Hyporesponsiveness of the systemic and mucosal humoral immune systems in chickens infected with Salmonella enterica serovar enteritidis at one day of age

Newly hatched chicks lack immunological maturity, which could compromise their ability to respond to infection by pathogens such as Salmonella enterica serovar enteritidis (S. enteritidis; SE). A study was conducted in which chicks were infected with a sublethal dose of SE at 1 d posthatch, and the systemic and intestinal immune responses to the challenge were followed over time. Birds infected at this age experienced difficulty in clearing the infection, and 50% of the individual birds remained persistently infected until 23 wk of age. These birds exhibited only a marginal systemic and mucosal humoral immune response to the infection. No response or little response was observed 1 wk postchallenge; responses increased somewhat over time. On many of the sampling times, 50% or more of the culture-positive birds lacked a detectable plasma or intestinal response. Levels of 10³ to 10⁵ SE/g of feces could be found in the intestines of birds eliciting a good IgA response, indicating that, when these birds did respond mucosally, the IgA produced was incapable of clearing the organism once the infection was established. Birds infected during this time also experienced reduced ability to respond to vaccination. Compared with uninfected controls, depressed responsiveness to an S. enteritidis bacterin was observed in infected birds 1 and 2 wk after administration, whereas those individuals receiving an inactivated Newcastle disease vaccine (NDV) experienced a reduced response 4 and 6 wk postvaccination, indicating that the persistent infection affected the ability of the immune system to respond to homologous and heterologous antigens. These results demonstrate that exposure of chickens to SE early in life interferes with the ability of these individuals to respond humorally to the infection and to other antigenic stimuli; such effects can be observed for at least 23 wk.