Salmonella enterica serovar enteritidis burden in broiler breeder chicks genetically associated with vaccine antibody response

Direct and maternal genetic effects for preinflection point growth traits and humoral immunity in quail

Early growth traits in quails are considered as the growth performances before the inflection point which are genetically different from body weights (BW) at later stages. Moreover, in addition to growth performance, humoral immunity is moderately heritable and is considered in some breeding programs. However, estimating the direct genetic, particularly the maternal genetic correlations between growth and immunity in quail, are not studied sufficiently, which were the aims of the present study. The quails' BW were recorded at hatch (BW0) to 25 d of age with a 5-d interval and body weight gains (BWG) were measured as average growth performance of the birds in a 5-d period. Antibody titer against Newcastle disease virus (IgN) was measured through the hemagglutination inhibition (HI) test. For titration of anti-SRBC antibodies (IgY and IgM), a hemagglutination microtiter assay was used. In general, growth records in 4,181 birds and humoral immune responses in 1,023 birds were assigned to the study. The genetic parameters were estimated by single-trait analysis via Gibb's sampling. After finding the best model for each trait, multi-trait analysis was done to estimate the direct and maternal genetic correlations. Direct heritabilities (h²) were estimated to be moderate for BW (0.481-0.551) and BWG (0.524-0.557), while h² for immune responses were low (0.035-0.079). Maternal environmental effect (c²) was only significant for BW0, BW5, and BWG0-5. Maternal heritabilities (m²) for BW and BWG were all lower than corresponding h², ranging from 0.072 (BW25) to 0.098 (BW0). The m² for IgN (0.098) was more than 2.5 times greater than h² (0.040) for this trait. Direct (r_a) and maternal (r_m) genetic correlations between IgN-BW, IgY-BW, and IgY-BWG were negative, while ra and rm for IgM-BW, IgN-BWG, and IgM-BWG were positive. The r_a between humoral immune responses were low to moderate and rm was significant only for IgY-IgM (0.339). Given positive genetic correlations in BWG-IgN and BWG-IgM as well as positive genetic correlations between both IgN and IgM with IgY, it is suggested that including the BWG in the breeding programs would directly result in the improvement of the birds' growth performance. It would also contribute indirectly to the improvement of the birds' humoral immune responses.

Toward integrative genomics study of genetic resistance to Salmonella and Campylobacter intestinal colonization in fowl

Salmonella enterica serotypes Enteritidis and Typhimurium and Campylobacter jejuni are responsible for most cases of food poisoning in Europe. These bacteria do not cause severe disease symptoms in chicken, but they are easily propagated by symptomless chicken carriers which cannot be easily isolated. This animal tolerance is detrimental to food safety. In this particular case, increasing animal's resistance is not sufficient, since some animals considered as resistant are able to carry bacteria during several weeks without displaying disease symptoms. We review studies aimed at evaluating the resistance of chicken to Salmonella and Campylobacter intestinal colonization, either a few days or several weeks after infection. While studies of the genetic control of Campylobacter colonization are only beginning, mostly due to technical difficulties in infection protocols, genetic studies of Salmonella colonization have been conducted for now more than 20 years. They have initially reported an estimation of the genetic parameters associated with resistance to Salmonella colonization and are now aimed at identifying the genomic regions controlling variation of this trait in experimental lines and commercial populations. With the advent of high-throughput genomics, we are closer than ever to identify the true genes controlling resistance to Enterobacteria colonization in chicken. The comparison of genes involved in early resistance to intestinal colonization with genes controlling resistance to bacteria persistence several weeks after infection (i.e., carrier-state) should soon highlight the differences between the molecular mechanisms underlying those two distinct phenotypes. It will also be highly interesting to compare the genes or genomic regions controlling Campylobacter and Salmonella, in order to evaluate the feasibility of a selection conducted on both bacteria simultaneously.

Efficacy of several vaccination programmes in commercial layer and broiler breeder hens against experimental challenge with Salmonella enterica serovar Enteritidis

Two experiments were performed to evaluate the protective effect of various vaccination combinations given at 5 and 9 weeks of age against experimental challenge with Salmonella enterica serovar Enteritidis (SE) phage type 4 at 12 weeks of age. In Experiment 1, groups of commercial layers were vaccinated by one of the following programmes: Group 1, two doses of a SE bacterin (Layermune SE); Group 2, one dose of a live Salmonella enterica serovar Gallinarum vaccine (Cevac SG9R) followed by one dose of the SE bacterin; Group 3, one dose of each of two different multivalent inactivated vaccines containing SE cells (Corymune 4K and Corymune 7K; and Group 4, unvaccinated, challenged controls. In Experiment 2, groups of broiler breeders were vaccinated by the same programmes as Groups 1 and 2 above while Group 3 was an unvaccinated, challenged control group. All vaccination programmes and the challenge induced significant (P < 0.05) seroconversion as measured by enzyme-linked immunosorbent assay. Overall, in both experiments, all vaccination schemes were significantly effective in reducing organ (spleen, liver and caeca) colonization by the challenge strain as well as reducing faecal excretion for at least 3 weeks. Vaccinated layers in Groups 1 and 2 and broiler breeders in Group 2 showed the greatest reduction in organ colonization and the least faecal excretion. In Experiment 1, layers vaccinated with multivalent inactivated vaccines containing a SE component (Group 3) were only moderately protected, indicating that such a vaccination programme may be useful in farms with good husbandry and housing conditions and low environmental infectious pressure by Salmonella.

Genetic control of resistance to salmonellosis and to Salmonella carrier-state in fowl: a review

Salmonellosis is a frequent disease in poultry stocks, caused by several serotypes of the bacterial species Salmonella enterica and sometimes transmitted to humans through the consumption of contaminated meat or eggs. Symptom-free carriers of the bacteria contribute greatly to the propagation of the disease in poultry stocks. So far, several candidate genes and quantitative trait loci (QTL) for resistance to carrier state or to acute disease have been identified using artificial infection of S. enterica serovar Enteritidis or S. enterica serovar Typhimurium strains in diverse genetic backgrounds, with several different infection procedures and phenotypic assessment protocols. This diversity in experimental conditions has led to a complex sum of results, but allows a more complete description of the disease. Comparisons among studies show that genes controlling resistance to Salmonella differ according to the chicken line studied, the trait assessed and the chicken's age. The loci identified are located on 25 of the 38 chicken autosomal chromosomes. Some of these loci are clustered in several genomic regions, indicating the possibility of a common genetic control for different models. In particular, the genomic regions carrying the candidate genes TLR4 and SLC11A1, the Major Histocompatibility Complex (MHC) and the QTL SAL1 are interesting for more in-depth studies. This article reviews the main Salmonella infection models and chicken lines studied under a historical perspective and then the candidate genes and QTL identified so far.

MHC haplotype and susceptibility to experimental infections (Salmonella Enteritidis, Pasteurella multocida or Ascaridia galli) in a commercial and an indigenous chicken breed

In three independent experimental infection studies, the susceptibility and course of infection of three pathogens considered of importance in most poultry production systems, Ascaridia galli, Salmonella Enteritidis and Pasteurella multocida were compared in two chicken breeds, the indigenous Vietnamese Ri and the commercial Luong Phuong. Furthermore, the association of the Major Histocompatibility Complex (MHC) with disease-related parameters was evaluated, using alleles of the LEI0258 microsatellite as markers for MHC haplotypes. The Ri chickens were found to be more resistant to A. galli and S. Enteritidis than commercial Luong Phuong chickens. In contrast, the Ri chickens were more susceptible to P. multocida, although production parameters were more affected in the Luong Phuong chickens. Furthermore, it was shown that the individual variations observed in response to the infections were influenced by the MHC. Using marker alleles of the microsatellite LEI0258, which is located within the MHC region, several MHC haplotypes were identified as being associated with infection intensity of A. galli. An association of the MHC with the specific antibody response to S. Enteritidis was also found where four MHC haplotypes were shown to be associated with high specific antibody response. Finally, one MHC haplotype was identified as being associated with pathological lesions and mortality in the P. multocida experiment. Although not statistically significant, our analysis suggested that this haplotype might be associated with resistance. These results demonstrate the presence of local genetic resources in Vietnamese chickens, which could be utilized in breeding programmes aiming at improving disease resistance.

Observations on Salmonella contamination of eggs from infected commercial laying flocks where vaccination for Salmonella enterica serovar Enteritidis had been used

Eggs were collected monthly from 12 cage-layer flocks on four farms where Salmonella Enteritidis was present in vaccinated flocks despite vaccination with an S. Enteritidis bacterin. Where possible, hens were also taken for culture at the end of the laying period, and faecal and environmental samples were taken from the laying houses before and after cleaning and disinfection. Twenty-four batches of six egg shells from the 13 652 tested (0.18% [0.11 to 0.26 CI(95)] single egg equivalent) were positive for S. Enteritidis and 54 (0.40% [0.30 to 0.52 CI(95)] single egg equivalent) for other serovars. Six batches of 13 640 (0.04% [0.02 to 0.10 CI95] single egg equivalent) egg contents, bulked in six egg pools, contained S. Enteritidis and three batches contained other serovars. In addition three further batches contained S. Enteritidis in both contents and shells, and two other batches contained other serovars in both. The total level of contamination by S. Enteritidis of both contents and shells found in vaccinated flocks was therefore 33 batches/13 682 eggs(0.24% [0.17 to 0.34 CI(95)] single egg equivalent). The total of contamination for any Salmonella serovar was 92 batches/13 682 eggs (0.68% [0.55 to 0.84 CI(95)] single egg equivalent). These results contrast with the findings of testing of eggs from three unvaccinated flocks prior to this study where 21 batches of egg shells from a total of 2101 eggs (1.0% [0.63 to 1.56 CI(95)] single egg equivalent) and six batches of contents from 2051 eggs (0.29% [0.11 to 0.64 CI95] single egg equivalent) were contaminated with S. Enteritidis. S. Enteritidis was found in 67/699 (9.6%) of vaccinated spent hens and 64/562 (11.4%) of bulked fresh faecal samples taken from laying houses. Failure to adequately clean and disinfect laying houses and to control mice appeared to be a common feature on the farms.

Analyses of Five gallinacin genes and the Salmonella enterica serovar Enteritidis response in poultry

Gallinacins in poultry are functional equivalents of mammalian beta-defensins, which constitute an integral component of the innate immune system. Salmonella enterica serovar Enteritidis is a gram-negative bacterium that negatively affects both human and animal health. To analyze the association of genetic variations of the gallinacin genes with the phenotypic response to S. enterica serovar Enteritidis, an F1 population of chickens was created by crossing four outbred broiler sires to dams of two highly inbred lines. The F1 chicks were evaluated for bacterial colonization after pathogenic S. enterica serovar Enteritidis inoculation and for circulating antibody levels after inoculation with S. enterica serovar Enteritidis bacterin vaccine. Five candidate genes were studied, including gallinacins 2, 3, 4, 5, and 7. Gene fragments were sequenced from the founder individuals of the resource population, and a mean of 13.2 single-nucleotide polymorphisms (SNP) per kilobase was identified. One allele-defining SNP per gene was utilized to test for statistical associations of sire alleles with progeny response to S. enterica serovar Enteritidis. Among the five gallinacin genes evaluated, the Gal3 and Gal7 SNPs in broiler sires were found to be associated with antibody production after S. enterica serovar Enteritidis vaccination. Utilization of these SNPs as molecular markers for the response to S. enterica serovar Enteritidis may result in the enhancement of the immune response in poultry.

An attenuated Salmonella Enteritidis strain derivative of the main genotype circulating in Uruguay is an effective vaccine for chickens

We have recently reported that Salmonella enterica serovar Enteritidis (S. Enteritidis) strains circulating in Uruguay, are unevenly distributed among different genetic subtypes, with a predominant genotype that is a common contaminant of poultry-derived food and that accounts for the vast majority of human cases of food-borne disease. Herein, we describe the construction of a genetically-defined aroC derivative (LVR02) of a local strain of S. Enteritidis belonging to the major genetic type. We demonstrated the attenuation and the immunogenicity of that strain in a mouse model, and evaluated it as a vaccine for commercial layer chickens. LVR02 proved to be stable, attenuated, innocuous, immunogenic and to induce protective immunity against a S. Enteritidis challenge when used for oral vaccination. A single oral dose of LVR02 administered to newly hatched chickens induced protection against oral challenge with the parental virulent strain, preventing systemic and persistent intestinal infection and significantly reducing the shedding of the challenge strain in birds' feces. A second vaccine dose at 15 days post-hatching boosted the immunogenicity of the vaccine, and strengthened the protection achieved with a single dose. This strain may represent the basis of a live vaccine to be included in national control programs to reduce circulation of this pathogen in the country.

Analysis of Chicken TLR4, CD28, MIF, MD-2, and LITAF Genes in a Salmonella enteritidis Resource Population

Salmonella enteritidis is a foodborne pathogen that negatively affects both animal and human health. Genetic variations in response to pathogenic SE colonization or to SE vaccination were measured in a chicken resource population. Outbred broiler sires and 3 diverse, highly inbred dam lines produced 508 F1 progeny that were evaluated for either bacterial colonization after pathogenic SE inoculation or circulating antibody level after SE vaccination. Five candidate genes were selected for study, based on their biological function as possibly affecting response to SE: toll-like receptor 4 (TLR4), T-cell specific surface protein (CD28), macrophage migration inhibitory factor (MIF), MD-2, and lipopolysaccharide-induced tumor necrosis factor (TNF)-alpha factor (LITAF). Gene fragments were sequenced from the founder lines of the resource population. The LITAF and MIF genes were homozygous for all sires. Single nucleotide polymorphisms (SNP) were identified in 3 genes (TLR4, CD28, and MD-2) and were used to test for associations of sire SNP with SE response. Linear mixed models were used for statistical analyses. The CD28 broiler sire SNP was associated with both bacterial load in the cecum (P < 0.003) and vaccine antibody response (P < 0.05). The MD-2 SNP was associated (P < 0.04) with the bacterial load in the spleen. The use of these SNP in these genes in marker-assisted selection may result in enhancement of disease resistance.

Association of transforming growth factor beta genes with quantitative trait loci for antibody response kinetics in hens

Antibody responses (primary and secondary phases) were measured in an F2 population. The resource population was derived from grandsires of two highly inbred major histocompatibility complex (MHC)-congenic Fayoumi chicken lines (named M5.1 and M15.2) mated with highly inbred Leghorn G-B1 hens. Secondary phase parameters of maximum titres (Ymax) and time required to achieve Ymax (Tmax) were estimated from post-secondary titres by using a non-linear regression model. Associations of single nucleotide polymorphisms (SNP) in transforming growth factor beta2 (TGFB2), 3, and 4 genes with antibody response parameters were evaluated. Multiple immune response parameters were significantly associated with the TGFB2 gene primarily in the lineage of the M5.1 grandsire, suggesting that TGFB2 or linked genes affect antibody response in hens. Significant main effects of the three genes were mostly found in the lineage of the M5.1 grandsire. Significant two-way interactions on antibody response were primarily detected between TGFB3 and TGFB4 genes, and in the lineage of the M15.2 grandsire. Effects preferentially detectable in only one of the MHC-congenic lineages suggest that there was interaction between the MHC and TGFB genes. The characterized TGFB SNPs might be applied in marker-assisted selection to improve antibody production.

Chicken MHC class I and II gene effects on antibody response kinetics in adult chickens

The major histocompatibility complex (MHC) plays an important role in regulation of the immune response. The MHC class I and II genes were selected as candidates to investigate associations with vaccine response to Salmonella enteritidis and kinetics of antibody response to sheep red blood cell (SRBC) and Brucella abortus. Primary antibody response after S. enteritidis vaccination at day 10, and antibody response to SRBC and killed B. abortus after immunization at 19 and 22 weeks were measured in an F2 population. The resource population was derived from males of two highly inbred MHC-congenic Fayoumi chicken lines (M5.1 and M15.2) mated with highly inbred G-B1 Leghorn line hens. Secondary phase parameters of minimum titers ( Y(min)), maximum titers ( Y(max)), and time needed to achieve Y(min) ( t(min)) and Y(max) ( t(max)) were estimated from post-secondary titers by using a non-linear regression model. Associations of single nucleotide polymorphisms (SNPs) in MHC class I and II genes with antibody response parameters were determined by a general linear model. Significant associations were found primarily in the M15.2 grandsire haplotype. There were significant associations between MHC class I alpha(1) and alpha(2) SNPs and antibody response to S. enteritidis, primary antibody response to B. abortus, Y(min) to SRBC, and Y(max) to both SRBC and B. abortus. There were significant effects of the MHC class II beta(1) domain SNP on S. enteritidis antibody and Y(max) to SRBC. The results suggest that the characterized SNPs might be used in future applications by marker-assisted selection to improve vaccine response and immunocompetence in chickens.

Associations of interferon-gamma genotype and protein level with antibody response kinetics in chickens

Although previous studies have demonstrated an association between interferon-gamma (IFN-gamma) promoter genotype and antibody response kinetics in chickens, the protein levels that may mediate such a gene-trait association have not been determined. The objective of this study, therefore, was to determine the correlation of circulating IFN-gamma levels with both the IFN-gammaIFN-gamma promoter polymorphisms and antibody response in order to evaluate the potential role of IFN-gamma protein in mediating genetic control of antibody response in chickens. Antibody response after Salmonella enteritidis (SE) vaccination at day 10, antibody response to sheep red blood cells (SRBCs) and killed Brucella abortus after immunizations at 19 wk and 22 wk, and serum IFN-gamma protein level were measured in an F2 population derived from inbred lines. A single nucleotide polymorphism in the IFN-gamma promoter region was associated with IFN-gamma protein expression as measured by an enzyme-linked immunosorbent assay after both primary and secondary immunizations. Higher IFN-gamma protein level was correlated with higher antibody level to SE and with increased maximum level and decreased time to reach the maximum secondary antibody response to SRBCs. These results suggest that one of the mechanisms by which promoter polymorphism of IFN-gamma affects antibody production in chickens may involve the circulating level of IFN-gamma protein.