Observations on the persistence and vertical transmission of Salmonella enterica serovars Pullorum and Gallinarum in chickens: effect of bacterial and host genetic background

Commercial laying hens inoculated with a strain of Salmonella enterica ser. Pullorum when they were 4 days old showed no morbidity, but harboured infe ction until they came into lay, and then produced S. Pullorum-contaminated eggs and infected progeny. There was limited evidence of transmission of ma ternal immunity to the progeny. Attempts were made to set up similar infect ions in hens with Salmonella Gallinarum, but without success. Infection eit her resulted in clinical disease or elimination of the pathogen. Infection of birds when in lay produced a similar result. The possibility of eggs bec oming contaminated with S. Gallinarum after they were laid in the nest box was evaluated but there was no evidence for this. In-bred chicken lines wit h a SalI-susceptible phenotype showed greater localization of S. Pullorum i n the reproductive tract than did a SalI-resistant line. In addition, in-br ed birds, which were SalI resistant but showed greater susceptibility to in testinal colonization by Salmonella, infected with S. Gallinarum when they were 1 week old, showed longer term persistence in the liver and spleen tha n did a resistant line.