in this season. The effectiveness of strategic control using ivermectin varied according to the timing in relation to the wet season. Treatment did not influence the seasonal pattern of hypobiosis but the treatment administered before the onset of the rains significantly reduced the numbers of both hypobiotic larvae and the adult worms. Treatment during the rains conferred a temporary relief of adult worm burden but had no impact on hypobiotic larvae.

Some aspects of inhibited development of trichostrongylids in ruminants

Inhibited development is an important aspect of the biology of some gastrointestinal nematodes of ruminants, particularly species of the subfamily Ostertagiinae and Haemonchus spp. There is a seasonality in the occurrence of the phenomenon. It tends to occur predominantly during the unfavourable season for the free-living stages. Thus 'winter' and 'summer-dry season' patterns of inhibition can be observed. Furthermore, the phenomenon is influenced by immunity of the host and by management factors. Different studies show conflicting results on the phenomenon of inhibition. This is examplified by studies related to H. contortus in small ruminants. Other studies indicate that large differences in propensity for inhibition can indeed occur in a single region. However, it has to be stressed that inadequate necropsy techniques can easily result in underestimation of the proportion of inhibited larvae, particularly in Haemonchus spp. in cattle. The macrocyclic lactones are highly effective against inhibited larvae of gastrointestinal nematodes. Treatment may even prevent establishment of inhibited larvae of Ostertagia and Trichostrongylus axei up to 1 month after treatment. The efficacy of benzimidazoles seems to be lower in the middle of the 'inhibition' period than at the beginning or the end. Some studies indicated that the presence of inhibited stages may be important for the build up of immunity. However, removal of high inhibited O. ostertagi burdens at housing does not impair development of immunity. Very little progress has been made on the molecular mechanisms of inhibited development.

Analysis of proteins related to conditioning for arrested development and differentiation in Haemonchus contortus by two-dimensional gel electrophoresis

The abundance of the majority of proteins of infectious third-stage larvae (L3) of Haemonchus contortus, conditioned for arrested development, remained unaltered. Only seven proteins showed quantitative differences as observed by two-dimensional gel electrophoresis. These differences were also observed in a laboratory strain which has lost the ability for arrested development. The abundance of two of these proteins increased dramatically during conditioning of larvae for 5-10 weeks. This coincided with the highest percentage of inhibited larvae in experimental infections. Moreover, the abundance of these proteins decreased again after prolonged conditioning (22 weeks). The abundance of the other 5 proteins was not correlated to the percentage of inhibition. We therefore conclude that these proteins are involved in the aging process of larvae. The changes in protein between free-living (L3) and parasitic stages (L4) were large and seem to reflect the large environmental changes experienced by the larvae when entering a mammalian host. Early fourth- (EL4) and late fourth- (LL4) stage larvae differed in 9 proteins. One protein was stage-specific for EL4. These results imply that only minor alterations do occur in these stages notwithstanding the large morphological differences between these larvae.

A comparison of early and mid grazing season suppressive anthelmintic treatments for first year grazing calves and their effects on natural and experimental infection during the second year

A comparison was made of the efficacy and parasitological sequelae over 2 years, of continuous and intermittent periods of anthelmintic suppression applied both early and in the middle of the first grazing season of calves. Five groups of 15 calves grazing separate paddocks within the same field were allotted to one of the following treatment regimes during their first year at grass: Group 1, untreated controls; Group 2, treated with ivermectin injections at 3, 8 and 13 weeks after turnout; Group 3, treated with ivermectin injections at 10, 15 and 20 weeks after turnout; Group 4, treated with a morantel slow release intraruminal bolus at turnout; Group 5, treated with a morantel slow release bolus at 10 weeks after turnout. Five animals from each group were slaughtered at the end of both grazing seasons. Two months after the end of the second season the remaining five calves were challenged with an experimental infection of 250,000 third-stage larvae (L3) of both Ostertagia ostertagi and Cooperia oncophora. All treatment regimes protected the respective calves from parasitic gastroenteritis. Over the 2 year observation period Groups 2 and 4 showed significantly better weight gain than other groups, and at the end of the first season, they were found to harbour significantly fewer O. ostertagi in the early fourth stage of development. During Year 1, Groups 2 and 3 excreted much lower percentages of Ostertagia spp. eggs than other groups. In Year 2, Group 2 excreted a higher percentage of Ostertagia spp. eggs although the total egg output was approximately half that of Group 1 during the same period. The results showed that the effects of anthelmintic suppression on egg output of different nematode species was affected by the activity of the anthelmintic used.

Isotype-specific serum antibody responses of sheep to Haemonchus contortus antigens

In total, 19 8-month-old Texel sheep were used to study the isotype-specific serum antibody responses against infective larvae and adult worms of Haemonchus contortus. Group Group 1 sheep (n = 7) were infected with 20,000 L3 larvae (Week 0), treated with ivermectin 6 weeks post-infection and subsequently challenged at Week 10 of the experiment. This challenge consisted of a trickle infection of 10,000 L3 larvae per week for 5 weeks. Group 2 sheep (n = 7) received a single infection at Week 10 of the experiment, and Group 3 (n = 5) served as a non-infected control group throughout the entire experiment. Individual blood and faeces samples were collected at weekly intervals. The immune responses were monitored by ELISA and Western blotting. The secondary immune response coincided with a significant reduction of the Haemonchus egg output and reduction of worm counts. Both primary and challenge infections induced humoral immune responses, and ELISA revealed that the most dominant serum antibody responses belong to the IgG1 isotype and to a lesser extent to IgG2. IgM and IgA responses were less dominant. Western blotting experiments demonstrated that many antigens were commonly recognized by antibodies from both primary and challenge infected animals. However, sera of immune animals specifically reacted with low molecular weight proteins. In particular, a 24 kDa antigen present in adult worms appeared to be specifically recognized.