Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Veterinary Microbiology and Preventive Medicine

First Advisor

D. L. Hank Harris


Human salmonellosis is considered one of the most important foodborne illnesses in the United States. While eggs are considered to be a major foodborne source of Salmonella, pork has been estimated to account for 6-9% of the cases in the U.S. The objectives of this work focused on the epidemiology and control of human foodborne Salmonella in finishing pigs. Study one was designed to estimate the prevalence of Salmonella in U.S. finishing pigs and also to characterize the diversity of isolates from the farms. Study two focused on eliminating or reducing the amount of Salmonella on one of the farms identified in Study one. Study three used two different farms from Study one in order to compare Salmonella isolated from pigs on the farm versus Salmonella isolated from cohort pigs at slaughter. Finally, Study four investigated the ability of Salmonella vaccines to eliminate or reduce acute Salmonella infection of pigs as described in Study three. In other words, can a Salmonella vaccine be a form of food safety intervention by protecting pigs from becoming infected between the farm and abattoir?;The results from this work indicate that continued monitoring of Salmonella in finishing pigs on US farms may not be necessary. A very small percentage had any significant level of Salmonella or clinical salmonellosis. In herds where Salmonella reduction is desired, prevalence can be significantly reduced in finishing pigs in farms being depopulated-repopulated due to other pathogens such as porcine reproductive and respiratory virus (PRRSV) and Mycoplasma hyopneumoniae. Results from this work indicate that pigs at the abattoir contain different serovars and subtypes of serovars not present on the source farm. Thus regardless of the on-farm Salmonella status of the pigs, acute infection during transport and lairage may have more of an influence on the prevalence of Salmonella in pigs at slaughter. It seems that vaccination is not the answer for protecting pigs from this acute infection just prior to slaughter. Future work to control this infection should focus solely on decontamination of all points between the farm and the rail including trucks, trading stations, loading docks, and lairage pens.



Digital Repository @ Iowa State University,

Copyright Owner

Matthew Michael Erdman



Proquest ID


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File Size

146 pages