Fatal outbreaks of proliferative enteritis caused by Lawsonia intracellularis in young colony-raised rhesus macaques

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.

Prevalence and associated risk factors for Lawsonia intracellularis infection in farmed rabbits: A serological and molecular cross-sectional study in South Korea

Lawsonia intracellularis is the etiological agent of proliferative enteropathy, which is globally considered an important enteric disease in pigs and horses. Experimental studies suggest that the organism spreads by subclinical infection of many animals, including rabbits. Despite the importance of rabbits in the epidemiology of L. intracellularis, the extent of exposure to L. intracellularis in the rabbit population is poorly defined and remains unclear. The objective of this cross-sectional study was to investigate the seroprevalence and shedding of L. intracellularis in farmed rabbits. Furthermore, we aimed to identify risk factors associated with seropositivity. Sera from the rabbits were used to measure L. intracellularis-specific antibodies by immunoperoxidase monolayer assay, and rectal swabs were used to detect L. intracellularis DNA using a real-time PCR assay. Antibodies against L. intracellularis were detected in 12.3% of farms (20/163) and 6.3% of rabbits (49/774). Lawsonia intracellularis DNA in rectal swabs was detected in 3.8% of farms (6/156) and 1.2% of rabbits (8/667). The risk factor analysis showed that the presence of pigs or horses on the farm or the neighboring farm was associated with an increase in the risk of seropositivity (p < 0.05). We observed significantly increased odds of positivity for L. intracellularis in rabbits with a history of digestive trouble (diarrhea) on the farm during the 3 months before the samples were obtained (p < 0.05). Collectively, these findings demonstrated that L. intracellularis infection was evident among farmed rabbits and that rabbits might serve as an important reservoir for L. intracellularis epidemiology.

Evaluation of host and bacterial gene modulation during Lawsonia intracellularis infection in immunocompetent C57BL/6 mouse model

BACKGROUND

Proliferative enteritis caused by Lawsonia intracellularis undermines the economic stability of the swine industry worldwide. The development of cost-effective animal models to study the pathophysiology of the disease will help develop strategies to counter this bacterium.

OBJECTIVES

This study focused on establishing a model of gastrointestinal (GI) infection of L. intracellularis in C57BL/6 mice to evaluate the disease progression and lesions of proliferative enteropathy (PE) in murine GI tissue.

METHODS

We assessed the murine mucosal and cell-mediated immune responses generated in response to inoculation with L. intracellularis.

RESULTS

The mice developed characteristic lesions of the disease and shed L. intracellularis in the feces following oral inoculation with 5 × l07 bacteria. An increase in L. intracellularis 16s rRNA and groEL copies in the intestine of infected mice indicated intestinal dissemination of the bacteria. The C57BL/6 mice appeared capable of modulating humoral and cell-mediated immune responses to L. intracellularis infection. Notably, the expression of genes for the vitamin B12 receptor and for secreted and membrane-bound mucins were downregulated in L. intracellularis -infected mice. Furthermore, L. intracellularis colonization of the mouse intestine was confirmed by the immunohistochemistry and western blot analyses.

CONCLUSIONS

This is the first study demonstrating the contributions of bacterial chaperonin and host nutrient genes to PE using an immunocompetent mouse model. This mouse infection model may serve as a platform from which to study L. intracellularis infection and develop potential vaccination and therapeutic strategies to treat PE.

Research Relevant Conditions and Pathology in Nonhuman Primates

Biomedical research involving animal models continues to provide important insights into disease pathogenesis and treatment of diseases that impact human health. In particular, nonhuman primates (NHPs) have been used extensively in translational research due to their phylogenetic proximity to humans and similarities to disease pathogenesis and treatment responses as assessed in clinical trials. Microscopic changes in tissues remain a significant endpoint in studies involving these models. Spontaneous, expected (ie, incidental or background) histopathologic changes are commonly encountered and influenced by species, genetic variations, age, and geographical origin of animals, including exposure to infectious or parasitic agents. Often, the background findings confound study-related changes, because numbers of NHPs used in research are limited by animal welfare and other considerations. Moreover, background findings in NHPs can be exacerbated by experimental conditions such as treatment with xenobiotics (eg, infectious morphological changes related to immunosuppressive therapy). This review and summary of research-relevant conditions and pathology in rhesus and cynomolgus macaques, baboons, African green monkeys, common marmosets, tamarins, and squirrel and owl monkeys aims to improve the interpretation and validity of NHP studies.

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.

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.

Metagenomic sequencing of clinical samples reveals a single widespread clone of Lawsonia intracellularis responsible for porcine proliferative enteropathy

Lawsonia intracellularis is a Gram-negative obligate intracellular bacterium that is the aetiological agent of proliferative enteropathy (PE), a common intestinal disease of major economic importance in pigs and other animal species. To date, progress in understanding the biology of L. intracellularis for improved disease control has been hampered by the inability to culture the organism in vitro. In particular, our understanding of the genomic diversity and population structure of clinical L. intercellularis is very limited. Here, we utilized a metagenomic shotgun approach to directly sequence and assemble 21 L. intracellularis genomes from faecal and ileum samples of infected pigs and horses across three continents. Phylogenetic analysis revealed a genetically monomorphic clonal lineage responsible for infections in pigs, with distinct subtypes associated with infections in horses. The genome was highly conserved, with 94 % of genes shared by all isolates and a very small accessory genome made up of only 84 genes across all sequenced strains. In part, the accessory genome was represented by regions with a high density of SNPs, indicative of recombination events importing novel gene alleles. In summary, our analysis provides the first view of the population structure for L. intracellularis, revealing a single major lineage associated with disease of pigs. The limited diversity and broad geographical distribution suggest the recent emergence and clonal expansion of an important livestock pathogen.

Social style and resilience of macaques' networks, a theoretical investigation

Group-living animals rely on efficient transmission of information for optimal exploitation of their habitat. How efficient and resilient a network is depend on its structure, which is a consequence of the social interactions of the individuals that comprise the network. In macaques, network structure differs according to dominance style. Networks of intolerant species are more modular, more centralized, and less connected than those of tolerant ones. Given these structural differences, networks of intolerant species are potentially more vulnerable to fragmentation and decreased information transmission when central individuals disappear. Here we studied network resilience and efficiency in artificial societies of macaques. The networks were produced with an individual-based model that has been shown to reproduce the structural features of networks of tolerant and intolerant macaques. To study network resilience, we deleted either central individuals or individuals at random and studied the effects of these deletions on network cohesiveness and efficiency. The deletion of central individuals had more negative effects than random deletions from the networks of both tolerant and intolerant artificial societies. Central individuals thus appeared to aid in the maintenance of network cohesiveness and efficiency. Further, the networks of both intolerant and tolerant societies appeared to be robust to the loss of individuals, as network fragmentation was never observed. Our results suggest that despite differences in network structure, networks of tolerant and intolerant macaques may be equally resilient.

Lawsonia intracellularis in the feces of wild rodents and stray cats captured around equine farms

BACKGROUND

Proliferative enteropathy is a global enteric disease of particular importance in pigs. The causative bacterium, Lawsonia intracellularis, has a wide range of susceptible host species. Recently, L. intracellularis has been recognized as an etiologic agent of an emerging enteric disease in foals called equine proliferative enteropathy (EPE). The presence of L. intracellularis in nonruminant wildlife has raised questions regarding the role of these species in EPE transmission.

RESULTS

This study investigated exposure to L. intracellularis in wild rodents and feral cats from eight farms with confirmed EPE. Serum (42) and fecal (40) samples from resident foals and fecal samples (131), intestinal mucosa tissues (14), and mesenteric lymph nodes (14) from wild and feral animals were collected for the evaluation of the farm status and the molecular detection of L. intracellularis following the diagnosis of EPE in index cases. Fresh feces from wild rodents and feral cats were collected from the ground while walking the premises or after trapping the animals using live traps. A total of 3 brown rats, 7 house mice, 1 striped field mouse, 2 grey red-backed voles, and 3 feral cats showed evidence of prior exposure to L. intracellularis.

CONCLUSIONS

Our data add to increasing evidence demonstrating the potential for L. intracellularis transmission and infection in wild rodents and feral cats and provide possible evidence of interspecies transmission. The exposure of wild rodents and feral cats provides potential evidence for the spillover of L. intracellularis to wildlife species and raises the question of spillback to horses. Additionally, these animals may represent an indicator of environmental exposure or may be actively involved in the transmission of L. intracellularis to foals by acting as potential reservoir/amplifier hosts. This study is the first to demonstrate the magnitude of L. intracellularis shedding in the feces of wild rodents and feral cats and to indicate the significant infection risk that wild rodents and feral cats pose to naïve horses in South Korea.

PREVALENCE OF ANTIBODY TO AND DNA OF LAWSONIA INTRACELLULARIS IN SAMPLES FROM WILD ANIMALS IN KOREA

We evaluated the prevalence of Lawsonia intracellularis infection in three wild animal species in Korea; the Korean water deer ( Hydropotes inermis ), Siberian roe deer ( Capreolus pygargus ), and raccoon dogs ( Nyctereutes procyonoides ). We collected 136 sera and 109 fecal samples from individuals in 10 Wildlife Rescue and Conservation Centers. Serum samples were tested for anti- L. intracellularis antibodies using a blocking enzyme-linked immunosorbent assay (bELISA), and fecal samples were subjected to a real-time PCR assay for L. intracellularis . Thirty-five (25.7%) sera and 36 (33.0%) fecal samples were positive. We found a higher proportion of positive sera (64.7%, χ²=15.439, P<0.01) and feces (58.8%, χ²=6.126, P<0.05) in raccoon dogs (χ²=11.855, P<0.01) than in the other species (20% positive sera and 29% positive feces in Korean water deer; 20% positive sera and 25% positive feces in Siberian roe deer). Our data indicate infection by L. intracellularis in Korean water deer, Siberian roe deer, and raccoon dogs throughout the country. It is imperative to know whether these infected animal species are natural hosts for L. intracellularis in addition to domestic pigs ( Sus scrofa domesticus).

Preparation and Characterization of Polyclonal and Monoclonal Antibodies against Lawsonia Intracellularis

Proliferative enteropathy is an intestinal infectious disease caused by the obligate intracellular bacterium Lawsonia intracellularis. Immunohistochemistry staining has superior sensitivity over hematoxylin and eosin and silver staining for detecting L. intracellularis in histological sections. A L. intracellularis—specific monoclonal antibody (MAb) produced in the UK (IG4 MAb) has been described in the literature. However, no monoclonal or polyclonal antibodies are commercially available. Therefore, the objective of this study was to produce and characterize new polyclonal and monoclonal antibodies against L. intracellularis that are suitable for diagnostic use. The new monoclonal (2001 MAb) and polyclonal antibodies (1999 PAb) were compared with the IG4 MAb using Western blot analysis of outer membrane proteins (OMPs) of 6 L. intracellularis isolates, Bilophila wadsworthia and Brachyspira hyodysenteriae and using immunohistochemistry of known positive and negative histologic samples and pure cultures of L. intracellularis, B. wadsworthia, B. hyodysenteriae, Salmonella choleraesuis, S. typhimurium, and Escherichia coli K88. Immunogold staining using 2001 MAb was performed to show the specificity of the antibody against an L. intracellularis surface protein. Western blot analysis showed that the 2001 MAb targeted an OMP of 77 kD, which made it different from the IG4 MAb that targeted an 18-kD OMP. The immunogold stain demonstrated the specificity of the 2001 MAb to a surface protein of L. intracellularis. The polyclonal antibody (1999 PAb) targeted 5 OMPs (77, 69, 54, 42, and 36 kD). Both the 2001 MAb and 1999 PAb stained known positive, but not negative, histologic samples. Both the 2001 MAb and 1999 PAb reacted with a pure culture of L. intracellularis but not with any other common enteric pathogens. These two new antibodies will be useful for immunodiagnosis of L. intracellularis.

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.

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.

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.

Evidence of host adaptation in Lawsonia intracellularis infections

Background

Lawsonia intracellularis is the causative agent of proliferative enteropathy, an endemic disease in pigs and an emerging concern in horses. Enterocyte hyperplasia is a common lesion in every case but there are differences regarding clinical and pathological presentations among affected species. We hypothesize that host susceptibility to L. intracellularis infection depends on the species of origin of the bacterial isolate. The objective of this study was to evaluate the susceptibilities of pigs and horses to L. intracellularis infection using either a porcine or an equine isolate.

Materials and methods

Twelve foals and eighteen pigs were equally divided into three groups and infected with either a porcine or an equine isolate (10⁹L. Intracellularis/challenged animal), and a saline solution (negative control group). The animals were monitored regarding clinical signs, average of daily weight gain, fecal shedding of the bacteria by PCR and humoral serological response.

Results

Foals infected with the equine isolate developed moderate to severe clinical signs and maintained a lower average of weight gain compared to control foals. Fecal quantitative PCR in equine isolate-infected foals revealed higher amounts of bacterial DNA associated with longer duration of shedding compared with porcine isolate-infected foals. All four foals infected with the equine isolate demonstrated higher IgG titers in the serum compared with porcine isolate-infected foals. In the pig trial, diarrhea and seroconversion were only observed in animals infected with the porcine isolate. Pathological changes typical of proliferative enteropathy were observed in the necropsied foal infected with equine isolate and in the two necropsied pigs infected with the porcine isolate.

Conclusions

Evident clinical signs, longer periods of bacterial shedding and stronger serologic immune responses were observed in animals infected with species-specific isolates. These results show that host susceptibility is driven by the origin of the isolated L. intracellularis strain.

Porcine proliferative enteropathy: an important disease with questions remaining to be solved

Proliferative enteropathy caused by the intracellular bacterium Lawsonia intracellularis is an endemic disease with high herd prevalences reported worldwide. The infection has a considerable impact on pig production and herd economics and, with the development of new diagnostic techniques, L. intracellularis is being identified in an increasing number of pig herds and a wider range of species. This paper reviews current knowledge of the disease, with a focus on the epidemiology in pigs. The prevalence of infection, transmission, predisposing factors, microbial features, pathogenesis, clinical signs, diagnosis, treatment and control are discussed. The disease is mainly controlled by antibiotic treatment and vaccination at herd level. In the development of effective measures to prevent the spread of the infection, increased knowledge of the transmission and persistence of the microorganism are crucial.

Proliferative enteropathy involving Lawsonia intracellularis infection in rabbits (Oryctlagus cuniculus)

Five rabbits suffering from diarrhea were diagnosed with proliferative enteropathy (PE). Histopathology revealed a thickened mucosa consisting of hyperplastic intestinal epithelium and infiltration of inflammatory cells mainly consisted of macrophages. In the affected epithelial cytoplasm, numerous curved bacillus-like organisms were observed in the Warthin-Starry silver stain and electron microscopy observation. In polymerase chain reactions, Lawsonia intracellularis-specific DNA fragment were amplified from affected ileal tissue extracted DNA in each case and present 5 cases were confirmed to be L. intracellularis infection. Serum collected from the affected rabbit was immunohistochemically reactive with L. intracellularis in tissue sections from pigs with porcine proliferative enteropathy, as well as with tissue sections from the five affected rabbits. Thus, serum obtained from the affected rabbit may be applicable to immunohistochemical detection for L. intracellularis infection in other species.

Proliferative enteropathy: a global enteric disease of pigs caused byLawsonia intracellularis

Proliferative enteropathy (PE; ileitis) is a common intestinal disease affecting susceptible pigs raised under various management systems around the world. Major developments in the understanding of PE and its causative agent,Lawsonia intracellularis, have occurred that have led to advances in the detection of this disease and methods to control and prevent it. Diagnostic tools that have improved overall detection and early onset of PE in pigs include various serological and molecular-based assays. Histological tests such as immunohistochemistry continue to be the gold standard in confirmingLawsonia-specific lesions in pigspost mortem. Despite extreme difficulties in isolatingL. intracellularis, innovations in the cultivation and the development of pure culture challenge models, have opened doors to better characterization of the pathogenesis of PE throughin vivoandin vitro L. intracellularis–host interactions. Advancements in molecular research such as the genetic sequencing of the entireLawsoniagenome have provided ways to identify various immunogens, metabolic pathways and methods for understanding the epidemiology of this organism. The determinations of immunological responsiveness in pigs to virulent and attenuated isolates ofL. intracellularisand identification of various immunogens have led to progress in vaccine development.

In vitro cultivation and partial characterization of Lawsonia intracellularis from a Japanese field case of porcine proliferative enteropathy

Lawsonia intracellularis isolated from a Japanese field case of porcine proliferative enteropathy (PPE) was cultivated and partially characterized. The bacterial cells isolated from the intestinal mucosa of a pig suffering from the acute form of PPE were used to inoculate rat small intestine cells (IEC-18) and human epithelial cells (HEp-2). Infected foci, which were stained with L. intracellularis-specific rabbit antiserum, were observed in the cell culture at 5 days post inoculation. The DNA sequence of several genes in the Japanese isolate had high similarity with those of the L. intracellularis type strain, suggesting the genetically close relationship of the two strains. This is the first report describing the cultivation and partial characterization of L. intracellularis originated in Japan.

Polymorphisms in equine immune response genes and their associations with infections

Polymorphic markers identified in the horse genes encoding the interleukin 12 p40 subunit, interferon gamma, tumor necrosis factor receptor 1, and inducible nitric oxide synthase were identified and tested, along with additional markers, for associations with two important horse infections: Rhodococcus equi and Lawsonia intracellularis. Eight immune response-related and 14 microsatellite loci covering 12 out of 31 equine autosomes were used for the association analysis. Markers located on horse Chromosomes Eca10 and 15 were significantly associated with the presence of high numbers of R. equi in transtracheal aspirates. Significant associations of markers located on Eca9, 15, and 21 with fecal shedding of Lawsonia intracellularis were found. Marginal associations with tumor necrosis factor alpha, interferon gamma, and other genes suggested that variations in immune response-related genes could underlie the phenotypic variation observed.

LsaA, an antigen involved in cell attachment and invasion, is expressed by Lawsonia intracellularis during infection in vitro and in vivo

Lawsonia intracellularis has been identified recently as the etiological agent of proliferative enteropathies, which are characterized by intestinal epithelial hyperplasia and associated moderate immune responses. This disease complex has been reported in a broad range of animals, prevalently in pigs, and L. intracellularis has been linked with ulcerative colitis in humans. L. intracellularis is an obligate intracellular bacterium, and the pathogenic mechanisms used to cause disease are unknown. Using in vitro-grown organisms as a source of genomic DNA, we identified a Lawsonia gene which encodes a surface antigen, LsaA (for Lawsonia surface antigen), associated with attachment to and entry into cells. The deduced amino acid sequence of this protein showed some similarity to members of a novel protein family identified in a number of other bacterial pathogens but for which roles are not fully defined. Transcription of this gene was detected by reverse transcription-PCR in L. intracellularis grown in vitro in IEC18 cells and in bacteria present in ileal tissue from infected animals. Immunohistochemistry with specific monoclonal antibody and immunoblotting with sera from infected animals demonstrated that LsaA protein is synthesized by L. intracellularis during infection. Expression of this gene during infection in vitro and in vivo suggests that this surface antigen is involved during infection, and phenotypic analysis indicated a role during L. intracellularis attachment to and entry into intestinal epithelial cells

Colonic infection by Bilophila wadsworthia in pigs

Bilophila wadsworthia is a common inhabitant of the human colon and has been associated with appendicitis and other local sites of inflammation in humans. Challenge-exposure or prevalence studies in laboratory and other animals have not been reported. B. wadsworthia is closely related phylogenetically to Desulfovibrio sp. and Lawsonia intracellularis, which are considered colon pathogens. We developed a PCR specific for B. wadsworthia DNA. Samples of bacterial DNA extracted from the feces of pigs on six farms in Australia and four farms in Venezuela were examined. Specific DNA of B. wadsworthia was detected in the feces of 58 of 161 Australian and 2 of 45 Venezuelan pigs, results comprising 100% of the neonatal pigs, 15% of the weaned grower pigs, and 27% of the adult sows tested. Single-stranded conformational polymorphism analysis of PCR product DNA derived from pigs or from known human strains showed an identical pattern. Histologic examination of the intestines of weaned B. wadsworthia-positive pigs found no or minor specific lesions in the small and large intestines, respectively. B. wadsworthia is apparently a common infection in neonatal pigs, but its prevalence decreases after weaning. The possible role of B. wadsworthia as an infection in animals and in human colons requires further study.

A member of the delta subgroup of proteobacteria from a pyogenic liver abscess is a typical sulfate reducer of the genus Desulfovibrio

Strain FH26001/95 (ATCC 700045) was previously isolated from a pyogenic liver abscess from a human. Comparative 16S rRNA gene sequence analysis showed that this strain is related to members of the delta subgroup of the proteobacteria, within a cluster of sulfate-reducing bacteria (Desulfovibrio spp.) and non-sulfate-reducing bacteria (Bilophila wadsworthia and Lawsonia spp.). The phenotype of strain FH26001/95 was found to be typical of members of the genus Desulfovibrio. Growth and substrate transformations were possible at oxygen concentrations of 2 to 5% (vol/vol) but not at oxygen concentrations of 21% (vol/vol) in air. Its isolation from an infection in a human suggests that some members of the genus Desulfovibrio can be considered opportunistic pathogens.

Gamma interferon influences intestinal epithelial hyperplasia caused by Lawsonia intracellularis infection in mice

Lawsonia intracellularis is a recently identified bacterial pathogen which causes disease in a broad range of animals. Invasion of intestinal epithelial cells and the resultant hyperplasia of infected cells are central processes in disease pathogenesis. In this study, we aimed to establish whether immunocompetent mice were susceptible to infection and whether gamma interferon (IFN-gamma) contributed to the pathogenesis of infection. Wild-type 129-Sv-Ev mice (129 mice) and IFN-gamma receptor knockout mice based on the 129 background (IFN-gammaR(-)) were challenged orally with approximately 5.5 x 10(7) L. intracellularis cells. Both 129 and IFN-gammaR(-) mice became infected, although the extent of infection (as determined by the proportion of infected crypts) was substantially lower in 129 mice than in IFN-gammaR(-) mice. Despite these differences, infected crypts showed characteristics typical of proliferative enteropathies of other animals, i.e., intracellular colonization of epithelial cells by L. intracellularis with resultant epithelial hyperplasia. Infection in 129 mice was cleared between days 21 and 28 postchallenge, whereas infection in IFN-gammaR(-) mice was evident in 100% of animals from day 21 onward. Additionally, in IFN-gammaR(-) mice the infection was so extensive that fatalities resulted. IFN-gamma therefore plays a significant role in limiting intracellular infection and increased cellular proliferation associated with L. intracellularis. L. intracellularis infection is generally associated with modest cellular infiltration; therefore, further comparative examinations will be necessary to determine pathogenicity factors and define the role of IFN-gamma in controlling this infection.

Equine proliferative enteropathy: a cause of weight loss, colic, diarrhoea and hypoproteinaemia in foals on three breeding farms in Canada

Proliferative enteropathy (PE) is a transmissible enteric disease caused by Lawsonia intracellularis. An outbreak of equine PE was diagnosed in foals from 3 breeding farms. Most foals had been weaned prior to the appearance of clinical signs, which included depression, rapid and marked weight loss, subcutaneous oedema, diarrhoea and colic. Poor body condition with a rough haircoat and a potbellied appearance were common findings in affected foals. Respiratory tract infection, dermatitis and intestinal parasitism were also found in some foals. Haematological and plasma biochemical abnormalities included hypoproteinaemia, transient leucocytosis, anaemia and increased serum creatinine kinase concentration. Postmortem diagnosis of PE was confirmed on 4 foals based on the presence of characteristic intracellular bacteria within the apical cytoplasm of proliferating crypt epithelial cells of the intestinal mucosa, using silver stains, and by results of PCR analysis and immunohistochemistry. Antemortem diagnosis of equine PE was based on the clinical signs, hypoproteinaemia and the exclusion of common enteric infections. Faecal PCR analysis was positive for the presence of L. intracellularis in 6 of 18 foals tested while the serum of all 7 foals with PE serologically evaluated had antibodies against L. intracellularis. Most foals were treated with erythromycin estolate alone or combined with rifampin for a minimum of 21 days. Additional symptomatic treatments were administered when indicated. All but one foal treated with erythromycin survived the infection. This study indicates that equine PE should be included in the differential diagnosis of outbreaks of rapid weight loss, diarrhoea, colic and hypoproteinaemia in weanling foals.