Immunisation of chickens to reduce intestinal colonisation with Campylobacter jejuni

Nigella sativa-chitosan nanoparticles: Novel intestinal mucosal immunomodulator controls and protects against Salmonella enterica serovar Enteritidis infection in broilers

BACKGROUND

Salmonella Enteritidis (SE) propagates in chickens' gastrointestinal surfaces and is transmitted to humans, causing food poisoning. Oral supplementation with natural nanoparticles can overcome the harsh gastrointestinal conditions facing oral vaccines and requires no antibiotic administration to protect against microbial infection. This study was designed to study Nigella sativa-chitosan nanoparticles (CNP-NS) prophylactic immunomodulatory efficacy against SE infection in broiler chicks. The CNP-NS was prepared and characterized, and its in vivo immunomodulatory activities against an avian virulent-MDR SE-induced challenge in chicks were investigated.

RESULT

To verify the immune-protective activities of the CNP-NS, colony forming units (CFU) in the liver and fecal droppings; intestinal histopathological alterations and immune cell recruitment; MUC-2, TLR-4, cecal cytokines, and specific IgA gene expression levels were assessed. On the 7th and 12th days after the SE challenge, the CNP-NS supplemented chicks showed complete clearance of SE CFU in livers and fecal droppings, as well as an improvement in food conversion rate compared to non-supplemented CNP-NS that revealed the presence of the challenge SE CFU on the same days. A prominent influx of antigen presenting cells and lymphoid aggregates into the intestinal wall, spleen, and liver was detected with improvements in the intestinal villi morphometry of the CNP-NS-supplemented chicks. The changes of INF-γ, IL-1β, and IL-4 cecal cytokines, as well as TLR-4, MUC-2, and IgA mRNA expression levels, confirm CNP-NS immunomodulatory activities and provide a mechanism(s) for its protective actions against the induced SE challenge of the tested chickens.

CONCLUSION

These findings suggest promising useful insights into CNP-NS supplementation as a safe food additive for poultry meat consumers' and a protective immunomodulator of the chickens' mucosal immune systems. It could be recommended for epidemiological purposes to reduce the risk of SE food poisoning and transmission to humans.

The Data Behind Risk Analysis of Campylobacter Jejuni and Campylobacter Coli Infections

Campylobacter jejuni and Campylobacter coli are major causes of food-borne enteritis in humans. Poultry meat is known to be responsible for a large proportion of cases of human campylobacteriosis. However, other food-borne, environmental and animal sources are frequently associated with the disease in humans as well. Human campylobacteriosis causes gastroenteritis that in most cases is self-limiting. Nevertheless, the burden of the disease is relatively large compared with other food-borne diseases, which is mostly due to rare but long-lasting symptoms related to immunological sequelae. In order to pave the way to improved surveillance and control of human campylobacteriosis, we review here the data that is typically used for risk analysis to quantify the risk and disease burden, identify specific surveillance strategies and assist in choosing the most effective control strategies. Such data are mostly collected from the literature, and their nature is discussed here, for each of the three processes that are essential for a complete risk analysis procedure: risk assessment, risk management and risk communication. Of these, the first, risk assessment, is most dependent on data, and this process is subdivided into the steps of hazard identification, hazard characterization, exposure assessment and risk characterization. For each of these steps of risk assessment, information from published material that is typically collected will be summarized here. In addition, surveillance data are highly valuable for risk assessments. Different surveillance systems are employed in different countries, which can make international comparison of data challenging. Risk analysis typically results in targeted control strategies, and these again differ between countries. The applied control strategies are as yet not sufficient to eradicate human campylobacteriosis. The surveillance tools of Campylobacter in humans and exposure sources in place in different countries are briefly reviewed to better understand the Campylobacter dynamics and guide control strategies. Finally, the available control measures on different risk factors and exposure sources are presented.

On farm interventions to minimise Campylobacter spp. contamination in chicken

1. This review explores current and proposed on-farm interventions and assess the potential of these interventions against Campylobacter spp. 2. Interventions such as vaccination, feed/water-additives and, most importantly, consistent biosecurity, exhibit potential for the effective control of this pathogen and its dissemination within the food chain. 3. Due to the extensive diversity in the Campylobacter spp. genome and surface-expressed proteins, vaccination of poultry is not yet regarded as a completely effective strategy. 4. The acidification of drinking water through the addition of organic acids has been reported to decrease the risk of Campylobacter spp. colonisation in broiler flocks. Whilst this treatment alone will not completely protect birds, use of water acidification in combination with in-feed measures to further reduce the level of Campylobacter spp. colonisation in poultry may be an option meriting further exploration. 5. The use of varied types of feed supplements to reduce the intestinal population and shedding rate of Campylobacter spp. in poultry is an area of growing interest in the poultry industry. Such supplements include pro - and pre-biotics, organic acids, bacteriocins and bacteriophage, which may be added to feed and water. 6. From the literature, it is clear that a distinct, albeit not unexpected, difference between the performance of in-feed interventions exists when examined in vitro compared to those determined in in vivo studies. It is much more likely that pooling some of the discussed approaches in the in-feed tool kit will provide an answer. 7. Whilst on-farm biosecurity is essential to maintain a healthy flock and reduce disease transmission, even the most stringent biosecurity measures may not have sufficient, consistent and predictable effects in controlling Campylobacter spp. Furthermore, the combination of varied dietary approaches and improved biosecurity measures may synergistically improve control.

Survey of the U.S. Broiler Industry Regarding Pre- and Postharvest Interventions Targeted To Mitigate Campylobacter Contamination on Broiler Chicken Products

ABSTRACT

Campylobacter is one of the most commonly reported foodborne pathogens in the United States. Because poultry is considered a major source of Campylobacter infections in humans, reduction of Campylobacter contamination in poultry products is likely the most important and effective public health strategy for reducing the burden of campylobacteriosis in humans. A comprehensive on-line survey was conducted of key stakeholders in the U.S. broiler industry, including broiler farm managers (n = 18), poultry veterinarians (n = 18), and processing plant managers (n = 20), to assess the current pre- and postharvest Campylobacter interventions and control measures practiced by the industry for reducing Campylobacter contamination of broiler products. The survey also included information regarding each respondent's understanding of Campylobacter transmission and ecology in relation to broiler production. The results revealed that a majority of the establishments included in the survey are following the U.S. Department of Agriculture, Food Safety and Inspection Service guidelines for controlling Campylobacter contamination in broiler flocks and on carcasses. However, establishments appeared to be putting more effort into Salmonella control than into Campylobacter control both on the farm and in the processing plant. A majority of the respondents responded that current interventions are not effective for reducing Campylobacter contamination, especially on the farm. Many respondents did not understand the risk factors associated with Campylobacter colonization in broiler flocks and on carcasses. Continued educational and training programs for key stakeholders in the U.S. broiler industry are needed to increase awareness of the issues associated with Campylobacter infection in broiler chickens and of the fact that Campylobacter infection is a multifaceted problem that requires efforts from both the pre- and postharvest sectors.

HIGHLIGHTS

Oral administration of PLGA-encapsulated CpG ODN and Campylobacter jejuni lysate reduces cecal colonization by Campylobacter jejuni in chickens

Campylobacter jejuni (C. jejuni) is a major cause of bacterial food-borne illness in humans. It is considered a commensal organism of the chicken gut and infected chickens serve as a reservoir and shed bacteria throughout their lifespan. Contaminated poultry products are considered the major source of infection in humans. Therefore, to reduce the risk of human campylobacteriosis, it is essential to reduce the bacterial load in poultry products. The present study aimed to evaluate the protective effects of soluble and PLGA-encapsulated oligodeoxynucleotides (ODN) containing unmethylated CpG motifs (E-CpG ODN) as well as C. jejuni lysate as a multi-antigen vaccine against colonization with C. jejuni. The results revealed that oral administration of a low (5 µg) or high (50 µg) dose of CpG resulted in a significant reduction in cecal C. jejuni colonization by 1.23 and 1.32 log₁₀ (P < .05) in layer chickens, respectively, whereas E-CpG significantly reduced cecal C. jejuni colonization by 1.89 and 1.46 log₁₀ in layer and broiler chickens at day 22 post-infection (slaughter age in broilers), respectively. Similar patterns were observed for C. jejuni lysate; oral administration of C. jejuni lysate reduced the intestinal burden of C. jejuni in layer and broiler chickens by 2.24 and 2.14 log₁₀ at day 22 post-infection, respectively. Moreover, the combination of E-CpG and C. jejuni lysate reduced bacterial counts in cecal contents by 2.42 log₁₀ at day 22 post-infection in broiler chickens. Anti-C. jejuni IgG antibody (Ab) titers were significantly higher for broiler chickens receiving a low or high dose of E-CpG or a low dose of C. jejuni lysate than for chickens receiving the placebo. Furthermore, a positive correlation was observed between serum IgG Ab titers and cecal counts of C. jejuni in these groups. These findings suggest that PLGA-encapsulated CpG or C. jejuni lysate could be a promising strategy for control of C. jejuni in chickens.

Coadministration of the Campylobacter jejuni N-Glycan-Based Vaccine with Probiotics Improves Vaccine Performance in Broiler Chickens

Source attribution studies report that the consumption of contaminated poultry is the primary source for acquiring human campylobacteriosis. Oral administration of an engineered Escherichia coli strain expressing the Campylobacter jejuni N-glycan reduces bacterial colonization in specific-pathogen-free leghorn chickens, but only a fraction of birds respond to vaccination. Optimization of the vaccine for commercial broiler chickens has great potential to prevent the entry of the pathogen into the food chain. Here, we tested the same vaccination approach in broiler chickens and observed similar efficacies in pathogen load reduction, stimulation of the host IgY response, the lack of C. jejuni resistance development, uniformity in microbial gut composition, and the bimodal response to treatment. Gut microbiota analysis of leghorn and broiler vaccine responders identified one member of Clostridiales cluster XIVa, Anaerosporobacter mobilis, that was significantly more abundant in responder birds. In broiler chickens, coadministration of the live vaccine with A. mobilis or Lactobacillus reuteri, a commonly used probiotic, resulted in increased vaccine efficacy, antibody responses, and weight gain. To investigate whether the responder-nonresponder effect was due to the selection of a C. jejuni "supercolonizer mutant" with altered phase-variable genes, we analyzed all poly(G)-containing loci of the input strain compared to nonresponder colony isolates and found no evidence of phase state selection. However, untargeted nuclear magnetic resonance (NMR)-based metabolomics identified a potential biomarker negatively correlated with C. jejuni colonization levels that is possibly linked to increased microbial diversity in this subgroup. The comprehensive methods used to examine the bimodality of the vaccine response provide several opportunities to improve the C. jejuni vaccine and the efficacy of any vaccination strategy.IMPORTANCE Campylobacter jejuni is a common cause of human diarrheal disease worldwide and is listed by the World Health Organization as a high-priority pathogen. C. jejuni infection typically occurs through the ingestion of contaminated chicken meat, so many efforts are targeted at reducing C. jejuni levels at the source. We previously developed a vaccine that reduces C. jejuni levels in egg-laying chickens. In this study, we improved vaccine performance in meat birds by supplementing the vaccine with probiotics. In addition, we demonstrated that C. jejuni colonization levels in chickens are negatively correlated with the abundance of clostridia, another group of common gut microbes. We describe new methods for vaccine optimization that will assist in improving the C. jejuni vaccine and other vaccines under development.

Chicken Immune Response after In Ovo Immunization with Chimeric TLR5 Activating Flagellin of Campylobacter jejuni

Campylobacter jejuni is the main cause of bacterial food-borne diseases in developed countries. Chickens are the most important source of human infection. Vaccination of poultry is an attractive strategy to reduce the number of C. jejuni in the intestinal tract of chickens. We investigated the immunogenicity and protective efficacy of a recombinant C. jejuni flagellin-based subunit vaccine with intrinsic adjuvant activity. Toll-like receptor activation assays demonstrated the purity and TLR5 stimulating (adjuvant) activity of the vaccine. The antigen (20–40 μg) was administered in ovo to 18 day-old chicken embryos. Serum samples and intestinal content were assessed for antigen-specific systemic and mucosal humoral immune responses. In ovo vaccination resulted in the successful generation of IgY and IgM serum antibodies against the flagellin-based subunit vaccine as determined by ELISA and Western blotting. Vaccination did not induce significant amounts of flagellin-specific secretory IgA in the chicken intestine. Challenge of chickens with C. jejuni yielded similar intestinal colonization levels for vaccinated and control animals. Our results indicate that in ovo delivery of recombinant C. jejuni flagellin subunit vaccine is a feasible approach to yield a systemic humoral immune response in chickens but that a mucosal immune response may be needed to reduce C. jejuni colonization.

Campylobacter in Poultry: Ecology and Potential Interventions

Avian hosts constitute a natural reservoir for thermophilic Campylobacter species, primarily Campylobacter jejuni and Campylobacter coli, and poultry flocks are frequently colonized in the intestinal tract with high numbers of the organisms. Prevalence rates in poultry, especially in slaughter-age broiler flocks, could reach as high as 100% on some farms. Despite the extensive colonization, Campylobacter is essentially a commensal in birds, although limited evidence has implicated the organism as a poultry pathogen. Although Campylobacter is insignificant for poultry health, it is a leading cause of food-borne gastroenteritis in humans worldwide, and contaminated poultry meat is recognized as the main source for human exposure. Therefore, considerable research efforts have been devoted to the development of interventions to diminish Campylobacter contamination in poultry, with the intention to reduce the burden of food-borne illnesses. During the past decade, significant advance has been made in understanding Campylobacter in poultry. This review summarizes the current knowledge with an emphasis on ecology, antibiotic resistance, and potential pre- and postharvest interventions.

Evaluation of a polysaccharide conjugate vaccine to reduce colonization by Campylobacter jejuni in broiler chickens

Background

Campylobacter 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.

Results

The 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.

Conclusions

The 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.

Thermotolerant Campylobacter during Broiler Rearing: Risk Factors and Intervention

Thermotolerant Campylobacters are one of the most important bacterial causative agents of human gastrointestinal illness worldwide. In most European Union (EU) member states human campylobacteriosis is mainly caused by infection with Campylobacter jejuni or Campylobacter coli following consumption or inadequate handling of Campylobacter-contaminated poultry meat. To date, no effective strategy to control Campylobacter colonization of broilers during rearing is available. In this review, we describe the public health problem posed by Campylobacter presence in broilers and list and critically review all currently known measures that have been researched to lower the numbers of Campylobacter bacteria in broilers during rearing. We also discuss the most promising measures and which measures should be investigated further. We end this review by elaborating on readily usable measures to lower Campylobacter introduction and Campylobacter numbers in a broiler flock.

Intestinal colonization of broiler chickens by Campylobacter spp. in an experimental infection study

Consumption of poultry meat is considered as one of the main sources of human campylobacteriosis, and there is clearly a need for new surveillance and control measures based on quantitative data on Campylobacter spp. colonization dynamics in broiler chickens. We conducted four experimental infection trials, using four isolators during each infection trial to evaluate colonization of individual broiler chickens by Campylobacter jejuni over time. Individual and pooled faecal samples were obtained at days 4, 7 and 12 post-inoculation (p.i.) and caecal samples at day 12 p.i. There were large differences between broiler chickens in the number of C. jejuni in caecal and faecal material. Faecal samples of C. jejuni ranged from 4·0 to 9·4 log c.f.u./g and from 4·8 to 9·3 log c.f.u./g in the caeca. Faecal c.f.u./g decreased with time p.i. Most variation in c.f.u. for faecal and caecal samples was attributed to broiler chickens and a minor part to isolators, whereas infection trials did not affect the total variance. The results showed that pooled samples within isolators had lower c.f.u./g compared to the arithmetic mean of the individual samples. There was a significant correlation between faecal c.f.u./g at days 4 and 7 p.i., days 7 and 12 p.i. and for caecal and faecal c.f.u./g at day 12 p.i.

Pentavalent single-domain antibodies reduce Campylobacter jejuni motility and colonization in chickens

Campylobacter jejuni is the leading cause of bacterial foodborne illness in the world, with symptoms ranging from acute diarrhea to severe neurological disorders. Contaminated poultry meat is a major source of C. jejuni infection, and therefore, strategies to reduce this organism in poultry, are expected to reduce the incidence of Campylobacter-associated diseases. We have investigated whether oral administration of C. jejuni-specific single-domain antibodies would reduce bacterial colonization levels in chickens. Llama single-domain antibodies specific for C. jejuni were isolated from a phage display library generated from the heavy chain IgG variable domain repertoire of a llama immunized with C. jejuni flagella. Two flagella-specific single-domain antibodies were pentamerized to yield high avidity antibodies capable of multivalent binding to the target antigen. When administered orally to C. jejuni-infected two-day old chicks, the pentabodies significantly reduced C. jejuni colonization in the ceca. In vitro, the motility of the bacteria was also reduced in the presence of the flagella-specific pentabodies, suggesting the mechanism of action is through either direct interference with flagellar motility or antibody-mediated aggregation. Fluorescent microscopy and Western blot analyses revealed specific binding of the anti-flagella pentabodies to the C. jejuni flagellin.

Immunity to bacterial infection in the chicken

Bacterial infections remain important to the poultry industry both in terms of animal and public health, the latter due to the importance of poultry as a source of foodborne bacterial zoonoses such as Salmonella and Campylobacter. As such, much focus of research to the immune response to bacterial infection has been to Salmonella. In this review we will focus on how research on avian salmonellosis has developed our understanding of immunity to bacteria in the chicken from understanding the role of TLRs in recognition of bacterial pathogens, through the role of heterophils, macrophages and γδ lymphocytes in innate immunity and activation of adaptive responses to the role of cellular and humoral immunity in immune clearance and protection. What is known of the immune response to other bacterial infections and in particular infections that have emerged recently as major problems in poultry production including Campylobacter jejuni, Avian Pathogenic Escherichia coli, Ornithobacterium rhinotracheale and Clostridium perfringens are discussed.

Evaluation of nanoparticle-encapsulated outer membrane proteins for the control of Campylobacter jejuni colonization in chickens

Numerous vaccination strategies have been evaluated to develop effective vaccines against Campylobacter jejuni colonization in poultry but with limited success. The following experiments were conducted to investigate the effect of biodegradable and biocompatible poly (lactide-co-glycolide) nanoparticle (NP) encapsulated outer membrane proteins (OMP) of C. jejuni. Chickens were vaccinated with different routes [subcutaneous (s/c) or oral] and doses (25, 125, or 250 µg) of candidate nanoparticle vaccine with appropriate control groups. Serum and cloacal fecal samples were taken at regular intervals of time, and the birds were euthanized 7 d postchallenge with C. jejuni. The results were interpreted based on anti-OMP immunoglobulin response in chicken and intestinal colonization of C. jejuni. The C. jejuni colonization in cecal and cloacal contents at 7 d postchallenge was below the detection limit in the s/c vaccinated groups, but the other groups demonstrated varying degrees of colonization. The serum IgA was higher in the group vaccinated s/c with OMP only compared with the rest of the groups. The serum- and fecal-IgY titers were consistently higher in the s/c vaccinated groups (with or without NP) than the rest of the groups. Elevated levels of OMP specific serum antibodies correlated with below the limit of detection levels of Campylobacter colonization in broiler chickens receiving 125 μg of OMP alone and the OMP+NP vaccine s/c. In conclusion, the s/c route of vaccination with or without NP encapsulated OMP of C. jejuni may serve as a candidate vaccine for control of C. jejuni colonization in chickens.

Irrelevance between the induction of anti-Campylobacter humoral response by a bacterin and the lack of protection against homologous challenge in Japanese Jidori chickens

On-farm vaccination of chickens against Campylobacter jejuni is considered a potentially effective countermeasure to decrease campylobacteriosis via consumption of contaminated chicken meat, but is not yet available. In this study, 2 groups of Jidori chicks were immunized subcutaneously with a formalin-killed C. jejuni with 2 different adjuvants. Other chicks served as the unvaccinated control group. Both vaccines induced high levels of anti-Campylobacter IgG but did not decrease bacterial excretion in cecal droppings and bacterial load in the liver and spleen after oral challenge with 10(5) CFU of the homologous strain. Further study is needed to address the observed irrelevance and to develop a novel effective vaccine against C. jejuni.

Novel approaches for Campylobacter control in poultry

The Gram-negative bacterium Campylobacter is the most common bacterial cause of human gastroenteritis in the United States and many industrialized countries. Poultry, particularly chickens, is considered a major source of human campylobacteriosis. Thus, on-farm control of Campylobacter in poultry would reduce the risk of human exposure to this pathogen and have a significant impact on food safety and public health. To date, three general strategies have been proposed to control Campylobacter in poultry at the farm level: (1) reduction of environmental exposure (biosecurity measures), (2) an increase in poultry's host resistance to reduce Campylobacter carriage in the gut (e.g., competitive exclusion, vaccination, and host genetics selection), and (3) the use of antimicrobial alternatives to reduce and even eliminate Campylobacter from colonized chickens (e.g., bacteriophage therapy and bacteriocin treatment). Except for biosecurity measures, the other intervention approaches are currently not commercially available and are still under development. This review is focused on two promising strategies--vaccination and bacteriocin treatment. In particular, we extensively review recent research aimed at discovering and characterizing potent anti-Campylobacter bacteriocins to reduce Campylobacter load at the primary production level in poultry.

Vaccination of chickens against Campylobacter

The gram-negative bacterium Campylobacter is the leading cause of bacterial entero-colitis in humans and is associated with the occurrence of life-threatening auto-immune based neurological disorders. Chickens, which are often heavily colonized with Campylobacter without signs of pathology, are considered the most important source for human infection. Although vaccination is a well established and effective method to combat various microbes in poultry, a commercial vaccine against Campylobacter has not yet been developed. For the development of such a vaccine, three main challenges can be identified: (1) the identification of novel cross-protection-inducing antigens, (2) the induction of a rapid, potent immune response, and (3) the development of novel adjuvants to further stimulate immunity against Campylobacter. The rapidly emerging knowledge of the biology of Campylobacter in combination with the recent advances in the fields of molecular vaccinology and immunology provide the required setting for the development of an effective vaccine against Campylobacter in poultry.

Effect of Campylobacter-specific maternal antibodies on Campylobacter jejuni colonization in young chickens

Using laboratory challenge experiments, we examined whether Campylobacter-specific maternal antibody (MAB) plays a protective role in young chickens, which are usually free of Campylobacter under natural production conditions. Kinetics of C. jejuni colonization were compared by infecting 3-day-old broiler chicks, which were naturally positive for Campylobacter-specific MAB, and 21-day-old broilers, which were negative for Campylobacter-specific MAB. The onset of colonization occurred much sooner in birds challenged at the age of 21 days than it did in the birds inoculated at 3 days of age, which suggested a possible involvement of specific MAB in the delay of colonization. To further examine this possibility, specific-pathogen-free layer chickens were raised under laboratory conditions with or without Campylobacter infection, and their 3-day-old progenies with (MAB(+)) or without (MAB(-)) Campylobacter-specific MAB were orally challenged with C. jejuni. Significant decreases in the percentage of colonized chickens were observed in the MAB(+) group during the first week compared with the MAB(-) group. These results indicate that Campylobacter-specific MAB plays a partial role in protecting young chickens against colonization by C. jejuni. Presence of MAB in young chickens did not seem to affect the development of systemic immune response following infection with C. jejuni. However, active immune responses to Campylobacter occurred earlier and more strongly in birds infected at 21 days of age than those infected at 3 days of age. Clearance of Campylobacter infection was also observed in chickens infected at 21 days of age. Taken together, these findings (i) indicate that anti-Campylobacter MAB contributes to the lack of Campylobacter infection in young broiler chickens in natural environments and (ii) provide further evidence supporting the feasibility of development of immunization-based approaches for control of Campylobacter infection in poultry.

Quantitative risk assessment of human campylobacteriosis associated with thermophilic Campylobacter species in chickens

A quantitative risk assessment comprising the elements hazard identification, hazard characterization, exposure assessment, and risk characterization has been prepared to assess the effect of different mitigation strategies on the number of human cases in Denmark associated with thermophilic Campylobacter spp. in chickens. To estimate the human exposure to Campylobacter from a chicken meal and the number of human cases associated with this exposure, a mathematical risk model was developed. The model details the spread and transfer of Campylobacter in chickens from slaughter to consumption and the relationship between ingested dose and the probability of developing campylobacteriosis. Human exposure was estimated in two successive mathematical modules. Module 1 addresses changes in prevalence and numbers of Campylobacter on chicken carcasses throughout the processing steps of a slaughterhouse. Module 2 covers the transfer of Campylobacter during food handling in private kitchens. The age and sex of consumers were included in this module to introduce variable hygiene levels during food preparation and variable sizes and compositions of meals. Finally, the outcome of the exposure assessment modules was integrated with a Beta-Poisson dose-response model to provide a risk estimate. Simulations designed to predict the effect of different mitigation strategies showed that the incidence of campylobacteriosis associated with consumption of chicken meals could be reduced 30 times by introducing a 2 log reduction of the number of Campylobacter on the chicken carcasses. To obtain a similar reduction of the incidence, the flock prevalence should be reduced approximately 30 times or the kitchen hygiene improved approximately 30 times. Cross-contamination from positive to negative flocks during slaughter had almost no effect on the human Campylobacter incidence, which indicates that implementation of logistic slaughter will only have a minor influence on the risk. Finally, the simulations showed that people in the age of 18-29 years had the highest risk of developing campylobacteriosis.

Prevalence, antigenic specificity, and bactericidal activity of poultry anti-Campylobacter maternal antibodies

Poultry are considered the major reservoir for Campylobacter jejuni, a leading bacterial cause of human food-borne diarrhea. To understand the ecology of C. jejuni and develop strategies to control C. jejuni infection in the animal reservoir, we initiated studies to examine the potential role of anti-Campylobacter maternal antibodies in protecting young broiler chickens from infection by C. jejuni. Using an enzyme-linked immunosorbent assay (ELISA), the prevalence of anti-C. jejuni antibodies in breeder chickens, egg yolks, and broilers from multiple flocks of different farms were examined. High levels of antibodies to the organism were detected in serum samples of breeder chickens and in egg yolk contents. To determine the dynamics of anti-Campylobacter maternal antibody transferred from yolks to hatchlings, serum samples collected from five broiler flocks at weekly intervals from 1 to 28 or 42 days of age were also examined by ELISA. Sera from the 1-day and 7-day-old chicks showed high titers of antibodies to C. jejuni. Thereafter, antibody titers decreased substantially and were not detected during the third and fourth weeks of age. The disappearance of anti-Campylobacter maternal antibodies during 3 to 4 weeks of age coincides with the appearance of C. jejuni infections observed in many broiler chicken flocks. As shown by immunoblotting, the maternally derived antibodies recognized multiple membrane proteins of C. jejuni ranging from 19 to 107 kDa. Moreover, in vitro serum bactericidal assays showed that anti-Campylobacter maternal antibodies were active in antibody-dependent complement-mediated killing of C. jejuni. Together, these results highlight the widespread presence of functional anti-Campylobacter antibodies in the poultry production system and provide a strong rationale for further investigation of the potential role of anti-C. jejuni maternal antibodies in protecting young chickens from infection by C. jejuni.

Immunity, vaccination and the avian intestinal tract

Defence of the intestinal mucosal surface from enteric pathogens is initially mediated by secretory IgA (SIgA). As oral immunization of non-replicating antigen induces minimal SIgA antibody titers, novel immunization strategies which selectively induce mucosal immune responses in mammals are now being assessed in chickens. The strategies reviewed include the route of antigen delivery, the incorporation of antigenic components in delivery vehicles, the inclusion of immunomodulators in the vaccine formula or in the diet, and manipulation of intestinal microflora. The differences in anatomical organization and immunological mechanisms between birds and mammals must be considered when manipulating avian intestinal immunity with the latest immunotechnologies developed for mammals. Our knowledge of the function and functioning of the avian mucosal system is discussed. Progress in our understanding of this system, the location of precursor IgA B cells and antigen sampling by these sites is not as advanced as knowledge of the mammalian system, highlighting the need for ongoing research into the avian application of novel vaccination strategies.

Campylobacter jejuni--an emerging foodborne pathogen

Campylobacter jejuni is the most commonly reported bacterial cause of foodborne infection in the United States. Adding to the human and economic costs are chronic sequelae associated with C. jejuni infection--Guillian-Barré syndrome and reactive arthritis. In addition, an increasing proportion of human infections caused by C. jejuni are resistant to antimicrobial therapy. Mishandling of raw poultry and consumption of undercooked poultry are the major risk factors for human campylobacteriosis. Efforts to prevent human illness are needed throughout each link in the food chain.

Evaluation of the efficacy of intraperitoneal immunization in reducing Salmonella typhimurium infection in chickens

Conventional methods of parenteral immunization with killed bacterin vaccines have met with limited success in protecting the avian intestinal mucosa from pathogens such as Salmonella typhimurium. For mucosal vaccines to be successful they must be evaluated for their ability to stimulate local secretory immunoglobulin (SIgA) at the mucosal surface, which acts as the first line of defense against invading pathogens. Previously we have demonstrated the ability of i.p. immunization with nonreplicating antigen in an appropriate adjuvant to induce a primary immune response, which, after an oral booster immunization, stimulates enhanced intestinal IgA responses in chickens. In the experiments reported here we have applied this immunization protocol to vaccinate against S. typhimurium in chickens, and examined the protection provided against subsequent S. typhimurium challenge by placing vaccinated birds on seeded litter with cohabitant infected birds. Immunized+challenged birds displayed delayed onset of S. typhimurium infection, both at the mucosal surface and within the reticuloendothelial system. Elevated anti-S. typhimurium IgG and IgA titers were detected in serum after vaccination, which markedly increased after challenge, to levels higher than in control+challenged chickens. Anti-S. typhimurium IgA in bile and intestinal scrapings supernatant was also higher in the immunized+challenged birds than in the control+challenged birds 15 d after challenge. This study illustrates the potential for i.p. vaccination to induce a mucosal immune response to S. typhimurium in chickens, which, in the challenge model employed here, provided partial protection against intestinal challenge with the same pathogen and was reflected in deferred onset of bacterial infection and shedding.

The specificity of antibody in chickens immunised to reduce intestinal colonisation with Campylobacter jejuni

Poultry consumption has been identified as a major risk factor for human infection with Campylobacter jejuni in developed countries. C. jejuni is present in the gastrointestinal tract of broiler chickens at the time of slaughter, and faecal contamination of carcases during processing results in significant campylobacter loads on carcases. One approach to reducing the level of carcase contamination with C. jejuni is to control campylobacter infection in broiler chickens. To this end, the study described here investigated the specificity of antibody in serum and intestinal secretions of chickens that had been immunised with campylobacter antigens and then challenged with viable bacteria. The immunodominant antigens in the serum of birds that showed a 2-log reduction in caecal colonisation with C. jejuni included flagellin protein (61-63 Kd) and three additional antigens of 67, 73.5 and 77.5 Kd. Only flagellin and the 67 Kd antigen were recognised by IgG antibody in gastrointestinal secretions of the same birds. Antibody from chickens immunised with purified native flagellin protein recognised flagellin protein and the 67 Kd antigen in Western blots probed with serum, but only the flagellin proteins (61-63 Kd) in Westerns probed with gastrointestinal secretions. Analysis of the specificity of the response to flagellin protein using recombinant clones that expressed regions of the flagellin gene suggests that epitopes in each region of the flagellin protein were immunogenic. Of the immunodominant antigens, only flagellin appeared to be surface-exposed on viable C. jejuni, although conformational epitopes of flagellin appeared to be sensitive to the method of antigen purification. The results of this study suggest that flagellin and possibly the 67 Kd antigen may be valuable for immunological control of intestinal infection with C. jejuni in chickens, but that further work is required to purify these as vaccine candidates by using methods that preserve conformational epitopes.