This summer's nationwide Salmonella outbreak and related egg recall are likely drivers of a recent rise in the use of Salmonella enteritidis vaccines.
Gary Baxter, marketing director for CEVA Biomune, which produces poultry-use Salmonella vaccines, said market research indicates about 60 percent of egg producers were vaccinating their flocks against S enteritidis at the end of 2009, but he estimated about 78 or 79 percent of producers were vaccinating by November 2010. At least 15 percent of the industry diverts all its eggs for pasteurization, and he expects industry members are close to universally adopting vaccination.
While vaccine use has increased in each of the past five years, Baxter said the recent illnesses and new Food and Drug Administration regulations related to microbial testing and control were both likely causes of the substantial jump in flock vaccination rates. He said his company produces most of the nation's poultry-use S enteritidis vaccine.
Two Iowa-based egg producers, Wright County Egg and Hillandale Farms of Iowa Inc., issued nationwide recalls for more than 500 million eggs after investigations by state and federal health officials indicated the two farms were likely the source of shell eggs connected with more than 1,800 illnesses nationwide during the outbreak, according to information from the Centers for Disease Control and Prevention and the FDA.
About one year prior to the outbreak's peak, the FDA had announced new rules intended to reduce Salmonella-related illnesses. The rules took effect July 9 and include requirements that egg producers have written S enteritidis prevention plans and conduct contamination tests.
Coinciding influences on vaccine use
Dr. David J. Henzler, a consultant for the poultry industry, said veterinarians and egg producers have successfully used vaccines to reduce Salmonella shedding, particularly when the vaccines were administered prior to molting and used along with prevention methods such as effective rodent control and screening of the chicks and pullets entering flocks. While the FDA regulations that took effect in July 2010 could additionally reduce the risk of Salmonella outbreaks, he does not think the changes were in place and enforced quickly enough to prevent the summer outbreak.
Dr. Henzler said he has worked with both companies involved in the recall, but he was not familiar with their vaccine programs. However, he said egg industry members individually decide which methods are worth their costs, and he noted that publicly traded egg-producing companies are particularly aware of the risks posed by foodborne illness outbreaks.
Dr. Darrell Trampel, an extension poultry veterinarian and poultry diagnostician in the Iowa State University College of Veterinary Medicine, thinks the 2010 Salmonella outbreak served as a wake-up call for the egg industry.
"I think the long-term effect of this outbreak is going to be a safer egg supply," Dr. Trampel said.
Some producers who vaccinate their chickens administer live vaccines consisting of gene-deleted attenuated S enterica serovar Typhimurium within the first few days after hatching and again when the chickens are about four weeks old. Live vaccines can be administered along with, or instead of, vaccines that contain killed S enteritidis bacteria; the killed vaccines are usually given when the chickens are between 13 and 15 weeks old.
"Vaccination is not 100 percent effective, but it is a very useful tool to control Salmonella enteritidis in chickens," Dr. Trampel said. "It's important, and my recommendation is that all egg producers use both live and killed vaccines."
Dr. Charles L. Hofacre, secretary and treasurer for the American Association of Avian Pathologists, also recommended use of both attenuated live and inactivated vaccines.
He said vaccination was also increasing in the broiler industry, but vaccination rates remained higher in the egg industry. In addition to vaccination, producers should also implement rodent control, insect control, and biosecurity measures to reduce contamination, he said.
While vaccination can involve a substantial investment, particularly among large-scale egg producers, Dr. Hofacre thinks many producers want the economic fairness that would come from a requirement that all hens be vaccinated. He estimates that it costs producers about 18 cents to vaccinate each hen, and producers do not benefit directly from that "insurance policy" as they do with use of vaccines that improve hen health.
However, with the increased use of S enteritidis vaccines and other control measures, Dr. Hofacre expects a reduction in foodborne illnesses and outbreaks and increased consumer confidence.
Voluntary action with encouragement
Gene Gregory, president and CEO of United Egg Producers, said his organization has twice in the past six years urged FDA officials to provide incentives for vaccine use.
"We believe vaccines are an important component of food safety programs," Gregory said.
In a Sept. 10 letter to the FDA, Gregory indicated that the UEP supports FDA regulations intended to prevent S enteritidis contamination in eggs, but the organization thinks it is imperative to take additional steps to further reduce the risk of contamination and strengthen public confidence in regulators and producers.
"Therefore, we respectfully urge the FDA to make SE vaccination an integral part of producer compliance with your regulations, and to do so in a manner that will ensure universal adoption of vaccination programs," the letter states.
The letter states that experiences of members who have implemented vaccination programs and colleagues in the United Kingdom, "where such programs are effectively mandatory," have led the UEP to conclude that it is important to vaccinate all hens.
Gregory's letter advocates that the FDA amend its S enteritidis guidance document to state that all producers should add vaccination to their plans, which will avoid delays under the regulatory process and influence nearly all producers who are not currently vaccinating hens to adopt vaccination programs.
Gregory said in a message that, out of consideration for small-scale egg producers, his organization did not ask for mandatory vaccination. The FDA considered requiring use of S enteritidis vaccines as part of a proposed egg safety rule issued in 2004, but agency officials determined that they did not have enough evidence to add such a requirement. But FDA officials said in late August they were working with the Department of Agriculture to review data on Salmonella vaccines and "determine whether additional recommendations or requirements are appropriate."
Gerardo A. Ramirez, PhD, a consumer safety officer with the FDA Center for Food Safety and Applied Nutrition, is examining the effectiveness and availability of poultry-use vaccines. He said that, when the 2004 egg safety rule was drafted, the agency particularly wanted more evidence from studies involving real-world settings as opposed to laboratory conditions. The FDA is reexamining the issue and could make decisions ranging from upholding existing regulations and guidance without changes to requiring vaccine use.
However, Dr. Ramirez stressed that the agency has not made any decisions and is considering all scientific evidence and literature located so far while searching for additional evidence. Agency spokeswoman Laura Alvey added that the FDA would seek public comments if any changes were proposed.
Dr. Ramirez said his research has shown a broad range of efficacy across vaccine applications. Effective vaccines could be one part of Salmonella control, but he hopes nobody mistakenly believes vaccination could replace biosecurity, pest control, and disinfection practices.
Cindy Ragin, a spokeswoman for the USDA Animal and Plant Health Inspection Service, said the USDA's S enteritidis working group was evaluating the efficacy of vaccines in determining whether to recommend that the FDA require vaccination. The department has provided data to the FDA, and APHIS' evaluation was ongoing.