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 infection until they came into lay, and then produced S. Pullorum-contaminated eggs and infected progeny. There was limited evidence of transmission of maternal immunity to the progeny. Attempts were made to set up similar infections in hens with Salmonella Gallinarum, but without success. Infection either resulted in clinical disease or elimination of the pathogen. Infection of birds when in lay produced a similar result. The possibility of eggs becoming 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 with a SalI-susceptible phenotype showed greater localization of S. Pullorum in the reproductive tract than did a SalI-resistant line. In addition, in-bred birds, which were SalI resistant but showed greater susceptibility to intestinal colonization by Salmonella, infected with S. Gallinarum when they were 1 week old, showed longer term persistence in the liver and spleen than did a resistant line.