Experimental infection of laying hens with Campylobacter coli and Campylobacter jejuni: Shedding dynamics and internal organ colonization.

Campylobacteriosis is considered the most common foodborne bacterial zoonosis worldwide. The species most frequently associated with enteric cases in humans is Campylobacter jejuni, followed by C. coli, and they can be transmitted through poultry meat. This study aimed to evaluate the dynamics of fecal shedding and the ability of these pathogens to colonize internal organs in laying hens using an experimental infection model. Two independent trials were conducted using sixteen-week-old laying hens, orally infected with 1 × 10 ³ CFU or 1 × 10 ¹ ⁰ CFU of C. jejuni or C. coli. Cloacal swabs were collected daily up to 11 days post-infection (dpi) to assess bacterial shedding. At 4 and 11 dpi, subsets of birds were euthanized for bacteriological analysis of cecal contents and internal organs (liver, spleen, gallbladder, and ovarian follicles), as well as for serological and histopathological evaluation. Both Campylobacter species rapidly colonized the birds, with all animals becoming positive by 4-9 dpi regardless of the infective dose. Although earlier detection was observed in the high-dose groups, no significant differences were found in cecal bacterial loads between treatments. Notably, Campylobacter was isolated from internal organs, including ovarian follicles, as early as 4 dpi, demonstrating its ability to disseminate beyond the intestinal tract. Despite systemic distribution, no clinical signs or histopathological lesions were observed, confirming the asymptomatic carrier status of infected birds. In conclusion, both C. jejuni and C. coli efficiently colonize laying hens and can disseminate to extraintestinal sites, including reproductive tissues. While these findings support the biological plausibility of vertical transmission, its epidemiological relevance appears limited, with horizontal transmission remaining the predominant route in poultry production.