Parenteral application of live E. coli and Salmonella Typhimurium vaccines as a tool to improve immune response

Live Salmonella typhimurium (LVST) and E. coli (LVEC) vaccines have been widely used across the poultry industry as successful measures of controlling colibacillosis and salmonella, respectively. Both products are applied by mass administration, either by spray or water. This results in high mucosal exposure to the vaccine, which induces immunity mostly driven by cellular and IgA immunity. A sequence of challenge studies was conducted with the objective of evaluating if, when these vaccines are given parenterally, immunity would be enhanced when compared with the conventional route. Across studies, live bacterial vaccines were administered to SPF leghorns either alone or in combination with an inactivated Salmonella Enteritidis, Infectious Bronchitis, and Newcastle Disease vaccine between 10 and 12 weeks of age. Results from the LVST studies showed that LVST given parenterally induced greater Salmonella spp. load and prevalence reductions against Salmonella groups B, C, and D challenges. This effect was also reflected by improved serology GMT in the parenteral LVST treatments. Results from the LVEC trials showed that parenteral administration of the vaccine consistently gave the best protection results across various APEC O78 and O2 challenge loads. In addition, combining LVEC with the inactivated vaccine further improved colibacillosis protection and reduction of clinical signs when compared with LVEC given parenterally by itself. In conclusion, both LVST and LVEC, when given parenterally, have shown the potential to broaden and further enhance their cross-protective features.

Key Words: Parenteral, Live vaccines, Salmonella, E. coli, Immunology.