Comparative dynamics of salmonella infection after primary and secondary challenge of mice exposed to 10 and 23 C.

Mortality of mice increased significantly as a result of cold exposure when the animals were challenged orally with Salmonella typhimurium, strain RIA. As reported earlier, cold exposure alone did not kill control animals nor did oral challenge at room temperature. No differences were apparent in the number of Salmonella per gram of liver-spleen, colon, or lung between groups of infected mice housed at 23 and 10 C. The number of bacteria increased equally in liver-spleen samples during the period of increasing mortality in the group housed at 10 C and the period of overt illness in those housed at 23 C. The ability to clear the bloodstream of a secondary intravenous challenge did not seem to be impaired by cold exposure. The bacterial load in the spleen and the rate of change in weight of that organ was equal in animals given a secondary challenge at 10 or 23 C. However, the absolute spleen weight was less in the cold-exposed group as was survival when the secondary challenge was administered 3 days after the primary oral challenge. The studies indicate that endotoxin from S. typhimurium may sensitize mice to the lethal effects of cold exposure. The increase in mortality observed in cold-exposed, infected mice is not due to greater bacterial proliferation in these animals. Rather, the combined stress effects of the bacterial agent(s) and cold may link lympholytic effects to impaired detoxification and increased energy demands, which often leads to lethal vascular collapse in cold-exposed, infected mice.