Date of Graduation

8-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level

Graduate

Department

Poultry Science

Advisor

Guillermo Tellez

Committee Member

Billy M. Hargis

Second Committee Member

Neil R. Pumford

Third Committee Member

Lisa R. Bielke

Fourth Committee Member

Luc R. Berghman

Abstract

The following studies evaluated our hypothesis that transmission by the fecal-respiratory route may be a viable portal of entry for Salmonella and could explain some clinical impressions of relatively low-dose infectivity under field conditions in relation to the requisite high oral challenge dose that is typically required for infection of poultry through the oral route in laboratory studies. Initial field reports indicating tracheal sampling to be a sensitive tool for monitoring Salmonella infection in commercial flocks, suggested that tracheal contamination could be a good indicator of Salmonella infection under commercial conditions. Further, a usual assumption regarding airborne Salmonella reaching the upper respiratory tract, would ultimately involve oral ingestion, due to the presence of the mucociliary clearance was evaluated. Suspension in 1% mucin failed to increase the infectivity at any dose of Salmonella when compared to OR administration without mucin and intratracheal (IT) challenge, which was also recovered from lung tissue. IT administration was more effective or at least as effective at colonizing the ceca of 7d chickens, suggesting that the respiratory tract may be an overlooked potential portal of entry for Salmonellae. Finally, the hypothesis was evaluated through IT administration of Salmonella, in comparison with oral administration. A significantly higher or equivalent cecal recovery of Salmonella, with a clear dose response curve, with the IT groups as compared to groups challenged OR, added further support to the hypothesis. Both the cecal CFU recovery data and organ invasion incidence data from these experiments provided evidence for the subsequent fate of Salmonella exposed to the respiratory system, potentially involving a systemic route. Overall, our data suggests that the respiratory route might be a viable portal of entry for Salmonella in poultry. Clarification of the potential importance of the respiratory tract for Salmonella transmission under field conditions may be of critical importance as efforts to develop intervention strategies to reduce transmission of these pathogens in poultry continue.

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