Direct Manipulation of Corticotropin Releasing Factor to Identify the Relationship Between Stress and Pathogen Shedding in Pigs

NON-TECHNICAL SUMMARY: Management practices such as transportation, weaning, handling and the formation of new groups of animals are stressful to pigs. Stress from management practices been has also been indirectly linked to an increase in the shedding of pathogens. By combining a defined stress model with defined pathogen challenge models we will isolate the stress response and be able to determine if there is indeed a pathogen shedding response. The information obtained from this project will provide a much needed fundamental understanding of the mechanism by which stress induces changes in epizootic pathogen shedding.
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APPROACH:
<ol><li>Using biocontainment chambers, to prevent cross contamination between individual animals and contain pathogens used in the experiment, develop stable populations of experimental animals (piglets) and profile their baseline immune and microbial parameters.
<li>Evaluate the effects of stress on pathogen shedding in pigs by comparing test animal groups that are exposed to stress (CRF) and Salmonella enterica as compared to control groups exposed only to a Salmonella enterica.
<li>Evaluate the effects of Astressin on pigs using test animal populations exposed to S. enterica and Astressin as compared to control groups exposed to S. enterica but not Astressin.
<li>Evaluate the effects of combining CRF and Astressin on test animal populations exposed to S. enterica as compared to control groups exposed to S. enterica and CRF only. </ol>

PROGRESS: 2002/09 TO 2005/08<BR>
Epizootic pathogens in human food continue to be traced to food-producing animals. In swine, these include toxigenic E.coli and Salmonella species. What has been established is that management practices (mixing, handling, transport) can be stressful. Stress has been associated with pathogen shedding in the live animal. Corticotrophin Releasing Hormone (CRH) is released in the brain in response to stress. The hypothesis is that CRH induced stress response could regulate an animals immune system, resulting in increased pathogen shedding in pigs. For the CRH stress model we surgically implanted an intracerebroventricular cannula and infused pigs (weaned pigs ~10 kg body weight) with CRH (n=13) using a microosmotic pump that delivered 10 microliters/hour of CRH (0.5 mg/ml solution) or saline (n = 13) over 3 days. At time 0, just before CRH infusion began, we infected the animals with Salmonella typhimurium at 5 x 109 CFU by oral bolus. Feces were collected for analysis of S. typhimurium concentrations every 12 hours. Statistics were performed by ANOVA with times as the dependent variable split by treatment. Based upon analysis of shedding over time it was found that there was no significant difference in shedding between the treatment and controls (infused with saline) in the first 60 hours after infection. However after the initial 60 hours the treatment animals (those given CRH) had significantly lower shedding of the Salmonella spp. The P-values for the time periods are shown in the following table. Thus, it seems that low level chronic stress response induced by this concentration of CRH may promote a more rapid clearance of Salmonella spp. from the intestine over time. These results would seem to indicate that the type of stress induced by CRH infusion might reduce pathogen shedding after 60 hours. The design of management practices to take advantage of this Salmonella specific phenomenon will be an interesting direction of future research. Table 1. Statistics of Salmonella shedding over time. Time (hr)24 36 48 60 72 84 P value .465 .499 .572 .842 .034 .028 Evaluation of Escherichia coli shedding in pigs using the above model revealed a significant rise in shedding between 12 and 72 hours after induction of stress with CRH. Following this initial period the levels of E. coli shedding normalized among both treatments (control and CRH). This indicates that a different mechanism may be involved in the responses of Salmonella and E. coli in relation to CRH induced stress. It appears that Salmonella numbers shed in feces do not notably increase however E. coli numbers in feces do increase significantly. E. coli is typically noted as a non-invasive pathogen while Salmonella is invasive. Thus, we might be noting that the lowering of the immune response due to stress causes Salmonella to become more invasive thereby reducing their numbers being shed in feces while E. coli is non-invasive and their noted propogation in response to stress indicates that they also have obtained benefit from the animals stress response. Table 2. Statistics of E. coli shedding over time. Time (hr)12 24 36 48 60 72 P value .09 .05 .05 .06 .03 .03
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IMPACT: 2002/09 TO 2005/08<BR>
Safety of animal food products is of paramount importance to the consumer. Meat, in particular, has received criticism because of bacterial contamination. The Centers for Disease Control estimate that each year 76 million people contract a foodborne illness, resulting in as many as 325,000 hospitalizations and 9,000 deaths. It has also been estimated that medical costs and productivity losses for seven specific pathogens in food range between $6.5 billion and $34.9 billion annually. To take an informed approach toward enhancing the safety of our food supply at the farm level it is clear that we must: 1) identify the biological consequences of animal stress on pathogen shedding and 2) identify management practices and environments for cattle and swine that reduce pathogen loads in the animals and their environments.