Abstract
BackgroundCampylobacter jejuni is a leading bacterial cause of food-borne illness in humans. Symptoms range from mild gastroenteritis to dysentery. Contaminated chicken meat is the most common cause of infection. Broiler chickens become colonized with high numbers of C. jejuni in the intestinal tract, but do not become clinically ill. Vaccination of broiler chicks to control colonization by C. jejuni is challenging because immune function is limited in the first 2 weeks post-hatch and immune suppressive maternal antibodies are common. In addition, there is little time for induction of immunity, since broilers reach slaughter weight by 5–6 weeks of age. In the current study the immunogenicity of a C. jejuni capsular polysaccharide—diphtheria toxoid conjugated vaccine (CPSconj), administered subcutaneously with various adjuvants was assessed and the efficacy of vaccination for reducing cecal colonization after experimental challenge was evaluated by determining colony-forming units (CFU) of C. jejuni in cecal contents.ResultsThe CPSconj vaccine was immunogenic when administered as three doses at 3, 4 and 5 weeks of age to specific pathogen free chicks lacking maternal antibodies (seroconversion rates up to 75%). Commercial broiler chicks (having maternal antibodies) receiving two doses of CPSconj vaccine at 7 and 21 days of age did not seroconvert before oral challenge at 29 days, but 33% seroconverted post challenge; none of the placebo-injected, challenged birds seroconverted. Vaccinated birds had significantly lower numbers of C. jejuni in cecal contents than control birds at necropsy (38 days of age). CFU of C. jejuni did not differ significantly among groups of birds receiving CPSconj vaccine with different adjuvants. In two trials, the mean reduction in CFU associated with vaccination was 0.64 log10 units.ConclusionsThe CPSconj vaccine was immunogenic in chicks lacking maternal antibodies, vaccinated beginning at 3 weeks of age. In commercial broiler birds (possessing maternal antibodies) vaccinated at 7 and 21 days of age, 33% of birds seroconverted by 9 days after challenge, and there was a modest, but significant, reduction in cecal counts of C. jejuni. Further studies are needed to optimize adjuvant, route of delivery and scheduling of administration of this vaccine.
Highlights
Campylobacter jejuni is a leading bacterial cause of food-borne illness in humans
Immunogenicity of the CPS conjugate vaccine in the absence of maternal antibodies Mean serum IgG antibody titres increased in vaccinated specific pathogen free (SPF) birds, but not in negative control birds that received phosphate buffered saline (PBS) (Figure 1)
Seroconversion rates were 20, 40 and 75% by 6 weeks of age in birds receiving two doses of capsular polysaccharide—diphtheria toxoid conjugated vaccine (CPSconj) vaccine with CpG, two doses CPSconj with Quil A and three doses CPSconj with Quil A respectively
Summary
Campylobacter jejuni is a leading bacterial cause of food-borne illness in humans. Broiler chickens become colonized with high numbers of C. jejuni in the intestinal tract, but do not become clinically ill. Vaccination of broiler chicks to control colonization by C. jejuni is challenging because immune function is limited in the first 2 weeks post-hatch and immune suppressive maternal antibodies are common. Enhanced biosecurity in poultry flocks and improved hygiene during processing of poultry products have potential to reduce contamination of meat at the retail level, but vaccination of broiler chickens will be needed in conjunction with these approaches to have a major impact on campylobacteriosis in humans [7]. Putative virulence factors and potential vaccine antigens have included outer membrane proteins [8], flagellin [11, 16], and transport proteins [12,13,14]
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