Salmonella Typhi Infection Severity

Typhoid fever caused by Salmonella Typhi infection can occur in endemic or epidemic forms in human populations, following oral ingestion of these bacteria. When chimpanzees were experimentally given this organism, they required larger doses to obtain an infection and had a reduced severity of the symptoms and pathological responses. The disease in adult chimpanzees was said to closely resemble the mild form of human typhoid fever frequently seen in human children. The complicated and sometimes lethal form of the disease seen in human adults was not seen in the chimpanzee. The reason for this difference is unclear, but it may be that an over-reactive human immune response is responsible for some of the most severe symptoms.