Abstract
Lawsonia intracellularis is endemic to swine herds worldwide, however much is still unknown regarding its impact on intestinal function. Thus, this study aimed to characterize the impact of L. intracellularis on digestive function, and how vaccination mitigates these impacts. Thirty-six L. intracellularis negative barrows were assigned to treatment groups (n = 12/trt): (1) nonvaccinated, L. intracellularis negative (NC); (2) nonvaccinated, L intracellularis challenged (PC); and (3) L. intracellularis challenged, vaccinated (Enterisol® Ileitis, Boehringer Ingelheim) 7 weeks pre-challenge (VAC). On days post-inoculation (dpi) 0 PC and VAC pigs were inoculated with L. intracellularis. From dpi 19–21 fecal samples were collected for apparent total tract digestibility (ATTD) and at dpi 21, pigs were euthanized for sample collection. Post-inoculation, ADG was reduced in PC pigs compared with NC (41%, P < 0.001) and VAC (25%, P < 0.001) pigs. Ileal gross lesion severity was greater in PC pigs compared with NC (P = 0.003) and VAC (P = 0.018) pigs. Dry matter, organic matter, nitrogen, and energy ATTD were reduced in PC pigs compared with NC pigs (P ≤ 0.001 for all). RNAscope in situ hybridization revealed abolition of sucrase-isomaltase transcript in the ileum of PC pigs compared with NC and VAC pigs (P < 0.01). Conversely, abundance of stem cell signaling markers Wnt3, Hes1, and p27Kip1 were increased in PC pigs compared with NC pigs (P ≤ 0.085). Taken together, these data demonstrate that reduced digestibility during L. intracellularis challenge is partially driven by abolition of digestive machinery in lesioned tissue. Further, vaccination mitigated several of these effects, likely from lower bacterial burden and reduced disease severity.
Highlights
Understanding and managing sub-clinical and clinical pathogenic disease in swine remains a formidable challenge for pork producers worldwide
There were three pigs in the NC group that had detectable fecal shedding at necropsy (415, 230 and 250 genomic copies/mL), this was likely either a false positive or due to contamination at necropsy, as these pigs did not test positive by any other parameters
NC pigs remained negative and fecal shedding of organism continued to increase over the experimental period for PC pigs (6.4 log10 genomic copies/mL at dpi 21)
Summary
Understanding and managing sub-clinical and clinical pathogenic disease in swine remains a formidable challenge for pork producers worldwide. One enteric pathogen of particular concern to pork producers is Lawsonia intracellularis, an intracellular bacterium responsible for proliferative enteropathy in growing pigs [1]. The bacterium is endemic to swine farms, with worldwide farm. Due to its obligate intracellular nature, understanding the interaction of L. intracellularis with the host is critical to fully understanding pathogenesis of this disease. The bacterium primarily infects enterocytes of the terminal ileum, infected enterocytes may extend proximally into the jejunum or distally into the large intestine [5, 6]. Upon establishing within infected epithelial enterocytes, L. intracellularis induces proliferation of undifferentiated epithelial cells, resulting in mucosal hyperplasia [1].
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