Molecular and metabolomic changes in the proximal colon of pigs infected with Trichuris suis.

The pig whipworm Trichuris suis is important in swine production because of its negative effects on pig performance and, notably, to some humans with inflammatory bowel disease as a therapeutic agent that modulates inflammation. The proximal colon of T. suis-infected pigs exhibited general inflammation around day 21 after inoculation with infective eggs that is transcriptionally characterized by markers of type-2 immune activation, inflammation, cellular infiltration, tissue repair enzymes, pathways of oxidative stress, and altered intestinal barrier function. Prominent gene pathways involved the Th2-response, de novo cholesterol synthesis, fructose and glucose metabolism, basic amino acid metabolism, and bile acid transport. Upstream regulatory factor analysis implicated the bile acid/farnesoid X receptor in some of these processes. Metabolic analysis indicated changes in fatty acids, antioxidant capacity, biochemicals related to methylation, protein glycosylation, extracellular matrix structure, sugars, Krebs cycle intermediates, microbe-derived metabolites and altered metabolite transport. Close to 1,200 differentially expressed genes were modulated in the proximal colon of pigs with a persistent adult worm infection that was nearly 90% lower in pigs that had expelled worms. The results support a model to test diets that favorably alter the microbiome and improve host intestinal health in both pigs and humans exposed to Trichuris.

The whipworm (Trichuris suis) secretes prostaglandin E2 to suppress proinflammatory properties in human dendritic cells.

Clinical trials have shown that administration of the nematode Trichuris suis can be beneficial in treating various immune disorders. To provide insight into the mechanisms by which this worm suppresses inflammatory responses, an active component was purified from T. suis soluble products (TsSPs) that suppress---- TNF and IL-12 secretion from LPS-activated human dendritic cells (DCs). Analysis by liquid chromatography tandem mass spectrometry identified this compound as prostaglandin (PG)E2. The purified compound showed similar properties compared with TsSPs and commercial PGE2 in modulating LPS-induced expression of many cytokines and chemokines and in modulating Rab7B and P2RX7 expression in human DCs. Furthermore, the TsSP-induced reduction of TNF secretion from DCs is reversed by receptor antagonists for EP2 and EP4, indicating PGE2 action. T. suis secretes extremely high amounts of PGE2 (45-90 ng/mg protein) within their excretory/secretory products but few related lipid mediators as established by metabololipidomic analysis. Culture of T. suis with several cyclooxygenase (COX) inhibitors that inhibit mammalian prostaglandin synthesis affected the worm's motility but did not inhibit PGE2 secretion, suggesting that the worms can synthesize PGE2 via a COX-independent pathway. We conclude that T. suis secretes PGE2 to suppress proinflammatory responses in human DCs, thereby modulating the host's immune response.-Laan, L. C., Williams, A. R., Stavenhagen, K., Giera, M., Kooij, G., Vlasakov, I., Kalay, H., Kringel, H., Nejsum, P., Thamsborg, S. M., Wuhrer, M., Dijkstra, C. D., Cummings, R. D., van Die, I. The whipworm (Trichuris suis) secretes prostaglandin E2 to suppress proinflammatory properties in human dendritic cells.

Co-operative suppression of inflammatory responses in human dendritic cells by plant proanthocyanidins and products from the parasitic nematode Trichuris suis.

Interactions between dendritic cells (DCs) and environmental, dietary and pathogen antigens play a key role in immune homeostasis and regulation of inflammation. Dietary polyphenols such as proanthocyanidins (PAC) may reduce inflammation, and we therefore hypothesized that PAC may suppress lipopolysaccharide (LPS) -induced responses in human DCs and subsequent T helper type 1 (Th1) -type responses in naive T cells. Moreover, we proposed that, because DCs are likely to be exposed to multiple stimuli, the activity of PAC may synergise with other bioactive molecules that have anti-inflammatory activity, e.g. soluble products from the helminth parasite Trichuris suis (TsSP). We show that PAC are endocytosed by monocyte-derived DCs and selectively induce CD86 expression. Subsequently, PAC suppress the LPS-induced secretion of interleukin-6 (IL-6) and IL-12p70, while enhancing secretion of IL-10. Incubation of DCs with PAC did not affect lymphocyte proliferation; however, subsequent interferon-γ production was markedly suppressed, while IL-4 production was unaffected. The activity of PAC was confined to oligomers (degree of polymerization ≥ 4). Co-pulsing DCs with TsSP and PAC synergistically reduced secretion of tumour necrosis factor-α, IL-6 and IL-12p70 while increasing IL-10 secretion. Moreover, both TsSP and PAC alone induced Th2-associated OX40L expression in DCs, and together synergized to up-regulate OX40L. These data suggest that PAC induce an anti-inflammatory phenotype in human DCs that selectively down-regulates Th1 response in naive T cells, and that they also act cooperatively with TsSP. Our results indicate a novel interaction between dietary compounds and parasite products to influence immune function, and may suggest that combinations of PAC and TsSP can have therapeutic potential for inflammatory disorders.

Trichuris suis secrete products that reduce disease severity in a multiple sclerosis model.

Multiple sclerosis is a chronic inflammatory central nervous system (CNS) disease, which affects about 1 in 1000 individuals in the western world. It has been suggested that this relatively high prevalence is linked to a high level of hygiene, i.e. a reduced exposure to various microorganisms, including parasites. Parasites are known to employ different immunomodulatory and antiinflammatory strategies, which enable them to evade destruction by the immune system. We have investigated the immunomodulation by the swine whipworm, Trichuris suis, by measuring the impact of oral administration of T. suis ova as well as of intraperitoneal administration of T. suis excretory/secretory products on the development and progression of experimental autoimmune encephalomyelitis - an animal model that shares clinical and pathological characteristics with multiple sclerosis. Intraperitoneal administration of excretory/secretory products before disease onset, resulted in a significant decrease in disease severity as well as markedly reduced TH1 and TH17 T-cell responses, centrally in the spinal cord as well as in the periphery, i.e. the spleen. Thus, parenteral administration of T. suis-derived products results in a skewing of the immune response with a significant impact on disease severity in a CNS inflammatory disease model.

Profiling circulating miRNAs in serum from pigs infected with the porcine whipworm, Trichuris suis.

microRNAs (miRNAs) are recently discovered as key regulators of gene translation and are becoming increasingly recognized for their involvement in various diseases. This study investigates the miRNA profile in pig serum during the course of an infection with the gastrointestinal parasite, Trichuris suis. Of this panel, the expression of selected miRNAs in serum from T. suis infected and uninfected pigs were determined by quantitative real time PCR using Exiqon Human Panel assays at 0, 2, 4, 6, 8 and 10 weeks post first infection (wpi). One miRNA, ssc-let-7d-3p, was significantly up-regulated in infected pigs 8 wpi. Interestingly, ssc-let-7d-3p shows high complementary to tsu-let-7a, which is the most highly transcribed miRNA in T. suis. The let-7 family miRNAs have been shown to post-transcriptionally regulate the translation of the helminth-controlling cytokine, IL-13, in a murine model for asthma and we hypothesize possible interactions between these host- and parasite-derived miRNAs and their immunomodulating roles.

Temperature dependent embryonic development of Trichuris suis eggs in a medicinal raw material.

The therapeutic potential of infective pig whipworm eggs, Trichuris suis ova (TSO), is currently tested in several clinical trials on immune-mediated diseases. This paper studied the embryonic development of TSO in a medicinal raw product, where the parasite eggs were suspended in sulphuric acid (pH1). Unembryonated T. suis egg batches were stored at 5, 10, 15, 20, 25, 30, and 40°C (±1°C) and examined at 2, 4, 8, and 14 weeks. Subsequently, sub-batches from each temperature were allowed to embryonate for additional 14 weeks at 25°C, and selected samples were tested for infectivity in Göttingen minipigs. Both male and female pigs were used to evaluate eventual gender specific infectivity. Storage at 30°C up to 14 weeks and subsequent embryonation for 14 weeks at 25°C did not significantly reduce the overall larval establishment in minipigs, as compared to storage at 5°C and subsequent embryonation at 25°C. As marked impairment of egg development was observed during storage at 40°C, a second set of unembryonated egg batches were incubated at 30, 32, 34, 36, 38, and 40°C (±1°C) for 1-8 weeks. The development of the eggs was repeatedly examined by manual light microscopy, multispectral analysis (OvaSpec), and an egg hatching assay prior to the final testing in minipigs (Trial 1). These methods showed that the development started earlier at higher temperatures, but the long-term storage at higher temperature affected the egg development. The present study further documents tolerance of the TSO to storage at temperature 5-15°C, at which temperature development of larvae is not initiated.

Bacteria-induced egg hatching differs for Trichuris muris and Trichuris suis.

BACKGROUND: Eggs of the porcine whipworm Trichuris suis are currently explored in human clinical trials as a treatment of immune-mediated diseases. In this context, only the infective, embryonated eggs, constitute the Active Pharmaceutical Ingredient (API). The rodent whipworm, Trichuris muris is commonly used as a laboratory model to study Trichuris biology. The embryonated eggs (containing a fully developed larva) are biologically active and will invade the large intestinal mucosa of the host. This study aims to assess the in vitro hatching of T. muris and T. suis eggs in various bacterial cultures as a measure for their biological activity. METHODS: Eggs of T. muris and T. suis were incubated with Escherichia coli strain (BL-21) at three concentrations in a slightly modified in vitro egg hatching assay previously developed for T. muris. Additionally, E. coli strains (M15, SG13009, PMC103, JM109, TUNER, DH5alpha, TOP10) and five Gram-positive bacteria (Enterococcus caccae, Streptococcus hyointestinalis, Lactobacillus amylovorus, L. murinus, and L. reuteri) were tested as a hatching stimulus for T. muris and T. suis eggs. RESULTS: Whereas T. muris eggs hatched, T. suis did not, even when exposed to different concentrations and strains of E. coli after 4 and 24-hour incubation. When incubated with Gram-positive bacteria, only T. muris eggs showed noticeable hatching after 20 h, although with high variability. CONCLUSIONS: The observed difference in hatching of T. muris and T. suis eggs incubated with selected bacteria, indicate significant biological differences which may reflect specific adaptation to different host-specific gut microbiota.

Serum antibody responses in pigs trickle-infected with Ascaris and Trichuris: Heritabilities and associations with parasitological findings.

A humoral immune response following helminth infection in pigs is well documented. However, it has been difficult to confirm the existence of antibody mediated resistance against the large roundworm, Ascaris suum, and whipworm, Trichuris suis, in experimental settings by correlating worm burdens or egg excretion with specific antibody levels. We set out to investigate the association between worm load and T. suis and A. suum specific serum antibody levels (IgG1, IgG2 and IgA) against excretory-secretory products of adults and third stage larvae, respectively, measured at 0, 7 and 14 weeks p.i. in a trickle-infected F1-resource-population of crossbred pigs (n=195). Furthermore, we wanted to determine the heritability of these antibody isotypes during the course of infection. Most pigs remained infected with A. suum throughout the experiment while they expelled T. suis between 7 and 14 weeks post infection (p.i.). Parasite specific IgG1 and IgA were significantly (P<0.001) elevated after 7 and 14 weeks of infection, whereas parasite specific IgG2 levels only changed slightly at 14 weeks p.i.. However, the observed association between specific antibody isotype levels and faecal egg counts and macroscopic worm load was weak. The relative heritabilities of the different parasite specific isotypes were assessed and resulted in significant heritability estimates for parasite specific IgG1 and IgA. The highest heritabilities were found for A. suum specific IgG1 (h(2)=0.41 and 0.46 at 7 and 14 weeks p.i., respectively). Thus, the present study demonstrates that host genetic factors influence the IgG1 and IgA antibody isotype responses specific to two of the most common gastrointestinal nematodes of swine whereas specific antibody levels were poorly associated with egg excretion and the presence of macroscopic worms.

In vitro hatching of Trichuris suis eggs.

Eggs of the pig whipworm, Trichuris suis ova (TSO), are currently tested in human clinical trials for their potential immunomodulatory capacity. The biological potency of TSO (egg viability and infectivity) is traditionally assessed in Göttingen minipigs as the establishment of intestinal larvae after inoculation with a known number of eggs. To minimize testing in animal models, development of an in vitro egg hatching assay is proposed as a reliable, cost-effective, and a faster alternative to test the egg viability. The present study aimed to investigate the influence of different chemical, physical, and biological factors on egg hatching. Thus, in a series of experiments and in different combinations, the eggs were stimulated with glass beads, artificial gastric juice, bile salt and trypsin solution, fermentation gut medium, or stimulated with mucosal scrapings from the ileum and the large intestine of the infected and uninfected Göttingen minipig. Mechanical stimulation with glass beads presented a simple and reproducible method for egg hatching. However, incubation of eggs with mucosal scrapings from the ileum, caecum, and colon for 24 h at 38 °C significantly increased hatching.

Secretion of RNA-Containing Extracellular Vesicles by the Porcine Whipworm, Trichuris suis.

Trichuris suis is a common parasitic helminth of pigs. As with many other parasites, T. suis ensures its own survival by evading host immune responses, but little is known about how this is achieved. MicroRNAs (miRNA) have been shown to be involved in various immunological processes by post-transcriptional regulation of specific genes, and the potential of using these molecules as biomarkers of disease is currently being examined. It has recently been shown that parasites may secrete extracellular structures such as exosomes and microvesicles, containing proteins and miRNA. The fusion of these structures with host cells has been demonstrated, and a role of exosome-derived miRNA in host gene regulation has been suggested. In the present study, we show that exosome- and microvesicular-like structures are secreted by T. suis L1 larvae and also demonstrate the presence of miRNA-sized RNA inside these structures. A potential role of these molecules in host-parasite interactions is suggested. In addition, an electron-dense layer covering the surface of the larvae was observed, which may play a function in host immune evasion.

Dose-dependent establishment of Trichuris suis larvae in Göttingen minipigs.

Embryonated eggs of the pig whipworm Trichuris suis (TSOee) constitute the active pharmaceutical ingredient (API) in a medicinal product explored in human clinical trials against several immune-mediated diseases. The measurement of TSO biological potency (hatchability and infectivity) is a requirement for the assessment of TSO's pharmacological potency in human clinical trials. The present study aims to validate the dose-dependent establishment of T. suis larvae in Göttingen minipigs and eventual clinical implication of a dose range (1000-10,000 TSO). Four groups of 5 minipigs were inoculated with doses of 1000, 2500, 7500, and 10,000 TSOee, respectively, to evaluate a range of concentrations of TSOee in a minipig infectivity model. Unembryonated eggs (TSOue) were added to keep the total egg number in the inoculum constant at 10,000 eggs. Two groups received 2500 and 7500 TSOee per pig without the addition of TSOue as controls. The intestinal larval establishment at 21 days post inoculation (dpi) demonstrated a clear positive linear dose-response relationship between numbers of inoculated TSOee and recovered larvae. There was a low level of variation in larval counts in all study groups. Thus, the infectivity model in minipigs within the tested dose range offers a reliable, sensitive and accurate assay for testing biological potency of TSO.

Immune and inflammatory responses in pigs infected with Trichuris suis and Oesophagostomum dentatum.

The aim of the present study was to investigate parasite induced immune responses in pigs co-infected with Trichuris suis and Oesophagostomum dentatum as compared to mono-species infected pigs. T. suis is known to elicit a strong immune response leading to rapid expulsion, and a strong antagonistic effect on O. dentatum populations has been observed in co-infected pigs. Forty-eight helminth naïve pigs were allocated into 4 groups in a 2-factorial design. Two groups were trickle inoculated with either 10 T. suis eggs/kg/day (Group T) or 20 O. dentatum L3/kg/day (Group O). Group OT was infected with same levels of both T. suis and O. dentatum (Group OT) and Group C remained uninfected. In each group, six pigs were necropsied after 35 days and the remaining pigs after 71 days. Parasite E/S-antigen specific serum antibodies were quantified by an in-direct ELISA. qPCR was used to measure the expression of immune function related genes in the mucosa of proximal colon and the draining lymph node. Highly significant interactions were identified for O. dentatum specific IgG1 (p<0.0001) and IgG2 (p<0.0006) antibodies with a remarkable 2-fold higher antibody response in group OT pigs as compared to group O. These findings indicated that T. suis enhanced the antibody response against O. dentatum in Group OT. The gene expression data confirmed a strong Type 2 response to T. suis (e.g. marked increase in IL-13, ARG1 and CCL11) and clearly weaker in amplitude and/or delayed onset response to O. dentatum in the single infected group. Interactions were found between the two nematodes with regard to several cytokines, e.g. the increase in IL-13 observed in Group T was absent in Group OT (p=0.06, proximal colon mucosa, 35 and 71 p.i.). Some of these immune response-related interactions may support, or even partially explain, the observed interactions between the two worm populations in co-infected pigs.

Parasite population dynamics in pigs infected with Trichuris suis and Oesophagostomum dentatum.

The aim of the present study was to investigate the population dynamics and potential interactions between Trichuris suis and Oesophagostomum dentatum in experimentally co-infected pigs, by quantification of parasite parameters such as egg excretion, worm recovery and worm location. Forty-eight helminth naïve pigs were allocated into four groups. Group O was inoculated with 20 O. dentatum L3/kg/day and Group T with 10 T. suis eggs/kg/day. Group OT was inoculated with both 20 O. dentatum L3/kg/day and 10 T. suis eggs/kg/day, while Group C was kept as an uninfected control group. All inoculations were trickle infections administered twice weekly and were continued until slaughter. Faecal samples were collected from the rectum of all pigs at day 0, and twice weekly from 2 to 9 weeks post first infection (wpi). Six pigs from each group were necropsied 5 wpi and the remaining 6 pigs from each group were necropsied 10 wpi. The faecal egg counts (FEC) and total worm burdens of O. dentatum were dramatically influenced by the presence of T. suis, with significantly lower mean FECs and worm burdens at 5 and 10 wpi compared to single infected pigs. Furthermore, in the presence of T. suis we found that O. dentatum was located more posteriorly in the gut. The changes in the Trichuris population were less prominent, but faecal egg counts, worm counts 5 wpi (57% recovered vs. 39%) and the proportion of infected animals at 10 wpi were higher in Group OT compared to Group T. The location of T. suis was unaffected by the presence of O. dentatum. These results indicate an antagonistic interaction between T. suis and O. dentatum which is dominated by T. suis.

Trichuris suis-induced modulation of human dendritic cell function is glycan-mediated.

Human monocyte-derived dendritic cells (DCs) show remarkable phenotypic changes upon direct contact with soluble products (SPs) of Trichuris suis, a pig whipworm that is experimentally used in therapies to ameliorate inflammation in patients with Crohn's disease and multiple sclerosis. These changes may contribute to the observed induction of a T helper 2 (Th2) response and the suppression of Toll-like receptor (TLR)-induced Th1 and Th17 responses by human DCs primed with T. suis SPs. Here it is demonstrated that glycans of T. suis SPs contribute significantly to the suppression of the lipopolysaccharide (LPS)-induced expression in DCs of a broad variety of cytokines and chemokines, including important pro-inflammatory mediators such as TNF-α, IL-6, IL-12, lymphotoxin α (LTA), C-C Motif Ligand (CCL)2, C-X-C Motif Ligands (CXCL)9 and CXCL10. In addition, the data show that human DCs strongly bind T. suis SP-glycans via the C-type lectin receptors (CLRs) mannose receptor (MR) and DC-specific ICAM-3-grabbing non-integrin (DC-SIGN). The interaction of DCs with T. suis glycans likely involves mannose-type glycans, rather than fucosylated glycans, which differs from DC binding to soluble egg antigens of the human worm parasite, Schistosoma mansoni. In addition, macrophage galactose-type lectin (MGL) recognises T. suis SPs, which may contribute to the interaction with immature DCs or other MGL-expressing immune cells such as macrophages. The interaction of T. suis glycans with CLRs of human DCs may be essential for the ability of T. suis to suppress a pro-inflammatory phenotype of human DCs. The finding that the T. suis-induced modulation of human DC function is glycan-mediated is novel and indicates that helminth glycans contribute to the dampening of inflammation in a wide range of human inflammatory diseases.

Soluble helminth products suppress clinical signs in murine experimental autoimmune encephalomyelitis and differentially modulate human dendritic cell activation.

The increased incidence of auto-inflammatory and autoimmune diseases in the developed countries seems to be caused by an imbalance of the immune system due to the lack of proper regulation. Helminth parasites are well known modulators of the immune system and as such are of great interest for the treatment of these disorders. Clinical studies showed that administration of eggs of the pig nematode Trichuris suis to patients with inflammatory bowel disease reduces the disease severity. Here we demonstrate that treatment with soluble products from the nematodes T. suis and Trichinella spiralis induces significant suppression of symptoms in murine experimental autoimmune encephalomyelitis, a validated animal model for multiple sclerosis. These data show that infection with live nematodes is not a prerequisite for suppression of inflammation. To translate these results to the human system, the effects of soluble products of T. suis, T. spiralis and Schistosoma mansoni on the phenotype and function of human dendritic cells (DCs) were compared. Our data show that soluble products of T. suis, S. mansoni and T. spiralis suppress TNF-α and IL-12 secretion by TLR-activated human DCs, and that T. suis and S. mansoni, but not T. spiralis, strongly enhance expression of OX40L. Furthermore, helminth-primed human DCs differentially suppress the development of Th1 and/or Th17 cells. In conclusion, our data demonstrate that soluble helminth products have strong immunomodulatory capacities, but might exert their effects through different mechanisms. The suppressed secretion of pro-inflammatory cytokines together with an upregulation of OX40L expression on human DCs might contribute to achieve this modulation.

Population dynamics of Ascaris suum in trickle-infected pigs.

The population dynamics of Ascaris suum was studied by long-term exposure of pigs to infective eggs. The pigs were experimentally inoculated with 25 A. suum eggs/kg/day, and 7, 8, and 8 pigs were necropsied at weeks 4, 8, and 14 postinoculation (PI), respectively. Despite the fact that the pigs were continuously reinfected, dramatic reductions in numbers of liver lesions (white spots) and migrating lung larvae were observed as a function of time. However, even at the end of the study, a few larvae were able to complete migration, but these larvae seemed unable to mature in the small intestine. Thus, the adult worm population seemed to consist of worms from the first part of the exposure period. The noticeable decrease in number of white spots suggests that the level of exposure is not reflected in the number of white spots in the late phase of a continuous infection. The serum levels of A. suum L3-specific IgG1 and IgA were significantly elevated by week 4 PI, after which the antibody levels declined. The population dynamics and parasite regulating mechanisms are discussed for A. suum in pigs as well as for the closely related species A. lumbricoides in humans.

A time course study of immunological responses in Trichuris suis infected pigs demonstrates induction of a local type 2 response associated with worm burden.

In order to investigate immunological changes over time in pigs infected with Trichuris suis, we inoculated 40 pigs with 5000 infective T. suis eggs and left 40 pigs as uninfected controls. Equal numbers of pigs from both groups were sacrificed every other week from 1 to 11 weeks p.i. At necropsy tissue samples were collected from all pigs and their worm burdens were determined. In the proximal colon of T. suis-infected pigs infiltration of eosinophils peaked 5 weeks p.i. and mast cell infiltration developed from 5 to 11 weeks p.i. Histological evaluation of the proximal colon revealed that the presence of T. suis was closely associated with intestinal histopathological changes such as crypt hyperplasia, goblet cell hyperplasia and a general hypertrophy of mucosa. The crypt lengths were positively associated with worm burdens. Real-time PCR analysis of genes related to immune function indicate a local increased transcription of genes coding for CCR3, ARG1, MUC5AC, IL-4, IL-5, IL-13, FcepsilonR1alpha, and IL-13Ralpha2 and decreased expression of genes coding for iNOS, TNF-alpha, IL-10, CD3epsilon, CD80, CD86, IL-4Ralpha, IL-13Ralpha1 and CD40 in the proximal colon of pigs infected with T. suis. This local T-helper cell Type 2-like gene-expression pattern indicates that the Type 2 immune response characteristic of helminth infections in both mouse and humans also develops in pigs infected with T. suis. The results from this study expand our knowledge of the immunomodulatory effect of T. suis, a parasite that has proven effective in treating inflammatory bowel disease, when its eggs are administered regularly to patients.

Trichuris suis population dynamics following a primary experimental infection.

Trichuris suis population kinetics was studied by experimentally infecting 40 pigs with 5000 T. suis infective eggs. Six pigs were sacrificed every 2 weeks from 1 to 9 weeks post-inoculation (p.i.) and the remaining 10 pigs were sacrificed 11 weeks p.i. to estimate worm burdens. An equal number of uninfected control pigs were sacrificed at the same time points for comparison. Egg excretions from each pig were evaluated every week from 5 to 11 weeks p.i. Peripheral blood eosinophilia and basophilia were also evaluated every 2 weeks throughout the experimental period. After an initial almost 100% establishment of T. suis an expulsion phase followed approximately 9 weeks p.i., resulting in an aggregated distribution of the worms in the pig population, as it is characteristic for most helminth infections. By 11 weeks p.i. almost all worms had been expelled. Egg excretion peaked 7 weeks p.i. and a significant non-linear relationship between worm burdens and egg excretion was found. The predilection site for T. suis was the caecum and proximal colon and the relative distribution of worms in the large intestine did not change over time until expulsion. Peaking peripheral blood eosinophil and basophil levels were observed in the T. suis infected pigs 5 and 7 weeks p.i., respectively, reflecting the host activated immune response against the parasite. We here describe the course of a primary T. suis infection in pigs by detailed worm counts, demonstrating an effective expulsion that results in an almost 100% clearance of infection as previously indicated by monitoring faecal egg excretion.