The effect of Haemonchus contortus and Trichostrongylus colubriforms infection on the ruminal microbiome of lambs.

We evaluated Haemonchus contortus (HC) and Trichostrongylus colubriformis (TC) infection on the ruminal microbial community of Santa Ines lambs to better understand the pathophysiology of parasite infections and the interactions among gastrointestinal nematodes and gut resident microbiota. In this study, 18 six months of age lambs were maintained for 34 days in individual pens divided into three treatments that included animals infected with HC and TC, and control (infection-free). Haematological, ruminal parameter and microbial nitrogen absorbed by pune derivatives, as well as enteric methane emission (CH4), were analysed, and the rumen microbial taxonomic and functional profile assessed by shotgun metagenomics. The analysis showed that total protein, albumin, urea, and butyrate level were lower in animals infected by both parasites, while HC infection also decreased the haemoglobin level. Both infected groups (TC and HC) increased the enteric methane emission (CH4). TC and HC infections increased the diversity and richness of functional microbial genes. Most alterations in the rumen microbiome composition of infected groups are associated with the suppression of microbes involved in microbial homeostasis maintenance and expansion of the archaeal community in the infected animals. Infection led to an increased abundance of nitrogen, amino acid, protein, and energy metabolism genes. Overall, TC and HC infection increased the enteric methane emission, negatively affected taxon's responsible for maintenance de rumen homeostasis and modulated some important genes related to protein and energy metabolism.

Within-host mechanisms of immune regulation explain the contrasting dynamics of two helminth species in both single and dual infections.

Variation in the intensity and duration of infections is often driven by variation in the network and strength of host immune responses. While many of the immune mechanisms and components are known for parasitic helminths, how these relationships change from single to multiple infections and impact helminth dynamics remains largely unclear. Here, we used laboratory data from a rabbit-helminth system and developed a within-host model of infection to investigate different scenarios of immune regulation in rabbits infected with one or two helminth species. Model selection suggests that the immunological pathways activated against Trichostrongylus retortaeformis and Graphidium strigosum are similar. However, differences in the strength of these immune signals lead to the contrasting dynamics of infections, where the first parasite is rapidly cleared and the latter persists with high intensities. In addition to the reactions identified in single infections, rabbits with both helminths also activate new pathways that asymmetrically affect the dynamics of the two species. These new signals alter the intensities but not the general trend of the infections. The type of interactions described can be expected in many other host-helminth systems. Our immune framework is flexible enough to capture different mechanisms and their complexity, and provides essential insights to the understanding of multi-helminth infections.

A co-infection with two gastrointestinal nematodes alters host immune responses and only partially parasite dynamics.

Given their global distribution and abilities to persist in the host, helminths can play a crucial role in affecting risk of infections by increasing individual variation in infection. Helminth co-infections are of particular interest because by altering host immune responses, they can modify host susceptibility and thus intensity and transmission of other parasites/pathogens. The dynamics of co-infection were examined using two helminths of the European rabbit. Individuals were simultaneously challenged with a primary dose of both parasites, and changes in intensity were examined in relation to local and systemic immune responses. Both helminths persisted in co-infected rabbits; however, contrasting dynamics and immune responses were observed. Graphidium strigosum intensity was high throughout the co-infection, while Trichostrongylus retortaeformis intensity decreased but was not completely cleared. A Th2 response was observed against G. strigosum, while a mixed Th1/Th2 profile was found to T. retortaeformis. A comparison with our previous work on single infections showed that G. strigosum intensity was higher in co-infected than single infected hosts, while T. retortaeformis showed no significant changes. Differences were also observed in the cytokine profiles, blood cell concentrations and antibody trends. Overall, host variability during helminth co-infections can be generated by significant differences in immune responses and/or parasite dynamics.

Immuno-epidemiology of chronic bacterial and helminth co-infections: observations from the field and evidence from the laboratory.

Co-infections can alter the host immune responses and modify the intensity and dynamics of concurrent parasitic species. The extent of this effect depends on the properties of the system and the mechanisms of host-parasite and parasite-parasite interactions. We examined the immuno-epidemiology of a chronic co-infection to reveal the immune mediated relationships between two parasites colonising independent organs, and the within-host molecular processes influencing the dynamics of infection at the host population level. The respiratory bacterium, Bordetella bronchiseptica, and the gastrointestinal helminth, Graphidium strigosum, were studied in the European rabbit (Oryctolagus cuniculus), using long-term field data and a laboratory experiment. We found that 65% of the rabbit population was co-infected with the two parasites; prevalence and intensity of co-infection increased with rabbit age and exhibited a strong seasonal pattern with the lowest values recorded during host breeding (from April to July) and the highest in the winter months. Laboratory infections showed no significant immune-mediated effects of the helminth on bacterial intensity in the lower respiratory tract but a higher abundance was observed in the nasal cavity during the chronic phase of the infection, compared with single bacterial infections. In contrast, B. bronchiseptica enhanced helminth intensity and this was consistent throughout the 4-month trial. These patterns were associated with changes in the immune profiles between singly and co-infected individuals for both parasites. This study confirmed the general observation that co-infections alter the host immune responses but also highlighted the often ignored role of bacterial infection in helminth dynamics. Additionally, we showed that G. strigosum had contrasting effects on B. bronchiseptica colonising different parts of the respiratory tract. At the host population level our findings suggest that B. bronchiseptica facilitates G. strigosum infection, and re-infection with G. strigosum assists in maintaining bacterial infection in the upper respiratory tract and thus long-term persistence.

In silico exploration of the mechanisms that underlie parasite-induced anorexia in sheep.

A model was used to investigate two mechanisms describing reductions in food intake (anorexia) observed during gastrointestinal parasitism in lambs, and to explore relationships between anorexia and food composition. The mechanisms were either a reduction in intrinsic growth rate, leading to a consequent reduction in food intake (mechanism 1; M1), or a direct reduction in food intake (mechanism 2; M2). For both mechanisms, lambs growing from 2 to 6 months of age were modelled, with one of three levels of trickle challenge with Teladorsagia circumcincta. Scenarios were simulated for feeds varying in either protein or energy content, or both. Major differences were found between the predictions resulting from M1 and M2 on low-energy foods that constrained the intake of uninfected lambs through bulk. With M1, food intake was governed by the first operating constraint, whereas with M2 an additivity of constraints was observed. On the other foods, the duration of anorexia increased with increasing energy content of feed for M1, whilst the duration of anorexia decreased with increasing protein content of feed for M2.For foods that did not have an impact upon lambs' gastrointestinal tract capacity, published data were consistent with predictions of M2. Due to an absence of experimental data, no conclusions could be drawn for relationships between anorexia and food composition in the presence of other limiting constraints, such as bulk for low-energy foods. In conclusion, available experimental data and model predictions were consistent with anorexia having an impact directly on food intake, and with impacts of anorexia increasing with decreasing protein content.

Influence of gastrointestinal trichostrongylidosis on ram fertility.

A study on the influence of gastrointestinal trichostrongyles on ram fertility was performed. Two groups of semen donor rams (Sarda breed) were utilized; one was experimentally infected with Haemonchus contortus, Trichostrongylus colubriformis and Teladorsagia circumcincta and the other was used as a control group. In all animals, coprological, haematological and reproductive parameters were studied. The results suggest that the parasites had a limited effect with some changes in phosphorus, cholesterol and chlorine levels. In our experience the parasitic burden produced no significant change on ram fertility.

Effects of single or concurrent infections with Eimeria alabamensis and gastrointestinal nematodes on the performance of calves on pasture.

Twenty-four calves unexposed to pasture were allocated to four groups and inoculated with either two doses of 5 million Eimeria alabamensis oocysts at turn-out (E), 90,000 L3 of Ostertagia ostertagi and Cooperia oncophora divided on six occasions (N) or both oocysts and larvae as above (E + N). A control group was left uninoculated (C). For 10 weeks, the groups grazed in separate uniform paddocks not previously grazed by cattle. By day 5, most calves in groups E and E + N developed clinical coccidiosis that resulted in reduced weight gain compared to C and N. Mean trichostrongylid faecal egg counts in groups N and E + N never exceeded 300 eggs per gram of faeces, and average serum pepsinogen levels were less than 3.8 U tyrosine. This experiment demonstrates the potential impact of E. alabamensis on the performance of previously unexposed calves, whereas no aggravated effects were observed due to concurrent infections with gastrointestinal nematodes.

Nematode parasites and scrapie: experiments in sheep and mice.

To demonstrate the possible role of nematode parasites in the modification of host susceptibility to scrapie, experiments were conducted using sheep naturally exposed to scrapie, chosen by their genotype at the PrP gene, and infected with Teladorsagia circumcincta. Two 4-year duration experiments demonstrated that the nematode infection shortened the development of scrapie with a significant regression between the level of infection and age at first scrapie symptoms (P < 0.006). Investigations by ELISA tests in different species of nematode parasites of the digestive tract collected from scrapie infected ewes did not reveal the presence of PrPSc. In scrapie-infected C57BL mice, infected or not with Heligmosoides polygyrus at various times, parasitized animals showed a slight but significantly longer survival period. Assays on transmission by the larvae hatching from eggs collected from scrapie-infected mice were unsuccessful. We concluded that nematodes modify host susceptibility to scrapie, but their role in the horizontal transmission of the disease was not demonstrated.

Parasitic gastritis in a llama (Lama glama) associated with inhibited larval Teladorsagia spp. (Nematoda: Trichostrongyloidea).

A 7-year-old female llama was experimentally infected with 500 Fasciola hepatica metacercariae then turned out onto pasture also grazed by domestic sheep. The llama was necropsied approximately 22 weeks post infection. Routine examination of the gastrointestinal tract revealed diffusely coalescing, umbilicated nodules covering the caudal one-fifth of the third stomach compartment. Microscopically, the mucosa was irregularly thickened. Numerous nematode larvae were present in glandular lumens, often extending to the base of the glands. Where nematodes were most numerous, decreased numbers of parietal cells, attenuation of glandular epithelium and increased collagen within the lamina propria were evident. Of a total of 6510 adult nematodes in the third stomach compartment, 51% were Teladorsagia spp., 47% were Trichostrongylus axei, and 2% were Camelostrongylus mentulatus. Except for C. mentulatus, three sheep that had grazed with the llama and were necropsied at approximately the same time, harbored the same nematode species. The total number of larvae in the llama was 56,710, with more than 97% being ostertagiine early fourth-stage larvae. Ostertagiine larvae were also present in the sheep. Based on the composition of the adult populations in the llama and sheep, the larvae were considered to be species of Teladorsagia. Additionally, the larger numbers of early fourth-stage larvae indicated that the development of Teladorsagia spp. in the llama is inhibited.

Effect of subclinical coccidiosis in kids on subsequent trichostrongylid infection after weaning.

Seven-week-old female kids of the Murciana-Granadina breed naturally infected with coccidia were superinfected with a multispecific Eimeria inoculum (300,000 oocysts) or treated to control the coccidial infection with Amprolium (50 mg kg-1 liveweight day-1; 4 days every 14 days); 80 days later both animal groups received 2500 third-stage larvae of a sheep-derived mixture of Trichostrongylus colubriformis (50%), Teladorsagia circumcincta (40%) and Haemonchus contortus (10%). Kids experimentally superinfected with Eimeria showed reduced food intake at the early patency period, higher numbers of oocysts passed at weaning time and lower liveweight gain than the Amprolium-medicated kids. In the Eimeria superinfected kids the trichostrongyle infection caused a tendency to result in chronic coccidial infections. Further, these animals had higher numbers of nematode eggs in their faeces, lower dressed weights on slaughter and inferior meat quality.

Interaction of Ostertagia and Nematodirus species in sheep and the potential of serum fructosamine determination in monitoring gastrointestinal parasitism.

Serum fructosamine concentration falls with an increase in plasma protein turnover. Since this increase is a feature of gastrointestinal parasite infection at all sites, a falling serum fructosamine level may be of general application in the interpretation of parasite-related events. The circulating fructosamine level was investigated in the lamb as an indicator of protein-losing gastroenteropathy associated with two parasites at different sites, Ostertagia circumcincta (abomasum) and Nematodirus spathiger (small intestine). Infection with 10,000 N spathiger infective larvae daily for seven weeks produced only slight clinical signs, and only a small change in serum fructosamine levels. 2500 O circumcincta L3 daily gave no clinical signs in most animals, but serum fructosamine was more strongly affected in this group. Concurrent infection with both organisms caused some degree of diarrhoea in all lambs, and a sustained fall in serum fructosamine, more accentuated than that observed in either of the single infection groups, supporting the value of serum fructosamine determination in monitoring gastrointestinal parasitism.

Increased establishment of lungworms after exposure to a combined infection of Ostertagia ostertagi and Cooperia oncophora.

Three-month-old calves were infected three times weekly during a 5-week period with Cooperia oncophora, Ostertagia ostertagi or a combination of these two species. For each type of infection two dose levels were applied. In addition one group of calves was kept uninfected. After removal of the primary infection by anthelmintic treatment all calves were challenged with lungworm larvae and slaughtered 5 weeks later. The groups receiving either C. oncophora or O. ostertagi as a monospecific infection did not differ from the naïve controls. The group receiving the combination of both species differed significantly from the other groups, the establishment of the lungworms being 177%, and the faecal excretion of larvae being 325% of that of the other groups.

Pathophysiological and parasitological studies on a concurrent infection of Ostertagia ostertagi and Cooperia oncophora in calves.

Calves which had received daily concurrent infections of 2000 Ostertagia ostertagi and 10,000 Cooperia oncophora infective larvae over a 42-day period displayed a range of clinical signs typical of acute parasitic gastroenteritis including inappetence, weight loss, hypoalbuminaemia and diarrhoea. There were consistent and significant depressions in both digestive efficiency and nitrogen retention. Radioisotopic studies revealed marked disturbances in protein metabolism which were associated with high losses of plasma proteins into the gastrointestinal tract. On post mortem examination larval establishment of O ostertagi was seen to be high. The adverse changes were prevented by the prior administration of a morantel bolus.

Increased establishment of lungworms (Dictyocaulus viviparus) in calves after previous infections with gastrointestinal nematodes (Ostertagia ostertagi and Cooperia oncophora).

The influence of a priming infection with gastrointestinal nematodes on the subsequent establishment of lungworms was studied. Repeated inoculations of calves with Ostertagia ostertagi and Cooperia oncophora during 3, 5 or 7 weeks resulted in an establishment of lungworms that was 191% of the establishment found in naïve controls. The higher take was associated with a higher faecal output of lungworm larvae and with lower weight gains of calves. The effect was not significantly influenced by the duration of the primary infections or by the actual presence or absence of worms in the gastrointestinal tract.

Negative interactions between Ostertagia ostertagi and Cooperia oncophora in calves.

The interactions between Ostertagia ostertagi and Cooperia oncophora were studied in calves by concurrent and sequential infections. A reciprocal negative interaction between the 2 species was found in sequential, but not in concurrent infections. This result was supported by the finding of serological cross-reactions. It is suggested that the negative interaction is immunologically mediated. The depression of weight gain found after infection was similar for O. ostertagi- and C. oncophora-infected calves.

Impairment of primary expulsion of Trichuris muris in mice concurrently infected with Nematospiroides dubius.

Primary immune expulsion of Trichuris muris was markedly delayed by concurrent infection with Nematospiroides dubius. Maximum delay of expulsion was dependent on size and timing of N. dubius infection relative to T. muris infection. In NIH mice infection with 400 N. dubius larvae immediately before or after T. muris infection was found to be most effective in suppressing expulsion. Infection on day 8 of T. muris infection, when mice are sensitized to T. muris, also impaired expulsion. From this evidence it is suggested that the larvae of N. dubius are immunosuppressive and that the efferent role of the immune response to T. muris is inhibited. The results are discussed in terms of non-specific immunosuppression and their relevance to the tropical disease situation is emphasized.

Alkaline phosphatase activities in intestinal mucosa from calves infected with Cooperia punctata and Eimeria bovis.

Thirty calves 12 weeks of age raised under essentially parasite-free conditions were used to determine the effects of Cooperia punctata and Eimeria bovis (in single and combination infections) on mucosal alkaline phosphatase activities at 8 locations in the small intestine. In experiment 1, 5 calves infected with C punctata 3 weeks previously had highly significant (P less than 0.01) reductions in mucosal alkaline phosphatase activities compared with those in 5 noninfected control calves. These reductions were greatest in the 2 locations of the intestine closest to the pylorus. Infected calves had a mean of 44,356 C punctata adults present. In experiment 2, 5 calves infected with E bovis 2 weeks previously had significant (P less than 0.05) reductions in mucosal alkaline phosphatase activities compared with those in 5 noninfected control calves. These reductions were present in the caudal half of the intestine. Numerous 1st-generation E bovis schizonts were present in the caudal third of the intestine. In experiment 3, 5 calves infected with C punctata and E bovis of the same durations as in experiments 1 and 2 had highly significant (P less than 0.01) reductions in mucosal alkaline phosphatase activities in the cranial half of the intestine compared with those in the controls. These reductions were much larger than in either of the monospecific infections (experiments 1 and 2). A mean of 31,968 adult C punctata were recovered from the infected calves, and numerous E bovis schizonts were observed in the caudal third of the intestine.