Persistent Intestinal Colonisation and Systemic Immune Activation Following Experimental Campylobacter jejuni Infection in Broiler Chickens.

Campylobacteriosis is one of the leading foodborne bacterial illnesses worldwide, with poultry meat representing its principal source of human infection. Broiler chickens are a key reservoir for Campylobacter jejuni, where the bacterium persists in the gastrointestinal tract without disease. Understanding this host-pathogen interaction is essential to clarify mechanisms of persistence and food safety implications. This study investigated persistent C. jejuni colonisation and systemic immune responses in experimentally infected broiler chickens. Following oral challenge with the virulent ST-403 strain, animals were monitored under controlled conditions. Caecal bacterial loads were determined at 13, 27, 35 and 41 days post-infection, alongside serum total and antigen-specific IgY levels and circulating cytokines and chemokines using ELISA and multiplex assays. C. jejuni rapidly colonised the caecum and persisted throughout the study, although bacterial loads gradually declined over time but remained high. Total IgY increased early after infection and then stabilized. Antigen-specific antibodies were higher in infected chickens than in controls. Cytokine profiling revealed distinct temporal patterns, with increased IL-6 and MIP-1β, decreased IL-2 and MIP-3α, and persistently low IFN-γ levels. C. jejuni established stable intestinal colonisation with a detectable but non-clearing systemic immune response. These findings further support the role of broiler chickens as a persistent reservoir for human exposure to C. jejuni.