‘Competitive exclusion’ is potential benefit of live Salmonella vaccines in young birds
Live vaccines for Salmonella have been found to start offering protection within a few days of administration, acting “almost as a [form of] competitive exclusion,” said Chuck Hofacre, president of the Southern Poultry Research Group.
A normal antibody immune response would take 7 to 14 days, so something else is evidently occurring, Hofacre told Poultry Health Today.
“We also know [live vaccines] are quite effective against Salmonella groups B and D, including Enteritidis, Heidelberg or Typhimurium,” he added. “They’re not quite as effective against the group-C strains like Kentucky, but one study we’ve done has shown they are moderately protective against Salmonella Infantis, which is becoming more of a concern.”
Hofacre also said a live Salmonella vaccine can competitively exclude some dissimilar strains in young poultry.
“Broilers are really just young poultry,” he said. “We also use live vaccines in our breeders when they’re young.”
More pressure on processors
The USDA Food Safety and Inspection Service has put more pressure on processors to meet performance standards, Hofacre said.
“More companies have begun to use live vaccines because they are very easy, and they’ve been accepted around the world as a good intervention for rapidly lowering your risk for Salmonella, especially those at highest risk for human foodborne illness coming into the plant,” he added.
Importance of a booster
In the US, most of the live vaccines for Salmonella are labeled for boosting at 10 to 14 days of age, Hofacre said.
“We know that a boost can significantly improve our ability to reduce those human foodborne Salmonella,” he said. “If a company is really struggling with, say, Salmonella Enteritidis or Salmonella Typhimurium in their final product, a boost would be a good way to help reduce the risk of having those Salmonella coming in.”
Vaccination strategies for layers and breeders
With layers and breeders, Hofacre said producers should protect the pullet to avoid colonization with the Salmonella that can potentially create a human foodborne-illness problem.
“In those cases, we need to vaccinate as early as we can at 1 day of age and we need to boost as well,” he said. “Live Salmonella vaccines last about 4 to 6 weeks so we recommend boosting somewhere in that 4- to 6-week range. Then, depending on our killed-vaccination program, we may boost a third time at 8 to 10 weeks of age.
“The decision has to be economics,” Hofacre explained. “If you’re looking at it purely from a food-safety standpoint, then yes, it would be recommended to use both. If you factor in the economics, then you look at what Salmonella strains are coming through the processing plant that are showing up in the carcass rinses or the parts rinses.”
The live vaccines currently on the market provide good protection against group B serotypes and group D serotypes, Hofacre said. However, if more group C serotypes emerge, that could become an issue because current vaccines are not as protective against this group.
If that happens, “we’re going to need some new vaccines that give broader cross-protection than what we see with the current ones,” Hofacre said. “Research should be progressing in terms of vaccines that can give us greater cross-protection to more serotypes, particularly those that could cause human foodborne illness.”
Posted on June 2, 2022