Three groups of 100 individually marked salmonella-free chickens were followed for a period of 53 wk. The chickens were infected as day olds by crop instillation of 108 colony-forming units: one group with Salmonella enteritidis and a second group with Salmonella typhimurium. A third group was kept uninfected as controls.
The groups were monitored bacteriologically by examination of cloacal swabs and organs and serologically by examination of serum and egg yolk by a lipopolysaccharide enzyme-linked immunosorbent assay throughout the period.
Within the first week, 100% of birds in both infected groups were excreting salmonella bacteria in the feces. However, the number of fecal excretors declined rapidly with time, down to 6% in 16 wk for S. typhimurium and down to a similar level within the first 8 wk for S. enteritidis. For the latter, relapses with up to 40% positive birds were observed at the onset of egg production. For both S. typhimurium and S. enteritidis, positive bacteriologic cultures were obtained by sampling from internal organs at the end of the experiment, more than 1 yr from the time of infection.
At the age of 6–7 wk, 50% of the chickens in the two infected groups showed a measurable serologic response in serum samples. The response persisted throughout the study in both serum and egg yolk samples.
The inclusion of serologic methods is a valuable additional tool in the detection of salmonella in poultry, but serology should be used in conjunction with bacteriologic methods in surveillance programs, in particular to detect flocks in early stages of infection before a measurable serologic response has been raised.