A vaccination programme combining a live attenuated Salmonella Typhimurium and an autogenous inactivated Salmonella Enteritidis vaccine confers protection and reduces ovarian colonisation with the Salmonella Enteritidis isolate 7A, PT12.

Salmonella enterica serovar Enteritidis (SE) can colonise chicken ovaries and contaminate eggs, posing a global risk of human gastroenteritis, often linked to raw or undercooked eggs. Control options for SE outbreaks in Australia are limited; autogenous SE vaccines are commonly used, while live attenuated Salmonella Typhimurium (ST) vaccines are available. One such vaccine, has been registered in Australia since 1996. This study evaluated three vaccination programmes in laying hens: a live ST vaccine, an autogenous SE vaccine and a combination of both against challenge with an Australian SE isolate (strain 7A). Hens were vaccinated on commercial farms, then challenged orally at 17 weeks. Serological responses for serotypes B and D were monitored at 11 and 16 weeks. Cloacal swabs assessed SE shedding at 3, 7, 14, 21 and 28 days post challenge (DPC). At 32 DPC, hens were euthanased, and ovaries and caeca cultured for Salmonella. Results showed that priming with a live ST vaccine followed by a killed SE vaccine provided strong protection, particularly against ovarian colonisation. In contrast, the autogenous SE vaccine alone did not sufficiently protect ovarian tissue. These findings indicate that priming with a live ST vaccine is essential before administering an inactivated SE vaccine to reduce ovarian colonisation and SE shedding in eggs, ultimately lowering SE-related enteritis in humans.