Enteric Diseases of Swine and Cattle: Prevention, Control and Food Safety

NON-TECHNICAL SUMMARY: Even though most people in the US feel that their food is safe, foodborne illnesses are a serious problem that affects and concerns everyone. Diarrheal diseases are economically important causes of production losses to livestock producers. This project will enhance pork and beef production and food safety by: providing information on mechanisms used by enteric pathogens to cause disease in humans and livestock; identifying ways in which these agents are transmitted to humans, improving the diagnosis of enteric pathogens in livestock, their environment, and our food.
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APPROACH: <BR> 1. AZ and MN will exchange Lawsonia isolates and monoclonal antibodies to determine antigen cross-reactivity between strains and to identify neutralizing-sensitive epitopes of field isolates. NE will collaborate with MN on the development of a laboratory mouse model of proliferative enteropathy caused by Lawsonia intracellularis. <BR>OH will collaborate with NE, IA, and MN to improve the efficacy of current rotavirus vaccines and develop new vaccines (virus-like particles, DNA vaccines, and new adjuvant and deliver systems). OH will collaborate with IA and MN in comparing immunologic reagents and assays to quantitate humoral and cellular immune responses in swine. <BR> The NC-1007 committee will assemble a lay document describing major advances in knowledge and technology through research by participating states, with livestock producers, veterinary professionals, and consumers as the target audience.
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PROGRESS: 2002/10 TO 2007/09<BR>
Molecular epidemiologic typing of L. intracellularis. New knowledge regarding infection and transmission of L. intracellularis was obtained using the variable number tandem repeat (VNTR) genetic typing technique. Though Lawsonia is antigenically conserved, there is genetic variation that exists between isolates. No variation was observed between isolates obtained from various clinical types of proliferative enteropathy within a flow, including acute, chronic, and subclinical samples. Slight variation between isolates from different geographic locations was detected, though those variations were no greater between isolates from different continents than between isolates from different Midwestern U.S. pig farms. Marked variation exists, however, between isolates from pig and certain non-pig sources. These variations may be used to track outbreaks occurring in pigs, horses, or other animals. In vitro activity of six antimicrobial agents against ten L. intracellularis isolates from the U.S. and Europe. To achieve the best outcome for treatment and control of proliferative enteropathy, the selection of correct antimicrobials is a critical decision. However, little information on antimicrobial sensitivities against L. intracellularis is available because few strains have been successfully isolated worldwide. In this study, a tissue culture system was used to determine the minimum inhibitory concentrations of both intracellular and extracellular activity against 10 Lawsonia isolates from the United States (n=6) and Europe (n=4). Results of these in vitro studies can be used as a basis for evaluating treatment options in the field. Use of a recombinant protein FliC for development of an indirect ELISA for the diagnosis of proliferative enteropathy. Serological tests are the most economical tools for diagnosis of proliferative enteropathy in pigs. This study, utilizing the flagellar protein, FliC, is the first report to illustrate the potential use of a recombinant protein of L. intracellularis in an indirect ELISA. Although the FliC-ELISA failed to demonstrate high DSn and low cross-reactivity, the advantage of this protein-based ELISA is that it required no culturing of live L. intracellularis for antigen preparation, therefore, enhancing the efficiency and ability to detect proliferative enteropathy worldwide. In vitro activity of chicken egg antibody (IgY) against L. intracellularis. Currently, methods to control proliferative enteropathy include long-term use of approved feed-grade antibiotics and vaccination. Furthermore, use of antimicrobial alternatives represents a more desirable management technique due to public health concerns over the potential antibiotic residues in meat and the risk of development of antibiotic resistance. In this study, Lawsonia-specific antibodies produced in chicken eggs were able to reduce the incidence of infection of cultured cells after challenge with L. intracellularis.
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IMPACT: 2002/10 TO 2007/09<BR>
Proliferative enteropathy is an important infectious disease caused by the obligate intracellular bacterium, Lawsonia intracellularis. Little is known of the pathogenic mechanisms for this organism. Furthermore, sensitive and specific methods for diagnosing proliferative enteropathy are not universally available. Characterization of the gene products from this organism will help to identify genes responsible for microbial virulence, or that will be useful in the development of diagnostic reagents and candidate recombinant vaccines against this organism. Development of a molecular typing database will enable further studies on the ecology and epidemiology of L. intracellularis.