Onset and duration of fecal shedding, cell-mediated and humoral immune responses in pigs after challenge with a pathogenic isolate or attenuated vaccine strain of Lawsonia intracellularis

Lawsonia intracellularis regulates nuclear factor-κB signalling pathway during infection

Lawsonia intracellularis is the etiological agent of proliferative enteropathy (PE) in pigs, horses and wide range of mammals. Little is known about the role of innate immune response during L. intracellularis infection. In this study, we investigated the nuclear factor-κB (NF-κB)-regulated immune response against infection of a clinical strain Dkp23 and a live-attenuated Enterisol vaccine strain in PK-15 cells. We found that expression of NF-κB target genes TNF-α, IFN-γ, IL-6 and IL-8 were modulated during the course of infection. At 5 dpi, there was a significant increase in p65 NF-κB activation, including protein nuclear translocation and phosphorylation, synchronous with the induction of IL-6, IFN-γ and IL-8 expression in L. intracellularis infected cells, especially for Enterisol vaccine strain-infected cells. This result suggests that NF-κB signalling level is induced when L. intracellularis bacterial load peaks at 5 dpi. The induction of pro-inflammatory cytokines expression is consistent with the decreased viability of L. intracellularis-infected cells especially that of the vaccine strain. There were no significant changes in NF-κB signalling between vaccine and Dkp23 infection in PK-15 cells, except for moderate levels of differences in NF-κB target genes expression which might be a reflection of differences in intracellular bacterial load. Overall, the data presented here indicate a correlation between the induction of NF-κB signalling and the L. intracellularis bacterial load in PK-15 cells.

Epidemiology Tools to Evaluate the Control of Proliferative Enteropathy in Commercial Pig Herds

Proliferative enteropathy (PE) is characterized by diarrhea and reduced weight gains in growing pigs and intestinal hemorrhage in finishers. Vaccination, antibiotic medication, and improved hygiene can control PE, but their efficacy depends upon the epidemiology of PE. This study monitored the timing and severity of PE in 84 commercial pens across seven treatments, including disinfection, vaccination, no treatment, medication with olaquindox (50, 25 and 12.5 ppm), and combined disinfection and vaccination. Vaccination with or without lime disinfection suppressed clinical signs of PE and reduced the number of excreted L. intracellularis relative to untreated pigs housed in cleaned or cleaned and disinfected pens between 9 and 17 weeks of age. Continuous olaquindox mediation to 17 weeks of age prevented L. intracellularis infection, leaving finisher pigs naïve. These finisher pigs suffered an outbreak of hemorrhagic enteropathy with significant reductions in weight gain, feed intake, and mortalities of 4.6%. Over the 13 week grow/finish period, vaccinated pigs housed in disinfected pens showed significantly higher weight gain and feed intake relative to all other treatments, equating to a weight gain difference of between 3.6 and 3.9 kg per pig. Monitoring the immune response and fecal excretion of L. intracellularis in pens of pigs enabled effective PE control strategies to be evaluated on the farm.

Salmonella vector induces protective immunity against Lawsonia and Salmonella in murine model using prokaryotic expression system

BACKGROUND

Lawsonia intracellularis is the causative agent of proliferative enteropathy and is associated with several outbreaks, causing substantial economic loss to the porcine industry.

OBJECTIVES

In this study, we focused on demonstrating the protective effect in the mouse model through the immunological bases of two vaccine strains against porcine proliferative enteritis.

METHODS

We used live-attenuated Salmonella Typhimurium (ST) secreting two selected immunogenic LI antigens (Lawsonia autotransporter A epitopes and flagellin [FliC]-peptidoglycan-associated lipoprotein-FliC) as the vaccine carrier. The constructs were cloned into a Salmonella expression vector (pJHL65) and transformed into the ST strain (JOL912). The expression of immunogenic proteins within Salmonella was evaluated via immunoblotting.

RESULTS

Immunizing BALB/c mice orally and subcutaneously induced high levels of LI-specific systemic immunoglobulin G and mucosal secretory immunoglobulin A. In immunized mice, there was significant upregulation of interferon-γ and interleukin-4 cytokine mRNA and an increase in the subpopulations of cluster of differentiation (CD) 4+ and CD 8+ T lymphocytes upon splenocytes re-stimulation with LI antigens. We observed significant protection in C57BL/6 mice against challenge with 106.9 times the median tissue culture infectious dose of LI or 2 × 109 colony-forming units of the virulent ST strain. Immunizing mice with either individual vaccine strains or co-mixture inhibited bacterial proliferation, with a marked reduction in the percentage of mice shedding Lawsonia in their feces.

CONCLUSIONS

Salmonella-mediated LI gene delivery induces robust humoral and cellular immune reactions, leading to significant protection against LI and salmonellosis.

Alleviative Effect of Probiotic Ferment on Lawsonia intracellularis Infection in Piglets

(1) Background: Lawsonia intracellularis (LI) is an obligate intracellular Gram-negative bacterium that causes porcine ileitis. Pigs infected with LI have severe ileal lesions and show symptoms of diarrhea, indigestion, and growth retardation. Previous studies found that probiotic ferment (FAM) improved the growth performance, gut barrier, and function in piglets. Therefore, we aimed to reveal the mechanism that FAM alleviates negative performance in LI-challenged piglets by characterizing the changes in intestinal integrity, function, and gut microbiota following FAM supplementation. (2) Methods: Twenty-four healthy piglets were randomly allotted to four treatments. Three groups were challenged with LI; both FAM addition and vaccination were performed to explore their positive effects on LI-infected piglets. (3) Results: Piglets infected with LI showed lower growth performance and typical pathological symptoms. Moreover, microscopic images showed that observed intestinal morphological damage could be repaired by FAM and vaccine. To explore the digestion of nutrients in piglets, both digestive enzyme activity and ileal transporter expression were performed to reveal the promoting effect of additives. Reduction of LI colonization intervention by FAM could also ameliorate abnormal differentiation and function of intestinal epithelial cells and alleviate severe inflammatory responses in piglets. Regarding the gut microbiota, both the structure and function of the ileal and colonic microbiota were altered following FAM supplementation. (4) Conclusions: In conclusion, probiotic ferment can reduce the colonization of LI in the ileum, improve intestinal damage, barrier function and microbiota structure, and enhance digestive enzyme activity and nutrient transport proteins expression, thereby improving piglet growth performance, which has the effect of preventing ileitis in pigs.

Development and validation of a flow cytometry antibody test for Lawsonia intracellularis

Lawsonia intracellularis is the etiologic agent of porcine proliferative enteropathy (PPE), an inflammatory bowel disease with a major economic impact on the pig industry. The serological diagnosis of PPE can be performed using Blocking or Indirect ELISA, Immunoperoxidase Monolayer Assay (IPMA) and Indirect Fluorescence Antibody Test (IFAT). Here, we designed a most sophisticated immunological method for the detection of porcine anti-L. intracellularis IgGs, named Flow Cytometry Antibody Test - FCAT. This assay uses whole, live-attenuated L. intracellularis bacteria derived from a commercial vaccine. For the assay, we set up the optimal antigen concentration (10⁶ bacterium/assay), primary antibody dilution (1:100), time of incubation (20 min), antigen stability (15 days), precision (coefficient of variation - CV < 10%), reproducibility (CV ≤ 13%) and Receiver Operating Characteristic (ROC). When using a cut-off of >15.15% for FCAT, we determined that it showed a sensitivity of 98.8% and specificity of 100%. The rate of agreement with IPMA was 84.09% with a kappa index of 0.66. FCAT was used to screen 1,000 sera from non-vaccinated pigs housed in 22 different farms and we found that 730 pigs (73%) from 16 farms (72.7%) had L. intracellularis IgG. This high prevalence confirms that L. intracellularis is endemic on Brazilian pig farms. Finally, we determined that FCAT is an easy to perform diagnostic assay and we would highly recommend it for: i) seroepidemiological studies; ii) evaluation of infection dynamics; and iii) characterization of the humoral response profile induced by vaccines.

Experimental infection of high health pigs with porcine circovirus type 2 (PCV2) and Lawsonia intracellularis

Background

Porcine circovirus type 2 (PCV2) and Lawsonia intracellularis infections can cause enteritis in pigs. A Danish study showed a significantly higher probability of detecting PCV2 without concurrent L. intracellularis infection, indicating that one of these pathogens has an impact on the dynamics of the other. Therefore, a delayed co-infection model was set up, initially aiming at investigating the interaction between PCV2 and L. intracellularis in pigs challenged with PCV2 and 2 weeks later with L. intracellularis. But due to PCV2 contamination of the L. intracellularis inoculum the aim was revisited to describing the infection dynamics and pathogenesis of pigs infected with PCV2 followed by delayed simultaneous exposure to PCV2 and L. intracellularis. Twenty-four high-health piglets were divided into three groups of eight pigs (A, B, C) and inoculated at experimental day (EXD) 0 with mock (groups A and B) or PCV2 (group C), and at EXD 14 with mock (group A) or L. intracellularis/PCV2 (groups B and C). The pigs underwent daily clinical examination, and were necropsied at EXD 51–52. Furthermore, histology, immunohistochemistry, serology and PCR for PCV2 and L. intracellularis, and measurement of C-reactive protein were carried out.

Results

Group A remained negative for PCV2 and L. intracellularis. Following inoculation with L. intracellularis/PCV2, no significant differences were observed between group B and C, however pigs already infected with PCV2 (group C) showed milder clinical signs and exhibited milder intestinal lesions, less shedding of L. intracellularis and developed higher L. intracellularis antibody titers than the pigs in group B that only received the combined infection. Though the differences between group B and C were non-significant, all results pointed in the same direction, indicating that the pigs in group B were more affected by the L. intracellularis infection compared to the pigs in group C.

Conclusions

Previous exposure to PCV2 had limited impact on the subsequent exposure to a combined L. intracellularis/PCV2 inoculation. However, there was a tendency that the infection dynamics of PCV2 and development of antibodies to PCV2 and L. intracellularis were altered in pigs previously exposed to PCV2. These differences should be confirmed in further experimental trials.

The Effectiveness of Commercial Vaccination against Lawsonia intracellularis in Mitigating the Reduction in ADWG, the Increased Mortality and Fecal Shedding of the Vaccinated Pigs: A Systematic Review and Meta-Analysis

In this study, a systematic review and meta-analysis was conducted to assess the efficacy of commercial vaccines against PPE in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist. Of the 373 articles reviewed, 16 fulfilled the pre-specified inclusion criteria. Three independent reviewers extracted the data, and vaccine effectiveness was assessed using the outcomes of interest. The majority of studies had a low or unclear risk of bias as assessed using the ARRIVE guidelines. The results of the meta-analysis indicated that the vaccination resulted in statistically significant reductions in bacterial fecal shedding (odds ratio, OR = 0.122, 95% confidence interval, CI 0.054−0.278) and mortality rate (risk ratio, RR = 0.199; 95% CI, 0.066−0.605). Furthermore, ADWG was significantly increased in the vaccinated pigs compared to the unvaccinated controls (standardized mean difference (SMD) = 0.606, 95% CI 0.243−0.969). In the subgroup analysis, the production phase and study type significantly influenced the effect size (p < 0.1). The Egger’s regression test showed no evidence of publication bias (p > 0.1). The effectiveness of commercially available vaccines against PPE-related weight loss, fecal shedding, and mortality suggests that the vaccines may help control PPE on affected swine farms.

Serological Assessment of Ascaris suum Exposure in Greek Pig Farms and Associated Risk Factors Including Lawsonia intracellularis

The effects of nematodes and bacteria on intestinal health are of primary importance in modern swine production. The aim of the present study was to assess the seropositivity status of Ascaris suum infection in fatteners in intensive swine farms in Greece and address possible risk factors, including Lawsonia intracellularis as a predisposing factor to swine ascariosis. In total, 360 blood serum samples from pigs in the late fattening period, from 24 Greek swine farrow-to-finish farms (15 samples/farm) were collected and tested with Svanovir® A. suum antibody ELISA and Ileitis antibody ELISA. The results demonstrated 34.4% seropositive samples for A. suum and 42.2% for L. intracellularis. The analysis of predisposing risk factors suggested that the frequency of application of anthelminthic treatment to sows more than two times per year was significantly associated with the lower likelihood of A. suum infection, whereas a greater likelihood of A. suum infection was observed in pigs with concurrent L. intracellularis exposure. The results highlight the importance of proper anthelminthic metaphylaxis of the breeding stock, as well as the likely outcome of concurrent exposure to two intestinal pathogens in pigs, implying a possible association between intestinal nematodes and bacteria in swine.

PREVALENCE OF LAWSONIA INTRACELLULARIS INFECTION IN NONHUMAN PRIMATES AND PEST RODENTS IN A ZOOLOGICAL COLLECTION

In 2016 and 2017, Lawsonia intracellularis was isolated from several pileated gibbons (Hylobates pileatus) presenting with diarrhea in Mulhouse Zoo (eastern France). To this day, infection with this bacterium has rarely been described in nonhuman primates (NHP) in captivity or in the wild and there are no data about the prevalence or transmission of the disease. This study focuses on finding the prevalence of this infection amongst Mulhouse Zoo's NHP collection and trying to identify a source of contamination responsible for this epizooty. Forty-eight real-time PCR were conducted on feces from all NHP species in the zoo and on small mammals trapped in the NHP housing structures. No NHP was experiencing symptoms at the time of the study, however test results showed that Lawsonia intracellularis can be found in 61.76% (21/34) of the group total (n = 34) and the prevalence even increases to 92.3% (12/13) in the Lemuriform infraorder (n = 13). In small mammals (n = 14), prevalence of the bacterium is 57.17% (8/14) including 77.78% in rodents (7/9). The results of this study show that several NHP species are healthy carriers and some species of small mammals can be considered as a potential source of contamination. Because of the difficulty encountered trying to isolate the bacterium, it is plausible that infections caused by Lawsonia intracellularis have been underdiagnosed to this day, and that it could be an emerging disease in Europe. Therefore, using real-time PCR to search for this bacterium seems essential in case of diarrhea occurring in nonhuman primates. Moreover, even though further studies on contamination sources need to be conducted, the issue of the presence of rodents in NHP housing structures has to be taken very seriously and tackled with the utmost care.

Evaluation of immunogenicity and protection mediated by Lawsonia intracellularis subunit vaccines

Lawsonia intracellularis is an economically important bacterium that causes ileitis in pigs. Current vaccines for L. intracellularis do not allow for differentiation between infected and vaccinated animals (DIVA), which is beneficial for disease tracking and surveillance. Previously, we identified five putative surface L. intracellularis proteins that were targeted by antibodies from pigs infected with L. intracellularis which could serve as antigens in a subunit vaccine. We conducted two trials to determine whether these antigens were immunogenic and provided protection against infectious challenge and whether truncated glycoprotein D could be used as a DIVA antigen. For Trial 1, 5 week-old piglets were administered intramuscular monovalent vaccines comprised of a recombinant (r) flagella subunit protein (rFliC,) and DIVA antigen (truncated glycoprotein D (TgD), a herpes virus antigen) both formulated with a combination adjuvant consisting of polyinosinic:polycytidylic acid(poly I:C), host defense peptide 1002 and polyphosphazene, referred to as Triple Adjuvant (TriAdj). Relative to control animals, animals vaccinated with rFliC and rTgD had significantly elevated antigen-specific humoral immunity in sera suggesting that rFliC and TgD are immunogenic. Control animals had negligible anti-TgD titres suggesting that TgD may be a suitable DIVA antigen for pigs. For Trial 2, piglets were immunized with a trivalent vaccine (FOG vaccine consisting of rFLiC, rOppA protein (a ABC Type dipeptide transport system) and rGroEL (a stress response protein)) and a divalent vaccine (CM vaccine consisting of rClpP (an ATP-dependent Clp protease proteolytic subunit) and rMetK (a S-adenosyl methionine synthase)) formulated with Emulsigen®. Relative to the control pigs, pigs immunized with the FOG vaccine produced robust and significantly higher serum IgG antibodies against rFliC and rGroEL, and significantly higher anti-FliC and anti-GroEL IgA antibodies in jejunal (GroEL only) and ileal intestinal mucosa. Pigs immunized with CM vaccine produced significantly higher serum antibodies against rClpP and rMetK and significantly higher anti-rClpP IgA antibodies in the ileum relative to the control pigs. Quantitative polymerase chain reaction (qPCR) analysis showed that 18 days after challenge with infectious L. intracellularis, challenged/control pigs and pigs that received the CM vaccine, but not the pigs vaccinated with the FOG vaccine, shed significantly more bacteria in feces than the unchallenged controls pigs. These data suggest that the FOG vaccinated pigs showed limited protection. While promising, more work is needed to enhance the efficiency of the intramuscular vaccine to show significant disease protection.

Review of methods for the detection of Lawsonia intracellularis infection in pigs

Lawsonia intracellularis is an obligate intracellular bacterium associated with enteric disease in pigs. Clinical signs include weight loss, diarrhea, and, in some cases, sudden death. The hallmark lesion is the thickening of the intestinal mucosa caused by increased epithelial cell replication, known as proliferative enteropathy. The immune response to L. intracellularis is not well defined, and detection of the infection, especially in the early stages, is still a significant challenge. We review here the main approaches used to identify this important but poorly understood pathogen. Detection of L. intracellularis infection as the cause of clinical disease is confounded by the high prevalence of the pathogen in many countries and that several other pathogens can produce similar clinical signs. A single L. intracellularis–specific ELISA and several amplification assays are available commercially to aid detection and surveillance, although histopathology remains the primary way to reach a conclusive diagnosis. There are major gaps in our understanding of L. intracellularis pathogenesis, especially how the host responds to infection and the factors that drive infection toward different clinical outcomes. Knowledge of pathogenesis will increase the predictive value of antemortem tests to guide appropriate interventions, including identification and treatment of subclinically affected pigs in the early stages of disease, given that this important manifestation reduces pig productivity and contributes to the economic burden of L. intracellularis worldwide.

Probiotics mediated gut microbiota diversity shifts are associated with reduction in histopathology and shedding of Lawsonia intracellularis

BACKGROUND

Clinical intervention during bacterial infections in farm animals such as pigs commonly includes the use of antimicrobials. With the rise of antimicrobial resistance and the attempts to reduce the use of antibiotics in food animals, effective alternatives are urgently needed to reduce or even remove pathogens and disease risks. Improving clinical outcomes and overall pig health by using probiotics appears attractive. However, reliable data sets on the efficacy of probiotics are scarce. The obligate intracellular bacterium Lawsonia intracellularis is widespread in pigs and associated with severe enteropathy, mainly in the ileum, commonly resulting in substantial reduction in weight gain. The impact of three in-feed probiotics and a commercial live L. intracellularis vaccine was compared in a pig challenge model. Probiotic treatment was associated with reduced L. intracellularis fecal shedding and reduced gut lesions. Here, the bacterial microbiota of the ileum of these pigs was characterized with 16S rRNA gene sequencing and was subsequently analyzed with bioinformatics tools.

RESULTS

The greatest microbial richness was observed in the probiotic treated group T03-LAW, which accounted for 87% of richness observed in the study. Treatment had a significant impact on both the microbiota structure and taxonomic profile in the ileum, explaining between 26 and 36% of the structural variation, with the strongest association in the T03-LAW group. Overall, the largest changes were observed for the pigs treated with in-feed Bacillus pumilus; the microbiota of these pigs had the greatest diversity and highest richness. We also observed depleted and enriched core microbiota amongst the groups; however, there was no correlation with clinical characteristics. The results suggest that an increased diversity of the ileal microbiota is associated with a reduction in shedding, i.e. a unit increase in Shannon diversity index resulted in 2.8 log reduction in shedding.

CONCLUSIONS

Probiotic supplementation of a base feed ration increased ileum microbiota diversity leading to a mitigation of the effects of a pathogenic L. intracellularis challenge. An even and diverse microbiota community benefits pigs infected with L. intracellularis, however, investigations are needed to determine if this is also true for other pathogens. The study unambiguously demonstrates the usefulness of probiotic supplementation in reducing the impact of enteric pathogens and pathogen shedding rates in food animals without the use of antimicrobials.

Correlation of Lawsonia intracellularis positivity in quantitative PCR and herd factors in European pig herds

BACKGROUND

Lawsonia intracellularis is causing diarrhea, poor growth and sudden death in pigs. It can be found in most pig populations leading to large economic losses worldwide. Many potential risk factors for the occurrence of disease or seropositivity have been described. The current study therefore focused on herd characteristics in European countries associated with direct detection of the pathogen determined by quantitative polymerase chain reaction.

RESULTS

A median number of less than 30 nursery pigs per pen was correlated to less positive nursery pigs (p < 0.01) and generally less samples positive per herd (p < 0.05) as well as a lower median of genome equivalents determined per herd (p < 0.05). Routine use of zinc oxide at/ around weaning, which was mentioned by 41.0% of all farmers, was correlated to higher number of positive nursery pigs (p < 0.01) as well as higher median genome equivalents determined per herd (p < 0.05). Slatted flooring of more than 78.0% of the surface in nursery units was correlated to lower number of positive animals (p < 0.05) and a lower median of genome equivalents per herd (p < 0.05). A weight of more than 7.8 kg at weaning was correlated to a higher number of positive growing pigs (p < 0.05) as well as general higher number of positive samples/ herd (p < 0.01).

CONCLUSIONS

Weaning and subsequent accommodation of nursery pigs seem to be of particular importance in prevention of infection with Lawsonia intracellularis and the spread of the pathogen within the herd.

Survival of Lawsonia intracellularis in porcine peripheral blood monocyte-derived macrophages

Lawsonia intracellularis, an obligately intracellular enteric bacterium, infects intestinal epithelial cells, but may also be found within macrophages in the intestinal lamina propria of affected pigs. Macrophages play an important role in host defense against infectious agents, but the role of this cell in L. intracellularis infection is not well understood. The aim of this study was to evaluate the permissibility of macrophages to L. intracellularis infection in vitro. Pure culture of L. intracellularis was added to swine peripheral blood monocyte-derived macrophages. Viability of intracytoplasmic L. intracellularis was evaluated at different time points by transmission electron microscopy (TEM). Potential replication of L. intracellularis in macrophages was also evaluated by qPCR. By TEM, phagocytosis L. intracellularis within of phagolysosomes were observed 1-hour post-infection (hpi) and bacterial structures in binary fission at 48 hpi. The number of intracellular bacteria was determined at 1, 4, 24, 48, and 72 hpi by qPCR in infected macrophages and compared to the number of intracellular bacteria from culture in McCoy cells. In both cell lines, the amount of L. intracellularis was decreased at 4 hpiand increased at 24 hpi. The number of intracellular bacteria continued to increase in McCoy cells over time. This is the first study showing interaction, survival and propagation of L. intracellularis in macrophages. These findings are critical to establish an experimental model for future studies of the pathogenesis of porcine proliferative enteropathy and the potential persistence of L. intracellularis in macrophages during chronic infections.

Impact of dietary vitamin D3 supplements in nursery diets on subsequent growth and bone responses of pigs during an immune challenge

Limited evidence is available to validate beneficial responses from extra nutrient supplements for mediation of growth suppression that results from immune challenges. Extrarenal roles of vitamin D metabolites in immune function implicate vitamin D3 supplements as a nutrient for potential beneficial effects. The current objective was to assess growth and bone ash responses to dietary vitamin D3 (D) supplements for growing pigs undergoing an immune challenge. At weaning, 216 crossbred pigs (4 pigs/pen, 6 pens/treatment) were randomly allotted within sex and weight blocks to 1 of the 9 treatments. Treatments included D supplements (0, 100, or 800 IU/kg) in a factorial arrangement with 3 vaccine (V) protocols; no injection (0 × V), a single 2 mL injection of a Lawsonia intracellularis vaccine at day 14 (1 × V), or 2 mL injections of the same vaccine at days 0 and 7 (2 × V). An adjustment diet with no supplemental D was fed for 1 wk, then assigned D diets for 2 wk (P2). After P2, all pigs were phase-fed standard diets (D = 280 IU/kg) to assess subsequent growth to 115 kg. No differences due to D supplements or vaccination protocol were detected in ADG (0.233 ± 0.021 kg/d) or GF (0.642 ± 0.028 kg/d) over the 21-d nursery trial; however, ADFI was lower (P < 0.10) in pigs fed D levels of 0 vs. 100 and 800 (0.340 vs. 0.375, 0.372 ± 0.027 kg/d). Bone mineral content (g) from whole-body dual energy X-ray absorptiometry scans at 9 wk (n = 4 pigs/treatment) was lower in pigs fed 0 vs. 100 and 800 IU of D (287 vs. 325, 323 ± 34.1 g/pig). Growth from nursery to 115 kg was lower (P < 0.01) in pigs fed D levels of 0 vs.100 and 800 (0.828 vs. 0.876, 0.889 ± 0.021 kg/d). At market, approximately two-thirds of pigs showed positive L. intracellularis serology titers regardless of treatment. Limited evidence for D-mediation of an immune challenge using the vaccination protocols may be a consequence of limited vaccine effects on growth in the nursery and seroconversion of most pigs to L. intracellularis by market.

Prevalence of Lawsonia intracellularis in pig herds in different European countries

Background

Lawsonia intracellularis causes large economic losses in the pig industry worldwide. Pigs suffer from reduced daily weight gain, poor feed conversion ratio and increased mortality. The number of affected animals and herds in Europe remains unknown. This study will provide an overview of the prevalence of Lawsonia intracellularis in herds with a history of diarrhoea in different European countries and thereby identify country specific differences.

Results

Out of the 144 herds sampled in Germany, Denmark, Spain, the Netherlands and the United Kingdom, 90.3% (79.2-100.0%) contained at least one positive faecal sample on quantitative polymerase chain reaction (qPCR). Of the 6450 nursery, growing and finishing pigs of the previously mentioned herds, 26.2% (15.9-41.5%) of the animals were tested positive in faecal samples. Enzyme linked immunosorbent assay (ELISA) results of 60 herds were 91.7% (70-100%) positive. The percentage of positive samples in these 1791 blood samples was 31.6% (20.3-51.0%). Herd prevalence did not differ significantly by qPCR or ELISA. Significant differences between the countries were found regarding: Within-herd prevalence- qPCR: Samples from Denmark were more often positive than samples of Spain or the United Kingdom. Within-herd prevalence- ELISA: Samples from Denmark were more often positive than samples from Spain and the Netherlands. Affected age category- qPCR: Nursery pigs in Denmark were more often positive and shed more genome equivalents than nursery pigs in the other countries. Concentration of detected genome equivalents- qPCR: The concentration of genome equivalents from Lawsonia intracellularis in herds in Denmark was higher compared to all other countries.

Conclusion

A widespread of Lawsonia intracellularis in the six European countries was confirmed, whereby a large part of the positive animals only excreted small amounts of genome equivalents. Country specific differences were found with Denmark in particular diagnosing more Lawsonia intracellularis then the other countries. Herd data collected in this study needs to be analysed to get more information about possible reasons for the differences found between the countries.

Immune response and protection against Lawsonia intracellularis infections in pigs

Lawsonia intracellularis are Gram-negative, obligate intracellular bacteria that cause proliferative enteropathy (PE), an economically important disease for the pig industry. Numerous reviews have been published on the characteristics and pathogenesis of this bacterium since its isolation and taxonomic characterization, with most reviews only partially covering how the host immune response develops during infection and the immune correlates of protection. With the development of increasingly more sophisticated immunological assays and tools for the pig, the immune response against L. intracellularis at distinct stages of pathogenesis has been published. In this review, we discuss current knowledge of the pig immune response against L. intracellularis and strategies to achieve immune protection. The immune response is presented in relation to chronological progression of pathological lesions and clinical symptoms, with emphasis on innate immunity and the adaptive humoral and cell-mediated immune response. The aim is to achieve a comprehensive understanding of the host immune response with respect to the stage-dependent cellular and biochemical processes important during PE development. Also, strategies for development of immune protection and new vaccination technologies are discussed in the light of new discoveries in the field.

Bacillus pumilus probiotic feed supplementation mitigates Lawsonia intracellularis shedding and lesions

The causative agent of ileitis, Lawsonia intracellularis, is commonly associated with diarrhea and reduced weight gain in growing pigs. The effect of in-feed probiotics on L. intracellularis infection dynamics was evaluated. In brief, 70 2.5-week-old-pigs were randomly divided into six groups with 10–20 pigs each. All pigs were fed an age appropriate base ration for the duration of the study, which was supplemented with one of three Bacillus strains including B. amyloliquefaciens (T01), B. licheniformis (T02) and B. pumilus (T03). Another group was orally vaccinated with a commercial live L. intracellularis vaccine (VAC) at 3 weeks of age. At 7 weeks of age, T01-LAW, T02-LAW, T03-LAW, VAC-LAW and the POS-CONTROL groups were challenged with L. intracellularis while the NEG-CONTROL pigs were not challenged. All pigs were necropsied 16 days later. By the time of inoculation, all VAC-LAW pigs had seroconverted and at necropsy 10–65% of the pigs in all other challenged groups were also seropositive. The results indicate a successful L. intracellularis challenge with highest bacterial DNA levels in POS-CONTROL pigs, VAC-LAW pigs and T01-LAW pigs. There was a delay in onset of shedding in T02-LAW and T03-LAW groups, which was reflected in less severe macroscopic and microscopic lesions, reduced intralesional L. intracellularis antigen levels and a lower area under the curve for bacterial shedding. Under the study conditions, two of the probiotics tested suppressed L. intracellularis infection. The obtained findings show the potential of probiotics in achieving antibiotic-free control of L. intracellularis.

Isolation and in vitro antimicrobial susceptibility of porcine Lawsonia intracellularis from Brazil and Thailand

BACKGROUND

Lawsonia intracellularis is an obligate intracellular bacterium which cannot be cultured by conventional bacteriological methods. Furthermore, L. intracellularis needs enriched medium and a unique atmosphere for isolation, cultivation and propagation. Because of this,there are only a few isolates of L. intracellularis available and few studies in vitro demonstrating the susceptibility of this bacterium to antimicrobial agents. The objectives of this study were to isolate South American and Southeast Asia strains of L.intracellularis and to determine the in vitro antimicrobial activity against these isolates. Tested antimicrobials included: chlortetracycline, lincomycin, tiamulin, tylosin and valnemulin(against both Brazilian and Thailand strains) and additionally, amoxicillin, zinc-bacitracin, carbadox, enrofloxacin, gentamicin, sulfamethazine, trimethoprim, spectinomycin and a combination (1:1) of spectinomycin and lincomycin were also tested against the Thai isolates. The minimum inhibitory concentration (MIC) was determined by the antimicrobial activity that inhibited 99% of L. intracellularis growth in a cell culture as compared to the control (antimicrobial-free).

RESULTS

Two strains from Brazil and three strains from Thailand were successfully isolated and established in cell culture. Each antimicrobial was evaluated for intracellular and extracellular activity. Pleuromutilin group (valnemulin and tiamulin) and carbadox were the most active against L. intracellularis strains tested. Tylosin showed intermediate activity, chlortetracycline had variable results between low and intermediate activity, as well as spectinomycin, spectinomycin and lincomycin, amoxicillin, sulfamethazine and enrofloxacin. L. intracellularis was resistant to lincomycin, gentamicin, trimethoprim, colistin and bacitracin in in vitro conditions.

CONCLUSIONS

This is the first report of isolation of L. intracellularis strains from South America and Southeast Asia and characterization of the antimicrobial susceptibility patterns of these new strains.

Spread of an Experimental Salmonella Derby Infection in Antibiotic-Treated or Lawsonia intracellularis Vaccinated Piglets

Lawsonia intracellularis infections are a common reason for antibiotic treatment in pig production. Experimental studies in animals naturally infected with Lawsonia intracellularis comparing the course of an experimental Salmonella infection in piglets previously treated with tylosin or vaccinated against Lawsonia intracellularis are scarce. A total of 72 seven-week-old Salmonella-free pigs were taken from a herd with a Lawsonia intracellularis history in piglet rearing. The pigs were divided into two groups with three replicates each. Animals had either been previously treated with tylosin (10 mg/kg body weight) for seven days (AB⁺VAC^-) or had been vaccinated as suckling pigs by drenching (Enterisol^®Ileitis; AB^-VAC⁺). Two animals per replicate were primarily infected with Salmonella Derby (1.04 × 10⁸ colony-forming units per animal). The detection of Salmonella in faeces (p < 0.0001, odds ratio: 3.8364) and in the ileocaecal lymph nodes (p = 0.0295, odds ratio: 3.5043) was significantly more frequent in AB⁺VAC^- animals. Overall, the odds ratio for detecting Salmonella in any substrate or organ was significantly higher in the AB⁺VAC^- group animals (p = 0.0004, odds ratio: 5.9091). Treatment with tylosin can significantly increase the spread of a Salmonella infection, which is not observed after early Lawsonia intracellularis vaccination.

Lawsonia intracellularis: Revisiting the Disease Ecology and Control of This Fastidious Pathogen in Pigs

Lawsonia intracellularis is an anaerobic obligate intracellular bacterium infecting the small intestine and infrequently also the large intestine of pigs and other animals including hamsters and horses. The infection is characterized by proliferation, hemorrhage, necrosis, or any combination commonly referred to as "ileitis," affecting the health and production efficacy of farmed pigs. Despite decades of research on this pathogen, the pathogenesis and virulence factors of this organism are not clearly known. In pigs, prophylaxis against L. intracellularis infection is achieved by either administration of subtherapeutic levels of in-feed antibiotic growth promoters or vaccination. While the former approach is considered to be effective in L. intracellularis control, potential regulations on subtherapeutic antibiotics in many countries in the near future may necessitate alternative approaches. The potential of manipulating the gut microbiome of pigs with feed ingredients or supplements to control L. intracellularis disease burden is promising based on the current understanding of the porcine gut microbiome in general, as well as preliminary insights into the disease ecology of L. intracellularis infection accrued over the last 30 years.

Effect of a live attenuated vaccine against Lawsonia intracellularis in weaned and finishing pig settings in Finland

Background

The intracellular bacterium Lawsonia intracellularis is an important pathogen in modern swine production. The aim of this study was to investigate the effect of a live attenuated L. intracellularis vaccine (Enterisol Ileitis^®) on the health and production parameters of weaned and finishing pigs in a commercial Finnish 850-sow farm with diagnosed L. intracellularis infection. The herd was free from enzootic pneumonia, swine dysentery, progressive atrophic rhinitis, sarcoptic mange and salmonellosis. Four weekly groups of approximately 500 piglets were included in the study for a total of approximately 2000 piglets. Half of these piglets were vaccinated at 3 weeks of age and the other half served as controls. The study piglets were ear-tagged with individual numbers and colour-coded and were individually weighed at weaning (4 weeks), delivery to the finishing farm (12–14 weeks) and at slaughter. Mortality, symptoms of diseases and medications of the study piglets were registered in the nursery and finishing unit. Feed conversion rate was calculated for the finishing period and lean meat percentage was measured at slaughter.

Results

Vaccinated piglets had a higher live weight than unvaccinated piglets at delivery to the finishing unit (+ 1.18 kg, P = 0.002) and at slaughter (+ 3.57 kg, P < 0.001). The daily weight gain of vaccinated piglets was better than unvaccinated piglets in the nursery (+ 14.8 g/d, P = 0.013) and in the finishing unit (+ 30.9 g/d, P < 0.001). Vaccination had no effect on feed conversion rate or lean meat percentage (P = 0.102). Altogether, 3.9 and 4.6% of the pigs were medicated for different reasons in the vaccinated and control groups, respectively. The return on investment for the vaccination was calculated to be 0.41.

Conclusions

Immunisation of piglets with a live attenuated L. intracellularis vaccine resulted in higher meat yield in pig production via significantly higher live weight and average daily weight gain in a Finnish specific pathogen-free setting.

Roles of dietary supplementation with arginine or N-carbamylglutamate in modulating the inflammation, antioxidant property, and mRNA expression of antioxidant-relative signaling molecules in the spleen of rats under oxidative stress

This study evaluated the effects of arginine (Arg) or N-carbamylglutamate (NCG) on inflammation, antioxidant property, and antioxidant-related gene expression in rat spleen under oxidative stress. A total of 52 rats were randomly distributed into 4 treatment groups with 13 replicates per group. Rats were fed a basal diet (BD) or BD supplemented with Arg or NCG for 30 days. On day 28, half of the BD-fed rats were intraperitoneally injected with sterile saline (control group), and the other half with 12 mg/kg body weight of diquat (DT; DT group). The other 2 diet groups were intraperitoneally injected with 12 mg/kg body weight of DT with either Arg (1%) (DT + Arg) or NCG (0.1%) (DT + NCG). Rat spleen samples were collected for analysis at 48 h after DT injection. Results showed that DT damaged the antioxidant defense in rats compared with the control group (P < 0.05). Compared with the DT group, the DT + Arg and DT + NCG groups manifested improved anti-hydroxyl radical, catalase, and total superoxide dismutase (T-SOD) activities, increased glutathione content (P < 0.05), and decreased malondialdehyde content (P < 0.05). Moreover, compared with the DT group, the DT + Arg and DT + NCG groups enhanced mRNA expression of superoxide dismutase (SOD), glutathione peroxidase 1 (GPx1), glutathione reductase (GR), nuclear factor erythroid 2-related factor 2 (Nrf2), Kelch-like ECH-associated protein 1(Keap-1), and mammalian target of rapamycin (mTOR) (P < 0.05). Both NCG and Arg significantly increased anti-inflammatory cytokine mRNA level but suppressed the pro-inflammatory cytokine mRNA expression under oxidative stress (P < 0.05). In summary, NCG and Arg effectively alleviated oxidative stress, improved the antioxidant capacity and regulated the antioxidant-related signaling molecular expression in rat spleen. N-carbamylglutamate and Arg reduced the inflammation in the spleen by mediating the gene expression of anti-inflammatory and pro-inflammatory cytokines and transforming growth factor-β (TGF-β).

Vaccination Against Lawsonia intracellularis Decreases Shedding of Salmonella enterica serovar Typhimurium in Co-Infected Pigs and Alters the Gut Microbiome

Salmonella enterica serovar Typhimurium continues to be a major cause of foodborne illness worldwide and pork can serve as a source of infection. Co-infection of S. enterica with Lawsonia intracellularis, a common intestinal pathogen of swine, has been found as risk factor for increased S. enterica shedding. The objective of this study was to investigate if vaccination against L. intracellularis could lead to decreased S. Typhimurium shedding. To test this hypothesis, pigs were challenged with either S. Typhimurium or S. Typhimurium and L. intracellularis, with and without L. intracellularis vaccination (n = 9 per group). A non-challenged group served as a negative control. Vaccination decreased the shedding of S. Typhimurium in co-infected animals by 2.12 log10 organisms per gram of feces at 7 days post infection. Analysis of the microbiome showed that vaccination led to changes in the abundance of Clostridium species, including Clostridium butyricum, in addition to other compositional changes that may explain the protection mediated against S. Typhimurium. These results indicate that vaccination against L. intracellularis in co-infected herds may provide a new tool to increase food safety by helping to prevent S. enterica without the need for antibiotics.

New insights into the role of dietary spermine on inflammation, immune function and related-signalling molecules in the thymus and spleen of piglets

This study aimed to determine the effects of dietary spermine supplementation on the inflammatory response and immune function of the thymus and spleen in piglets. Eighty suckling piglets were randomly assigned to receive adequate nutrients supplemented with spermine (0.4 mmol/kg body weight) or restricted nutrient intake supplemented with normal saline for 7 h or 3, 6 and 9 days in pairs. Regardless of treatment time, spermine supplementation decreased (p < 0.05, compared with the controls) the following: (1) tumour necrosis factor α (TNF-α), interleukin (IL)-1β, 2 and 6, and interferon (IFN)-γ levels in serum; (2) gene expression of cluster of differentiation 8 and integrin beta-2 in the thymus and spleen and the lymphocyte function-associated antigen 1 in the thymus; (3) mRNA levels of TNF-α, IL 1β, 2, 6, and 12, IFN-γ and inducible nitric oxide synthase in the thymus and spleen, as well as IL-8 in the spleen; and (4) eukaryotic IF4E-binding protein 1, Janus kinase 2, signal transducer and activator of transcription 3, and nuclear factor-kappa B P65 gene transcriptions in the thymus and spleen. By contrast, spermine supplementation increased (p < 0.05) the following: (1) immunoglobulin M, IL-10, and transforming growth factor β1 gene expression, as well as (2) relative mRNA levels of mammalian target of rapamycin (mTOR) and ribosomal protein S6 kinase 1 in the thymus and spleen. These effects were also observed upon prolonged spermine administration (p < 0.05). In summary, dietary spermine supplementation can alleviate inflammatory response, enhance the immune function and regulate the gene expression of signalling molecules related to inflammation.

Systemic cytokine response in pigs infected orally with a Lawsonia intracellularis isolate of South Korean origin

In the swine industry, Lawsonia intracellularis is one of the main enteric pathogens; it causes acute intestinal hemorrhage (proliferative hemorrhagic enteropathy) in naïve adult pigs and a wasting disease (proliferative enteropathy) in growing pigs. Among many kinds of cytokines, interferon-γ (IFN-γ) has previously been reported to play a significant role in limiting intracellular infection and increasing cellular proliferation associated with L. intracellularis. However, the levels of various circulating inflammatory cytokines, including IFN-γ, in animals infected with L. intracellularis is still an area of considerable interest for understanding immunity against this bacterium. In addition, there has been no information on cytokine response in animals infected with any L. intracellularis isolate of South Korean origin or Asian origin. To determine the relationship between the changes in the systemic inflammatory cytokine response in the peripheral blood of the host after L. intracellularis infection, we measured the levels of some pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IFN-γ), anti-inflammatory cytokines (IL-4, IL-10, and transforming growth factor-β (TGF-β)), and a chemokine (IL-8) in pigs infected with L. intracellularis isolated from South Korea. This study demonstrated that a L. intracellularis isolate of South Korean origin induced cytokine (TNF-α, IL-6, and IFN-γ) responses in infected animals within 15 days post-infection although the circulating levels of IL-4, IL-10, IL-8 and TGF-β were induced relatively late.

Identification of Lawsonia intracellularis putative hemolysin protein A and characterization of its immunoreactivity

Despite the recent global increase in fatal endemic outbreaks of proliferative enteropathy (PE) caused by the obligate intracellular bacterium Lawsonia intracelluralis (LI) in the swine industry, development of effective prevention strategies or immunodiagnostic tests has been delayed due to the difficulty of cultivating this pathogen in vitro. Although several genetic analyses have been performed at the level of gene transcription after the complete genome sequence of LI was made available, the mechanism of LI infection and virulence genes remain unidentified. In the present study, we assessed the antigenic features of the LI0004 protein, which we putatively defined as Lawsonia hemolysin A (LhlyA), by employing bioinformatics tools and in vivo and in vitro protein-based molecular assays. The amino acid sequence of LhlyA showed approximately 60% homology to the hemolysin-like proteins of Bilophila wadsworthia and Desulfovibrio piger. Presence of computationally predicted linear antigenic B-cell epitopes on the LhlyA protein was demonstrated by immunoblotting; a band with a molecular mass corresponding to the predicted size of the protein was strongly recognized by sera collected from artificially infected mice. Further, in an in vivo cytotoxicity assay, no splenomegaly was observed in mice inoculated with purified LhlyA. Collectively, the data presented here suggest that the LhlyA protein is a highly immuno-reactive antigen of L. intracellullaris and can potentially be used to develop effective protection strategies against PE.

Lawsonia intracellularis in Pigs: Progression of Lesions and Involvement of Apoptosis

The purpose of this study was to follow the progression of gross and histologic lesions and apoptosis events in Lawsonia intracellularis-infected enterocytes through the course of the disease, proliferative enteropathy (PE). Thirty 5-week-old pigs were divided into 2 groups: 20 challenged and 10 control animals. Groups of 3 pigs, 2 challenged and 1 control, were euthanized at 1, 3, 5, 8, 11, 15, 19, 24, 29, and 35 days after inoculation. Complete necropsies were performed with gross evaluation. Tissue samples from different sites of the gastrointestinal tract and other visceral organs were collected for routine histologic staining and for immunohistochemistry (IHC) for L. intracellularis. In addition, caspase-3, terminal deoxyuridine nick-end labeling assay, and electron microscopy were performed in ileum samples. Macroscopic and histologic lesions suggestive of PE were first detected 11 days after infection and continued through day 24. L. intracellularis antigen was first detected in the intestine by IHC on day 5 after inoculation, and the bacterium was first detected by transmission electron microscopy on day 15. Positive IHC staining for [L. intracellularis] and enterocyte proliferation, but no gross lesion, were detected on day 29. All 3 pigs euthanized on day 35 were grossly and histologically normal and IHC negative. Hyperplastic crypts in challenge pigs had more apoptotic cells on days 15, 19, and 24 postinfection ( P < .05) compared to control pigs. Our results demonstrated the progression of lesions and infection by L. intracellularis and that inhibition of enterocyte apoptosis is not involved in the pathogenesis of proliferative enteropathy.

Antibiotic Resistance in the Food Chain: A Developing Country-Perspective

Antibiotics are now "endangered species" facing extinction due to the worldwide emergence of antibiotic resistance (ABR). Food animals are considered as key reservoirs of antibiotic-resistant bacteria with the use of antibiotics in the food production industry having contributed to the actual global challenge of ABR. There are no geographic boundaries to impede the worldwide spread of ABR. If preventive and containment measures are not applied locally, nationally and regionally, the limited interventions in one country, continent and for instance, in the developing world, could compromise the efficacy and endanger ABR containment policies implemented in other parts of the world, the best-managed high-resource countries included. Multifaceted, comprehensive, and integrated measures complying with the One Health approach are imperative to ensure food safety and security, effectively combat infectious diseases, curb the emergence and spread of ABR, and preserve the efficacy of antibiotics for future generations. Countries should follow the World Health Organization, World Organization for Animal Health, and the Food and Agriculture Organization of the United Nations recommendations to implement national action plans encompassing human, (food) animal, and environmental sectors to improve policies, interventions and activities that address the prevention and containment of ABR from farm-to-fork. This review covers (i) the origin of antibiotic resistance, (ii) pathways by which bacteria spread to humans from farm-to-fork, (iii) differences in levels of antibiotic resistance between developed and developing countries, and (iv) prevention and containment measures of antibiotic resistance in the food chain.

Use of flow cytometry and PCR analysis to detect 5-carboxyfluoroscein-stained obligate intracellular bacteria Lawsonia intracellularis invasion of McCoy cells

In this study, we describe a method to quantify invasion of obligate intracellular bacteria, Lawsonia intracellularis, inside McCoy cells. In immunological research, the cell-permeable fluorescent dye 5'-carboxyfluoroscein succidyl ester (CFSE) is commonly used to quantify eukaryotic cellular proliferation. Instead of using it in this traditional way, we stained L. intracellularis with CFSE dye prior to infection of McCoy cells. Flow cytometry was performed to quantify the percentage of eukaryotic cells which had taken up or were associated with fluorescent bacteria. As obligate intracellular bacteria, they cannot replicate outside of eukaryotic cells and thus qPCR analysis was used to quantify bacterial growth. Indirectly, PCR analysis confirmed invasion rather than adherence to the McCoy cell surface. Fluorescent activated cell sorting (FACS) was used to sort the CFSE(+) (i.e. infected) McCoy cells from the CFSE(-) (i.e. non-infected) McCoy cells and confocal microscopy was used to confirm bacterial invasion and cytosolic localization of CFSE-L. intracellularis. To show that this approach could be used in conjunction with functional assays, we investigated the effect that serum antibodies had on CFSE-bacterial invasion and growth. Instead of blocking invasion, rabbit hyperimmune serum augmented invasion of the bacteria inside McCoy cells and qPCR analysis confirmed bacterial growth over the course of 5days. We conclude that CFSE-labeling of bacteria and qPCR can be used to track and quantify bacterial invasion and may be a valuable tool for studying the invasive properties of bacteria, especially if commercial antibodies are not available. This approach may be adapted for use in other obligate intracellular bacteria and intracellular pathogens.

Recent Advances in Understanding the Pathogenesis of Lawsonia intracellularis Infections

Proliferative enteropathy is an infectious disease caused by an obligate intracellular bacterium, Lawsonia intracellularis, and characterized by thickening of the intestinal epithelium due to enterocyte proliferation. The disease is endemic in swine herds and has been occasionally reported in various other species. Furthermore, outbreaks among foals began to be reported on breeding farms worldwide within the past 5 years. Cell proliferation is directly associated with bacterial infection and replication in the intestinal epithelium. As a result, mild to severe diarrhea is the major clinical sign described in infected animals. The dynamics of L. intracellularis infection in vitro and in vivo have been well characterized, but little is known about the genetic basis for the pathogenesis or ecology of this organism. The present review focuses on the recent advances regarding the pathogenesis and host-pathogen interaction of L. intracellularis infections.

The critical threshold of Lawsonia intracellularis in pig faeces that causes reduced average daily weight gains in experimentally challenged pigs

Serology indicates that Lawsonia intracellularis infection is widespread in many countries, with most pigs seroconverting before 22 weeks of age. However, the majority of animals appear to be sub-clinically affected, demonstrated by the low reported prevalence of diarrhoea. Production losses caused by sub-clinical proliferative enteropathy (PE) are more difficult to diagnose, indicating the need for a quantitative L. intracellularis assay that correlates well with disease severity. In previous studies, increasing numbers of L. intracellularis in pig faeces, quantified with a real time polymerase chain reaction (qPCR), showed a strong negative correlation with average daily gain (ADG). In this study, the association between faecal L. intracellularis numbers and PE severity was examined in two L. intracellularis experimental challenge trials (n1=32 and n2=95). The number of L. intracellularis shed in individual faeces was determined by qPCR on days 0, 7, 14, 17 and 21 days post challenge, and average daily gain was recorded over the same period. The severity of histopathological lesions of PE was scored at 21 days post challenge. L. intracellularis numbers correlated well with histopathology severity and faecal consistency scores (r=0.72 and 0.68, respectively), and negatively with ADG (r=-0.44). Large reductions in ADG (131 g/day) occurred when the number of L. intracellularis shed by experimentally challenged pigs increased from 10(7) to 10(8)L. intracellularis, although smaller ADG reductions were also observed (15 g/day) when the number of L. intracellularis increased from 10(6) to 10(7)L. intracellularis.

Comparison of a commercial ELISA with an indirect fluorescent antibody test to detect antibodies to Lawsonia intracellularis in experimentally challenged pigs

OBJECTIVE

The ability of a new commercial ELISA to detect pigs with subclinical proliferative enteropathy (PE) was compared with the traditional indirect fluorescent antibody test (IFAT).

METHODS

Serum samples were selected from pigs with known Lawsonia intracellularis infection status and clinical signs of PE, but the sample population consisted predominantly of pigs subclinically affected by PE.

RESULTS

Significant association and agreement were shown between the ELISA and IFAT assays. ELISA results correlated well with the duration of L. intracellularis shedding as detected by polymerase chain reaction.

CONCLUSION

ELISA can be successfully used to monitor L. intracellularis infection in pigs.

Lawsonia intracellularis infection and proliferative enteropathy in foals

Equine proliferative enteropathy (EPE) is a disease of foals caused by the obligate intracellular organism Lawsonia intracellularis. This organism is unique in that it causes proliferation of infected enterocytes, resulting in thickening of the intestinal epithelium, most often the small intestine. This disease affects mainly weanling foals and causes fever, lethargy, peripheral edema, diarrhea, colic and weight loss. The diagnosis of EPE may be challenging and relies on the presence of hypoproteinemia, thickening of segments of the small intestinal wall observed on abdominal ultrasonography, positive serology and molecular detection of L. intracellularis in feces. The epidemiology and genetic basis for pathogenesis for this disease is beginning to be elucidated. Phenotypic traits, genomic features, and gene expression profiles during L. intracellularis infection in vitro and in vivo are presented. In addition, this article reviews the epidemiology, pathological and clinicopathological findings, diagnosis, and control of EPE.

Comparative genome sequencing identifies a prophage-associated genomic island linked to host adaptation of Lawsonia intracellularis infections

Lawsonia intracellularis is an obligate intracellular bacterium and the causative agent of proliferative enteropathy (PE). The disease is endemic in pigs, emerging in horses and has also been reported in a variety of other animal species, including nonhuman primates. Comparing the whole genome sequences of a homologous porcine L. intracellularis isolate cultivated for 10 and 60 passages in vitro, we identified a 18-kb prophage-associated genomic island in the passage 10 (pathogenic variant) that was lost in the passage 60 (non-pathogenic variant). This chromosomal island comprises 15 genes downstream from the prophage DLP12 integrase gene. The prevalence of this genetic element was evaluated in 12 other L. intracellularis isolates and in 53 infected animals and was found to be conserved in all porcine isolates cultivated for up to 20 passages and was lost in isolates cultivated for more than 40 passages. Furthermore, the prophage region was also present in 26 fecal samples derived from pigs clinically affected with both acute and chronic forms of the disease. Nevertheless, equine L. intracellularis isolates evaluated did not harbor this genomic island regardless of the passage in vitro. Additionally, fecal samples from 21 clinically affected horses and four wild rabbits trapped in horse farms experiencing PE outbreaks did not show this prophage-associated island. Although the presence of this prophage-associated island was not essential for a virulent L. intracellularis phenotype, this genetic element was porcine isolate-specific and potentially contributed to the ecological specialization of this organism for the swine host.

Efficacy of a commercial live attenuated Lawsonia intracellularis vaccine in a large scale field trial in Korea

Purpose

Porcine proliferative enteropathy (PPE) is known as one of the most important risk factors causing economic losses in swine industry worldwide. This study was conducted to evaluate the efficacy of a commercial oral attenuated Lawsonia intracellularis vaccine (Enterisol Ileitis) against PPE under a commercial pig farm condition in Korea.

Materials and Methods

Thirty two-day-old 672 piglets were randomly allocated into vaccinated and control groups. All piglets in the vaccinated group were inoculated with a commercial attenuated L. intracellularis vaccine as following the manufacturer's instruction. Body weights of all pigs in both groups were measured on the vaccination day and 6, 14, and 20 weeks post vaccination and an average daily weight gain (ADWG) was calculated. Health status was observed biweekly during the whole trial.

Results

The vaccinated group showed significantly higher body weight (p<0.05) and ADWG (p<0.05) than those of the control group. The vaccinated group had significantly reduced impairments in activity, growth, defecation frequency, and stool hardness (p<0.05). Additional health benefits and improved weight gain by the vaccination produced a 4.2:1 return of investment, and the higher gross margin was $4.80 per pig.

Conclusion

Our finding suggests that the L. intracellularis vaccine program has effects on the substantial health and economic benefits in the Korean swine industry.

Laser microdissection coupled with RNA-seq analysis of porcine enterocytes infected with an obligate intracellular pathogen (Lawsonia intracellularis)

BACKGROUND

Lawsonia intracellularis is an obligate intracellular bacterium and the etiologic agent of proliferative enteropathy. The disease is endemic in pigs, emerging in horses and has been described in various other species including nonhuman primates. Cell proliferation is associated with bacterial replication in enterocyte cytoplasm, but the molecular basis of the host-pathogen interaction is unknown. We used laser capture microdissection coupled with RNA-seq technology to characterize the transcriptional responses of infected enterocytes and the host-pathogen interaction.

RESULTS

Proliferative enterocytes was associated with activation of transcription, protein biosynthesis and genes acting on the G1 phase of the host cell cycle (Rho family). The lack of differentiation in infected enterocytes was demonstrated by the repression of membrane transporters related to nutrient acquisition. The activation of the copper uptake transporter by infected enterocytes was associated with high expression of the Zn/Cu superoxide dismutase by L. intracellularis. This suggests that the intracellular bacteria incorporate intracytoplasmic copper and express a sophisticated mechanism to cope with oxidative stress.

CONCLUSIONS

The feasibility of coupling microdissection and RNA-seq was demonstrated by characterizing the host-bacterial interactions from a specific cell type in a heterogeneous tissue. High expression of L. intracellularis genes encoding hypothetical proteins and activation of host Rho genes infers the role of unrecognized bacterial cyclomodulins in the pathogenesis of proliferative enteropathy.

Equine proliferative enteropathy--a review of recent developments

Equine proliferative enteropathy (EPE) is a disease of foals caused by the obligate intracellular organism Lawsonia intracellularis. This emerging disease affects mainly weanling foals and causes fever, lethargy, peripheral oedema, diarrhoea, colic and weight loss. The diagnosis of EPE may be challenging and relies on the presence of hypoproteinaemia, thickening of segments of the small intestinal wall observed upon abdominal ultrasonography, positive serology and molecular detection of L. intracellularis in faeces. Although the clinical entity, diagnostic approach and treatment of EPE are well established and described, the epidemiology for this disease has remained largely unaddressed. This article focuses on new developments in the field of EPE, including epidemiology, pathophysiology, clinical signs, diagnosis, treatment and prevention.

The Summary is available in Chinese – see Supporting information.

Infection of sparrows (Passer domesticus) and different mice strains with Lawsonia intracellularis

The susceptibility of sparrows (Passer domesticus) and strains of mice (Swiss, BALB/c, C-57 and DB-A) to Lawsonia intracellularis infection was studied. Thirty-two sparrows were inoculated with pure culture of L. intracellularis and eleven received sham inoculum. Feces were collected on -1, 7, 14 and 21 days post infection (dpi) for detection of L. intracellularis by PCR. After 21 days, all sparrows were euthanized and the tissues processed for histology and immunohistochemistry (IHC). One hundred sixty mice of four different strains (n=40, per strain) were used. For each mouse strain, 16 animals received mucosa homogenate from a pig infected with L. intracellularis, 16 received pure culture of L. intracellularis and eight animals received sham inoculum. Two control and four inoculated mice from each group were euthanized on 7, 14, 21 and 28 dpi. Sections of intestine were collected for histologic analysis and IHC and pooled feces were collected for L. intracellularis PCR. None of the sparrows had any histologic lesions characteristic of proliferative enteropathy or antigen labeling by IHC. All sparrow fecal samples were negative by PCR. All mice strains studied had histopathological lesions typical of PE and IHC labeling consistent with L. intracellularis infection, especially those animals inoculated with pure culture. The most severe lesions were observed in DB-A and Swiss mice. Fecal shedding was detected in all mice strains, with peak at 14 dpi. We conclude that sparrows do not seem to be relevant in the epidemiology of L. intracellularis. The results showed variations in the lesions among the four mice strains used.

Immunological responses to vaccination following experimental Lawsonia intracellularis virulent challenge in pigs

Although a live attenuated vaccine has been used extensively to provide immunity against porcine proliferative enteropathy (PE) caused by Lawsonia intracellularis, the nature of the protective response is an area of considerable interest for the control of PE. Two trials investigated immune responses in pigs after oral and intramuscular (IM) vaccination followed by virulent L. intracellularis challenge. After an oral vaccination with 10(5.9) TCID50 organisms, significantly increased serum and mucosal secretions of IgM, IgG and higher mucosal TNF-α and TGF-β1 were detected by day 17, together with a trend towards higher levels of IFN-γ and IL-6. Pigs vaccinated IM produced elevated serum antibody titres but mucosal immune responses were not detected. After challenge with virulent L. intracellularis, non-vaccinated control pigs had higher PE lesion scores and excreted significantly higher numbers of L. intracellularis in faeces than the vaccinated pigs. Reduced intestinal pathology and faecal L. intracellularis shedding were evident in the vaccinated groups. The results indicated that protection was associated with mucosal cytokine and specific IgG and IgA responses after vaccination and that systemic antibody responses were boosted following challenge. However in the search for an immune correlate with protection, a causal association was not evident from a kinetic analysis of immune parameters in serum, ileal pathology and faecal shedding.

Association between faecal load of lawsonia intracellularis and pathological findings of proliferative enteropathy in pigs with diarrhoea

Background

The study was designed to investigate correlation between histological findings of Lawsonia intracellularis in porcine cases of diarrhoea and the quantitative detection of Lawsonia intracellularis in faeces. A total of 156 pigs (10 to 70 days post weaning) with diarrhoea were randomly selected from 20 herds: The pigs were subjected to necropsy, histopathology, immunohistochemistry and faecal quantification of Lawsonia intracellularis by real time PCR.

Results

The median Lawsonia intracellularis excretion was significantly higher in pigs with gross lesions of proliferative enteropathy (median excretion: 5.92 log₁₀ bacteria/g faeces) compared to pigs without gross lesions of proliferative enteropathy (median excretion: <3.3 log₁₀ bacteria/g faeces) (P<0.001). Spearman’s correlation coefficient between the measureable PE lesions and L. intracellularis excretion was 0.50 (P<0.001). A significantly increasing trend in Lawsonia intracellularis excretion level for increasing proliferative enteropathy histopathology and immunohistochemistry scores was demonstrated (P<0.001; P<0.001). Spearman’s correlation coefficient between the histopathology scores and L. intracellularis excretion was 0.67 (P<0.001). Spearman’s correlation coefficient between the IHC scores and L. intracellularis excretion was 0.77 (P<0.001).

Conclusions

The histological and quantitative PCR detection of Lawsonia intracellularis were correlated in pigs with diarrhoea. Overall the results suggest that clinically important levels for Lawsonia intracellularis excretion in faeces may be established. Such clinical threshold levels may be used in practice to confirm a diagnosis of Lawsonia intracellularis associated diarrhoea.

Association between average daily gain, faecal dry matter content and concentration of Lawsonia intracellularis in faeces

Background

The objective of this study was to investigate the association between average daily gain and the number of Lawsonia intracellularis bacteria in faeces of growing pigs with different levels of diarrhoea.

Methods

A longitudinal field study (n = 150 pigs) was performed in a Danish herd from day 29 to 47 post weaning. Every third day all pigs were weighed, subjected to a clinical examination and faecal samples were obtained. Faecal samples were subjected to dry matter determination and absolute quantification by PCR for L. intracellularis and porcine circovirus type 2 (PCV2). Association between average daily gain, faecal dry matter content, numbers of L. intracellularis bacteria and PCV2 genome copies in faeces was investigated in a multilevel mixed-effects linear model.

Results

Increasing numbers of L. intracellularis log₁₀ bacteria/g faeces were significantly associated with decreasing average daily gain (P < 0.001). The association was decreasing with increasing faecal dry matter content (P < 0.01). The number of PCV2 log₁₀ copies/g faeces was not significantly associated with average daily gain of the pigs (P > 0.5).

Conclusion

The results suggest a potential application of a PCR quantifying L. intracellularis in growing pigs. Faecal dry matter content must be taken into consideration in interpretation of such test results.