| Porcine proliferative enteropathy (PE) is an intestinal infectious disease characterized by thickening of the aboral small intestinal mucosa due to enterocyte proliferation associated with the presence of an intracellular bacterium, Lawsonia intracellularis. The overall goals of this project were to improve immunologic tests used for diagnosing PE and to characterize the mechanism of immune response and pathogenesis involved in L. intracellularis infection in pigs. The first section, a comparative study of different diagnostic tests, showed that immuno-based assays as serology and immunohistochemistry (IHC) are very accurate for diagnosing PE. Use of the immunoperoxidase monolayer assay (IPMA) serology test showed comparable results to the current fluorescent test, but also had some technical advantages. IPMA had sensitivity and specificity of 89 and 100%, respectively. A serologic follow-up using the IPMA technique revealed that gilts that recovered from the acute form of PE had serum antibodies up to three months after the beginning of the outbreak. The offspring of some seropositive sows at farrowing had maternal antibodies up to five weeks of age. Serum antibodies in growing-finishing pigs had low titers and were short-lived. In another study, new monoclonal and polyclonal antibodies against L. intracellularis were produced and characterized mainly for IHC use. For the subsequent two sections, the methodologies developed in each of the previous studies were used in the characterization of the immune response and pathogenesis involved in L. intracellularis infection in pigs. The second section describes the extraction and maintenance in vitro of a new American isolate of L. intracellularis that was demonstrated to be pathogenic in susceptible pigs. In addition, the humoral and cell-mediated immune responses and fecal shedding of infected and pigs exposed to a commercial vaccine was found to last much longer than expected. The pathogenesis study in the third section demonstrated that L. intracellularis infection in pigs is detected longer than histologic changes and that cell proliferation is not caused by reduction of apoptosis. The last study of the thesis showed that there are minor differences in the outer membrane protein profiles among L. intracellularis isolates extracted from different animal species. |
