Observations on the pathogenesis of experimental Salmonella typhimurium infection in chickens.

The virulence of Salmonella typhimurium strains for day-old chickens was examined. The mortality following oral inoculation varied from 0 to 100 per cent. Some breeds were more susceptible than others. There was no correlation between oral and parenteral virulence. Pathogenesis studies associated with one of the most virulent strains suggested that, after invasion, organisms multiplied in the liver and spleen and spread to other organs producing a systemic infection. The cause of death was probably a combination of anorexia and dehydration resulting from general malaise and diarrhoea. A virulent strain studied in detail spread through the body faster, persisted for a longer period and was more invasive than an avirulent strain. In the system studied invasiveness was the virulence determinant of overriding importance.