NEW ORLEANS Contamination by the bacterium Campylobacter may be reduced by administering vaccine to poultry on the farm, holding out the promise of a significant step in the public health effort to combat human gastroenteritis infection at the source, according to the results presented here recently.
The vaccination resulted in a 16% to 93% reduction in the numbers of bacteria, specifically Campylobacter jejuni carried by broiler chickens, according to Brandt E. Rice, a PhD candidate in the microbiology department of the University of Maryland at College Park. Rice conducted the testing of the vaccine in poultry under the guidance of David M. Rollins, PhD, of the Naval Research Institute, Bethesda, Md., and Sam W. Joseph, PhD, of the University of Maryland at College Park.
A vaccine approach has significant implications for improving public health, said Rice, who works in the Naval Medical Research Institute. High levels of Campylobacter bacteria in live chickens result in widespread cross-contamination of retail poultry products during high-speed, mechanized processing operations, according to Rice, who presented the data at the 96th General Meeting of the American Society for Microbiology.
"The results of our vaccine studies are promising and suggest that further levels of colonization reduction of Campylobacter in poultry are possible," said Rice, who noted that with the planned revamping of the federal meat inspection system that was recently announced, there will be a greater interest on the part of poultry producers in investigating a regimen that vaccinates birds during the production stage. This is the first report of such a vaccine regimen in poultry.
It is still not known for certain how flocks of poultry are contaminated by the Campylobacter bacteria. "Unlike infection in humans, poultry appear to be a natural host for these bacteria and broiler chickens regularly harbor significant numbers of Campylobacter with no apparent detrimental effects on the health of the bird," Rice said. "Neither the nature of this association between the bacteria and the chicken, nor the source of commercial poultry flock contamination, have been specifically identified."
Rice said experts have speculated that the bacteria could be carried by insects or rodents, or transmitted through a water source. "The lack of such basic knowledge has impeded efforts to eliminate contamination of poultry flocks by Campylobacter," he said.
What is known, however, is that the bacterium is easily spread to an uncontaminated poultry flock by infected birds. At present, the most effective means of combating C. jejuni contamination is while preparing the food. Attempts to control this contamination during processing have met with limited success.
C. jejuni is one of the leading causes of human gastroenteritis, with estimated population infection rates of 1% to 2% annually in both the United States and England. In the United States alone, about 2.4 million people are infected annually, according to current estimates. Between 40% to 70% of human infections are associated with the mishandling or consumption of undercooked retail poultry, where levels of contamination can be as high as 83%.
"The severity of illness associated with Campylobacter infection is variable, typically causing diarrhea with abdominal cramps, malaise, nausea and vomiting lasting two to seven days," Rice said. "However, more severe dysentery-like illness can occur, followed by relapses analogous to ulcerative colitis, and occasionally serious arthritic and neurologic complications are observed.
"It is anticipated that the administration of this vaccine in humans will enhance the body's immune response against Campylobacter and thus, prevent disease. Specifically, any such vaccine should impart its effect at the mucosal surfaces of the gastrointestinal [GI] tract where increases in anti-Campylobacter antibodies would be the most effective in preventing these pathogens from becoming established and causing disease," Rice said.
In the study, three vaccine trials were performed with various levels of doses and timings. The poultry vaccinations consisted of two to three doses of vaccine administered either orally or rectally. The use of an oral vaccine may ultimately allow for the introduction of the vaccine into the water supply, thus facilitating the ability of poultry producers to vaccinate their flocks. The vaccine was composed of a liquid suspension of Campylobacter cells that had been killed by treatment with formaldehyde. This process leaves the cells intact, enabling the chicken to elicit an immune response anticipated to be similar to that directed against the live bacterium. "In this form," said Rice, "the cells are unable to multiply or transmit infection to humans."
To improve on the 16% to 93% reduction in the total amount of Campylobacter achieved in the vaccinated chickens, a component to further stimulate the immune response, known as adjuvant, was incorporated into the vaccine. The heat labile toxin of another bacterium, Escherichia coli was used as the adjuvant. This modification resulted in a further increase in the mucosal immune response of the rectally vaccinated chickens, but did not further improve their resistance to colonization by Campylobacter.
The effectiveness of the vaccine was measured by challenging the vaccinated birds with live Campylobacter and comparing the numbers of these bacteria that colonize the gastrointestinal tract of the chickens to the numbers colonizing non-vaccinated birds. In addition, the immune response in vaccinated and non-vaccinated birds was compared.
The anti-Campylobacter vaccine was initially conceived for human use and developed in the Enteric Diseases Program of the Naval Medical Research Institute. A slightly modified version of this vaccine, produced in collaboration with Microcarb Inc. of Gaithersburg, Md., is currently undergoing Phase 1 human clinical trials.
For more information:
- Rice BE, Rollins DM, Mallinson ET, et al. Efficacy of a mucosal anti-Campylobacter jejuni vaccine administered with and without Escherichia coli heat labile toxin in 1 day- to 2-week-old commercial broiler chickens. Abstract E-30. Presented at the 96th General Meeting of the American Society for Microbiology, New Orleans, May 19-23.
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