Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

D. L. Harris


Lawsonia intracellularis, the causative agent of porcine proliferative enteropathy (PPE), is a major cause of economic losses in the swine industry. Lawsonia intracellularis is a grain negative, microaerophilic, obligately intracellular pathogen. The disease associated with L. intracellularis usually results in poor weight gains and increased time to market. Newer techniques for detecting L. intracellularis infections are now available which allow ante-mortem testing including polymerase chain reaction (PCR) of the feces and an indirect fluorescent antibody test;This dissertation describes the development of a live attenuated strain of L. intracellularis after continuous passage within suspended tissue cultures. This attenuated strain was shown to be safe at high doses in dexamethasone treated pigs as well as safe after repeated backpassage in pigs, demonstrating a failure to revert back to virulence. Also described in this dissertation are studies used to evaluate the attenuated strain of L. intracellularis in pigs vaccinated at three weeks, then challenged with a pure culture of virulent L. intracellularis. Lastly, experiments using tiamulin hydrogen fumarate (DenagardTM) are described for the control and prevention of PPE when administered in the feed or the drinking water as treatment post-infection. The use of biological, pharmaceutical, and updated managerial control measures will give swine producers more options for the control of PPE resulting in better performance and less cost to market.



Digital Repository @ Iowa State University,

Copyright Owner

Jeffrey Paul Knittel



Proquest ID


File Format


File Size

201 pages