A Cell Proliferation and Inflammatory Signature Is Induced by Lawsonia intracellularis Infection in Swine.

Lawsonia intracellularis causes porcine proliferative enteropathy. This is an enteric disease characterized by thickening of the wall of the ileum that leads to decreased growth of animals and diarrhea. In this study, we investigated the host response to L. intracellularis infection by performing transcriptomic and pathway analysis of intestinal tissue samples from groups of infected and noninfected animals at 14, 21, and 28 days postchallenge. At the peak of infection, when animals developed the most severe lesions, infected animals had higher levels of several gene transcripts involved in cellular proliferation and inflammation, including matrix metalloproteinase-7 (MMP7), transglutaminase-2 (TGM2), and oncostatin M (OSM). Histomorphology also revealed general features of intestinal inflammation. This study identified important pathways associated with the host response in developing and resolving lesions due to L. intracellularis infection.IMPORTANCELawsonia intracellularis is among the most important enteric pathogens of swine, and it can also infect other mammalian species. Much is still unknown regarding its pathogenesis and the host response, especially at the site of infection. In this study, we uncovered several novel genes and pathways associated with infection. Differentially expressed transcripts, in addition to histological changes in infected tissue, revealed striking similarities between L. intracellularis infection and cellular proliferation mechanisms described in some cancers and inflammatory diseases of the gastrointestinal tract. This research sheds important light into the pathogenesis of L. intracellularis and the host response associated with the lesions caused by infection.

The effects of zinc amino acid complex supplementation on the porcine host response to Lawsonia intracellularis infection.

Lawsonia intracellularis is among the most important enteric pathogens of swine and antibiotic alternatives are needed to help mitigate the negative effects of infection. Zinc is an essential trace mineral known to be crucial for maintaining intestinal barrier function and proper immune response. In this study, we investigated the porcine host response to L. intracellularis infection when supplemented with a zinc-amino acid complex, a form of zinc that can lead to greater bioavailability when compared to traditional inorganic forms of zinc. Our results show that a zinc-amino acid complex supplementation with a final concentration of 125 ppm of zinc in feed significantly (p < 0.05) decreased the number of animals with lesions and severity of lesions caused by L. intracellularis. Animals supplemented with the zinc-amino acid complex also exhibited a significantly (p < 0.05) earlier onset of seroconversion as well as an increased number of T cells in infected and non-infected intestinal tissue. This study demonstrated that this zinc-amino acid complex aids the host in responding to L. intracellularis infection and may be a new approach to help minimize negative effects of disease.

Evaluation of lincomycin in drinking water for treatment of induced porcine proliferative enteropathy using a Swine challenge model.

A single-location, challenge-model study was conducted to evaluate the effectiveness of lincomycin against porcine proliferative enteropathy when administered through the drinking water at 125 and 250 mg/gallon. The primary variables of interest were pig removal rate, diarrhea scores, demeanor scores, and abdominal appearance scores. Ancillary performance variables examined included average daily feed intake, average daily gain, and feed per gain. After a 3-day acclimation period, pigs were challenged on 2 consecutive days with a mucosal homogenate containing a total dose of 1.4 x 10(9) cells of Lawsonia intracellularis. Five days later, when porcine proliferative enteropathy was well established, drinking water medicated with 125 mg (L125) or 250 mg (L250) lincomycin/gallon was provided to two groups of pigs for 10 days. Pigs were observed for 13 days following the treatment period. A third group of pigs served as controls and received unmedicated drinking water throughout the study. The L250 group experienced a significantly lower (P < .05) pig removal rate than the control group over the 23-day observation period. Additionally, for every primary variable, the L250 group experienced a significantly decreased (P < .01) number of abnormal days compared with the control group. The L125 group showed a significant reduction (P < .05) in abnormal demeanor and abnormal abdominal appearance scores compared with controls.

Validation of an immunoperoxidase monolayer assay as a serologic test for porcine proliferative enteropathy.

The sensitivity and specificity of an immunoperoxidase monolayer assay (IPMA) was evaluated in a blind serologic study of a group of disease-free pigs and a group of pigs experimentally infected with intestinal homogenate containing Lawsonia intracellularis organisms. Sixty pigs from the control group were kept in the source farm, and another 60 animals were transferred to an isolation unit aid challenged intragastrically. All animals were bled before and 21 days after challenge. Fecal samples were collected on the same dates. The IPMA results were tested for sensitivity and specificity in a 2 x 2 table using the challenged and nonchallenged status as gold standard. Sensitivity and specificity were evaluated for different cutoff points (serum dilutions). Specificities of 100% were obtained for all the serum dilutions tested (1:15, 1:30, 1:60, and 1:120). The sensitivity levels were 90.7%, 88.9%, 81.5%, and 75.9% for the serum dilutions 1:15, 1:30, 1:60, and 1:120, respectively. The sensitivity of the dilution 1:15 was slightly, but not significantly, higher than the dilution currently used as the cutoff point (1:30). Cross-reactivity of the IPMA test was evaluated using sera from pigs experimentally inoculated with Brachyspira pilosicoli and various Campylobacter species. All these samples were negative. Sera samples from 3 porcine proliferative enteropathy known negative populations, 40 growing pigs from 2 commercial farms and a group of 6 cesarean-derived and colostrum-deprived pigs, also tested negative by IPMA. The IPMA serologic test with the cutoff point of 1:30 showed specificity of 100% and sensitivity close to 90% and, therefore, is an appropriate diagnostic test for herd screening but not for diagnosing PPE on the individual level.

A comparative study of an indirect fluorescent antibody test and an immunoperoxidase monolayer assay for the diagnosis of porcine proliferative enteropathy.

The currently used indirect fluorescent antibody test (IFAT) for the detection of antibodies against porcine proliferative enteropathy (PPE) was compared to an immunoperoxidase monolayer assay (IPMA). Serum samples used in this comparison were collected from 5-week-old pigs on day 0 (pre-experimental challenge) and on days 7, 14, 21, and 28 after oral inoculation with intestinal homogenate from pigs affected by PPE (28 challenged pigs) and sucrose phosphate glutamate solution (2 control pigs). All animals were euthanized 4 weeks after inoculation. Immunohistochemistry staining was applied to formalin-fixed, paraffin-embedded sections of ileum for the detection of Lawsonia intracellularis antigen. The serology results with each method agreed in all samples, except on days 0 and 7 in 1 control animal, which was positive by IPMA, but negative by IFAT. The percentage of agreement between IFAT and IPMA was 98.6%.

Comparison of different methods for diagnosis of porcine proliferative enteropathy.

The objectives of this study were: (1) to compare 2 methods of serology; (2) to compare 3 histologic techniques; and (3) to compare 2 methods of detecting shedding in pigs experimentally challenged with Lawsonia intracellularis. The sensitivities of these tests were determined by the detection of infection. Forty 5-week-old pigs were inoculated on day 0 with intestinal homogenate from pigs with proliferative enteropathy (PE). Clinical evaluation was done on day 7 and daily from day 14 to 28 postinoculation. Fecal shedding of L. intracellularis was monitored by use of polymerase chain reaction (PCR) analysis and immunoperoxidase staining at 7-day intervals. Serum was obtained on days 0 and 28 for serologic testing by glass slide and tissue culture indirect fluorescent antibody tests. At euthanasia on day 28, gross intestinal lesions were evaluated and ileum samples collected for histologic analyses. Ileal histologic sections from each animal were stained by hematoxylin and eosin, Warthin-Starry silver stain, and immunohistochemistry (IHC). Of the 40 pigs, 36 had gross lesions typical of PE at necropsy. The percentage of agreement between the 2 serologic methods was 94.4%. Immunoperoxidase stain of fecal smears was more sensitive than PCR for detecting fecal shedding, especially on day 21 (89.5% and 60.5%, respectively) and day 28 (59.4% and 37.5%, respectively) post-inoculation. The IHC stain was much more sensitive for detecting infection than the routinely used hematoxylin and eosin and Warthin-Starry silver stains. In conclusion, in experimentally infected pigs, both serologic methods were appropriate techniques for detecting infection. For fecal samples, PCR has low sensitivity. Immunohistochemistry is the best diagnostic tool for formalin-fixed samples.