Breeding to reduce susceptibility to Escherichia coli in layers

The impact of management practices on the disease and mortality rates of broilers and layers kept by small-scale farmers in Dodoma urban district, Tanzania

The demand for chicken products in Tanzania has increased due to population growth and rising incomes. As a result, the production of broilers and layers has been promoted to fill the gap due to their high productivity. However, exotic breeds of chicken are susceptible to diseases, thus requiring good disease management practices. The current study aimed to increase production of exotic breeds of chicken in the Dodoma region, which is growing rapidly, by identifying management factors associated with disease and chicken mortality. One hundred and four households that keep broilers or layers were selected randomly from the Dodoma urban district. The households were interviewed to gather information about chicken diseases, mortality, and management practices. The proportion of sick and dead chickens per farm was determined and used in beta regression to test its association with management practices and chicken breed. The proportion of sick chickens in a flock was low when stocking density was low and in large households, but it was higher when the farmer lacked knowledge of disease management. Further, mortality rates were high when farmers lacked disease knowledge and cleaning frequency was low, and low when farmers had extensive experience in chicken production. Improvement of extension services and education programmes for poultry farmers on good disease management practices is necessary to increase the production of layers and broilers in the region.

Comparison of the safety and efficacy of the wild-type and lpxL/lpxM mutant inactivated vaccine against the avian pathogenic Escherichia coli O1, O2, and O78 challenge

Avian pathogenic Escherichia coli (APEC) is primarily responsible for causing septicemia, pneumonitis, peritonitis, swollen head syndrome, and salpingitis in poultry, leading to significant losses in the poultry sector, particularly within the broiler industry. The removal of the lpxL and lpxM genes led to an eightfold decrease in the endotoxin levels of wild APEC strains. In this study, mutant strains of lpxL/lpxM and their O1, O2, and O78 wild-type strains were developed for an inactivated vaccine (referred to as the mutant vaccine and the wild-type vaccine, respectively), and the safety and effectiveness of these two prototype vaccines were assessed in white Leghorn chickens. Findings indicated that chickens immunized with the mutant vaccine showed a return of appetite sooner post-immunization and experienced earlier disappearance of nodules at the injection site compared to those immunized with the wild-type vaccine. Pathological examinations revealed that lesions were still present in the liver, lung, and injection site in chickens vaccinated with the wild-type vaccine 14 days post-vaccination (dpv), whereas no lesions were found in chickens vaccinated with the mutant vaccine at 14 dpv. There were no significant differences in antibody levels on the challenge day or in mortality or lesion scores between challenged birds immunized with either the mutant vaccine or the wild-type vaccine at the same dose. In this study, the safety of a single dose or overdose of the mutant vaccine and its efficacy at one dose were evaluated in broilers, and the results showed that the mutant vaccine had no adverse effects on or protected vaccinated broilers from challenge with the APEC O1, O2, or O78 strains. These results demonstrated that the mutant polyvalent inactivated vaccine is a competitive candidate against APEC O1, O2, and O78 infection compared to the wild-type vaccine.

Flock Factors Correlated with Elevated Mortality in Non-Beak Trimmed Aviary-Housed Layers

The use of non-cage housing systems for layers is increasing in Europe and elsewhere. Knowledge of factors that may affect mortality in these systems is important to be able to improve animal welfare, reduce mortality and enhance sustainability. The aim of this study was to investigate factors that may contribute to increased mortality in non-beak trimmed aviary-housed laying hens in Norway. A total of 39 non-beak trimmed commercial flocks (Lohmann LSL (n = 25) and Dekalb White (n = 14)) were visited between week 70 to 76 of life, and factors related to health, behaviour and management were recorded. Mean mortality in the flocks was 3% (range: 0.5−9%) and increased flock mortality was correlated with total feather loss (p < 0.05); feather loss on the breast (p < 0.02) and feather loss on the head (p < 0.003). There was an association between layer hybrid line and mortality (p = 0.055). Furthermore, a low positive correlation between mortality and dust level inside the barn was found (p < 0.04), showing that mortality was higher when dust level was also high. No correlation between mortality and the provision of environmental enrichment was found. In conclusion, this study found an association between flocks with elevated mortality (>3.0%) and increased feather loss which may indicate feather pecking. The results underline the importance of regularly assessment of plumage condition in commercial layer farms, as a tool to detect early signs of feather pecking in commercial aviary-housed layer flocks. This may help to target feather pecking before cannibalism breaks out.

Genetic resistance to avian pathogenic Escherichia coli (APEC): current status and opportunities

Infections with avian pathogenic Escherichia coli (APEC) can be extremely detrimental to poultry health and production. Investigating host genetic variation could identify the biological mechanisms that control resistance to this pathogen and allow selection for improved resistance in experimental and commercial poultry populations. In this review, the current knowledge of how host genetics contributes to APEC resistance and future opportunities that would benefit the understanding or application of genetic resistance are discussed. Phenotypes, such as antibody responses, lesion scores, and mortality, revealed that genetic background impacts APEC resistance and interacts with other factors including the environment and challenge conditions. Experiments have used divergent selection for APEC-specific antibody levels to facilitate genetic studies, estimated heritabilities in relevant traits, detected quantitative trait loci using microsatellites, and made associations with sequence variation in the major histocompatibility complex, which collectively suggest that improving APEC resistance through selection is feasible, although genetic control is partial, complex, and highly polygenic. Additionally, functional genomics techniques have identified antimicrobial responses, toll-like receptor and cytokine signalling, and the cell cycle as central pathways in the host response to APEC challenge. Opportunities for future research are discussed, including the expansion of existing lines of research and the application of new technologies that are relevant to the study of host genetics and APEC. This review closes with prospective strategies for improvement of host genetic resistance to APEC.

Advances in genetic selection and breeder practice improve commercial layer hen welfare

Modern commercial layer breeds represent the culmination of ~7000 years of natural genetic selection. This selection was driven in former times by a combination of genetic-shift and -drift events, that led to chickens being favoured as domesticated species for meat and egg production. More recently, in the early 20th century, the concept of hybrid vigour was discovered and accelerated the natural breeding progress that delivered new genetic lines and more favourable production traits. In the mid-20th century, the broiler-type and egg layer-type lines diverged and, in the 21st century, genetic analysis has further accelerated the progress made towards extended primary breeding characteristics such as egg quality, production and feed-intake traits, together with secondary breeding characteristics such as behavioural traits that have improved robustness in different housing systems, climates and feed types, which together have significantly improved welfare traits. Most recently, there has been the adoption of higher-powered computational analytics together with quantitative trait loci and single-nucleotide polymorphism assessment, which have further improved the uniformity of production traits within breeds. Most importantly, this has provided the primary breeding companies with improved and broader basis of selection of the modern commercial layer breeds, which also improved the alignment of layer strains with market requirements, and diverse variations in housing, nutritional and environmental conditions. This is also testament to the speed with which the commercial layer geneticists can respond to changing welfare policy on factors such as stocking density and beak treatment. The present paper reviews the modern approaches to genetic selection, including considerations of and benefits to the welfare state of commercial layers.

The Chicken MHC: Insights into Genetic Resistance, Immunity, and Inflammation Following Infectious Bronchitis Virus Infections

The chicken immune system has provided an immense contribution to basic immunology knowledge by establishing major landmarks and discoveries that defined concepts widely used today. One of many special features on chickens is the presence of a compact and simple major histocompatibility complex (MHC). Despite its simplicity, the chicken MHC maintains the essential counterpart genes of the mammalian MHC, allowing for a strong association to be detected between the MHC and resistance or susceptibility to infectious diseases. This association has been widely studied for several poultry infectious diseases, including infectious bronchitis. In addition to the MHC and its linked genes, other non-MHC loci may play a role in the mechanisms underlying such resistance. It has been reported that innate immune responses, such as macrophage function and inflammation, might be some of the factors driving resistance or susceptibility, consequently influencing the disease outcome in an individual or a population. Information about innate immunity and genetic resistance can be helpful in developing effective preventative measures for diseases such as infectious bronchitis, to which a systemic antibody response is often not associated with disease protection. In this review, we summarize the importance of the chicken MHC in poultry disease resistance, particularly to infectious bronchitis virus (IBV) infections and the role played by innate immunity and inflammation on disease outcome. We highlight how future studies focusing on the MHC and non-MHC genes can potentially bring clarity to observed resistance in some chicken B haplotype lines.

Assessing MHC-B diversity in Silkie chickens

The major histocompatibility complex (MHC) is a highly polymorphic region on chromosome 16, which contains numerous immune response genes, and is known to influence disease susceptibility and resistance in chickens. Variability of MHC-B haplotypes in various well-known and commercially utilized breeds has previously been identified. This study aims to understand MHC-B diversity in the Silkie breed using a high-density SNP panel that encompasses the chicken MHC-B region. DNA was obtained from 74 females and 27 males from a commercial Silkie breeder colony that is maintained through minimal genetic selection practices. A previously described panel of 90 SNPs, all located within the MHC-B region, was used to evaluate MHC-B variability in the commercial Silkie breeder colony. MHC-B haplotypes identified from the individual SNP information in the Silkie colony were compared to published haplotypes from the same region. Of the 27 haplotypes identified in the Silkie population, 8 have been previously described. Nineteen haplotypes are unique to the Silkie population and include one novel recombinant and 2 additional possible novel recombinants. Six haplotypes were found at a frequency greater than 5% of the population, of which 4 are novel. Finally, Hardy Weinberg Equilibrium (HWE) was calculated for the observed haplotypes, which were found to be in HWE. This study shows considerable MHC-B diversity in the Silkie breed and adds further information on variability of the MHC-B region in the chicken.

Advances in methodologies for detecting MHC-B variability in chickens

The chicken major histocompatibility B complex (MHC-B) region is of great interest owing to its very strong association with resistance to many diseases. Variation in the MHC-B was initially identified by hemagglutination of red blood cells with specific alloantisera. New technologies, developed to identify variation in biological materials, have been applied to the chicken MHC. Protein variation encoded by the MHC genes was examined by immunoprecipitation and 2-dimensional gel electrophoresis. Increased availability of DNA probes, PCR, and sequencing resulted in the application of DNA-based methods for MHC detection. The chicken reference genome, completed in 2004, allowed further refinements in DNA methods that enabled more rapid examination of MHC variation and extended such analyses to include very diverse chicken populations. This review progresses from the inception of MHC-B identification to the present, describing multiple methods, plus their advantages and disadvantages.

Selective breeding for high natural antibody level increases resistance to avian pathogenic Escherichia coli (APEC) in chickens

Keyhole limpet hemocyanin (KLH)-binding natural antibody (NAb) titers in chickens are heritable, and higher levels have previously been associated with a higher survival. This suggests that selective breeding for higher NAb levels might increase survival by means of improved general disease resistance. Chickens were divergently selected and bred for total NAb levels binding KLH at 16 weeks of age for six generations, resulting in a High NAb selection line and a Low NAb selection line. To for test differences in disease resistance, chickens were challenged with avian pathogenic Escherichia coli (APEC) in two separate experiments. Chickens at 8 days of age received one of four intratracheal inoculations of 0.2 mL phosphate buffered saline (PBS): 1) mock inoculate, 2) with 0.2 mL PBS containing 10^8.20 colony-forming units (CFU)/mL APEC, 3) with 0.2 mL PBS containing 10^6.64 CFU/mL APEC, and 4) with 0.2 mL PBS containing 10^7.55 CFU/mL APEC. Mortality was recorded during 7 days post inoculation. Overall, 50-60% reduced mortality was observed in the High line compared to the Low line for all APEC doses. In addition, morbidity was determined of the surviving chickens at 15 days of age. The High line had lower morbidity scores compared to the Low line. We conclude that selective breeding for high KLH-binding NAb levels at 16 weeks of age increase APEC resistance in early life. This study and previous studies support the hypothesis that KLH-binding NAb might be used as an indicator trait for to selective breed for general disease resistance in an antigen non-specific fashion.

Dose-dependent differential resistance of inbred chicken lines to avian pathogenic Escherichia coli challenge

Avian pathogenic E. coli (APEC) cause severe respiratory and systemic disease. To address the genetic and immunological basis of resistance, inbred chicken lines were used to establish a model of differential resistance to APEC, using strain O1 of serotype O1:K1:H7. Inbred lines 7₂, 15I and C.B12 and the outbred line Novogen Brown were inoculated via the airsac with a high dose (10⁷ colony-forming units, CFU) or low dose (10⁵ CFU) of APEC O1. Clinical signs, colibacillosis lesion score and bacterial colonization of tissues after high dose challenge were significantly higher in line 15I and C.B12 birds. The majority of the 15I and C.B12 birds succumbed to the infection by 14 h post-infection, whilst none of the line 7₂ and the Novogen Brown birds developed clinical signs. No difference was observed after low dose challenge. In a repeat study, inbred lines 7₂ and 15I were inoculated with low, intermediate or high doses of APEC O1 ranging from 10⁵ to 10⁷ CFU. The colonization of lung was highest in line 15I after high dose challenge and birds developed clinical signs; however, colonization of blood and spleen, clinical signs and lesion score were not different between lines. No difference was observed after intermediate or low dose challenge. Ex vivo, the phagocytic and bactericidal activity of lung leukocytes from line 7₂ and 15I birds did not differ. Our data suggest that although differential resistance of inbred lines 7₂, 15I and C.B12 to APEC O1 challenge is apparent, it is dependent on the infectious dose. Research Highlights Lines 15I and C.B12 are more susceptible than line 7₂ to a high dose of APEC O1. Differential resistance is dose-dependent in lines 15I and 7₂. Phagocytic and bactericidal activity is similar and dose independent.

Genetic approach to select against embryo mortality caused by Enterococcus faecalis infection in laying hens

Selection to reduce susceptibility to Enterococcus faecalis infection in laying hens may contribute to the prevention of amyloid arthropathy since it is mainly induced by this bacterium. Therefore, the aim of the present study was to investigate the possibility to select more laying hens that are resistant against E. faecalis infection through the embryo lethality assay (ELA), which is proposed as an alternative model to replace the adult avian challenge assay. Ten-day-old embryos of 500 Lohmann Brown layers were inoculated into the allantoic cavity with an infectious dose of 2.5 colony-forming units (cfu)/mL of the avian E. faecalis strain K923/96 in 3 ELAs. The embryonic mortality rate (EMR) was determined by candling the eggs daily over a period of 4 d. The average EMR estimated during the 3 ELAs was 50% and the highest EMR occurred 3 to 4 d post inoculation. The estimated heritability for embryonic survivability to the infection was h2 = 0.12-0.14, calculated with the logistic and probit link function, respectively, indicating that the selection of more laying hens that are resistant to E. faecalis infection is feasible. A highly negative genetic correlation was estimated between embryonic survivability and laying performance at the peak of lay (rg = -0.22) and at the end of the production (rg = -0.65), as well as with breaking strength (rg = -0.30 to -0.37). A positive correlation was found between egg weight and the embryonic survivability (rg = +0.16), and no genetic correlation was found with body weight and dynamic stiffness. Therefore, although it was demonstrated that it is possible to breed for E. faecalis resistance, special care should be taken to monitor and to take all traits and their genetic correlations into account in order to achieve a balanced genetic progress. Besides, the ELA does not require that the hens are exposed to pathogens thereby saving labor and cost. Therefore, it could be feasible that ELA be implemented in selection programs.

The efficacy of inactivated Escherichia coli autogenous vaccines against the E. coli peritonitis syndrome in layers

Autogenous Escherichia coli vaccines to prevent the E. coli peritonitis syndrome (EPS) in laying hens are often used in the field, although their effectiveness has not been demonstrated yet. Therefore, in this study, which consisted of two experiments, their efficacy was assessed. In the first experiment, the EPS-inducing ability of three E. coli isolates originating from bone marrow of hens that died due to EPS and with different Pulsed-Field Gel Electrophoresis patterns, was examined by intravenous inoculation of the isolates in 17-week-old brown layers. Based on the results one isolate was chosen for the preparation of the vaccines and for homologous challenge and another one for heterologous challenge performed in the second experiment. In the named experiment, groups of laying hens which had been vaccinated intramuscularly at 14 and 18 weeks of age with inactivated vaccine either formulated as aqueous suspension or as water-in-oil emulsion were homologously or heterologously challenged per aerosol at 30 weeks of age. The vaccines contained ≥10^8.2 formaldehyde-inactivated colony-forming units (cfu) of E. coli per hen dose in 0.5 ml. The estimated E. coli challenge dose uptake ranged from 10^5.8 to 10^6.5 cfu per hen. Groups consisted of 18 hens each and were housed in separate isolators from 27 weeks of age. Control groups were included in this experiment, which was ended eight days after challenge. Vaccinations had no effect on body growth and both vaccine types induced (almost) complete protection against homologous challenge, while protection against heterologous challenge was inconclusive.

Expression of Inflammatory and Cell Death Program Genes and Comet DNA Damage Assay Induced by Escherichia coli in Layer Hens

Modern methods of industrial poultry and egg production systems involve stressful practices that stimulate Escherichia coli (E. coli) activity causing endotoxic shock. This investigation was conducted to evaluate the expression of pro-inflammatory cytokines and cell death program genes and DNA damage induced by E. coli in the brain and liver tissues of laying hens. A total of two hundred and ten H&N brown layer hens with 20 week age, were used in this research. First, preliminary experiments were designed (60 hens in total) to establish the optimal exposure dose of E. coli and to determine the nearest time of notable response to be used in the remainder studies of this research. At 35-wk of age, 150 hens were randomly assigned into 2 groups with 3 replicates of 25 birds each; the first group was injected in the brachial wing vein with 10⁷E. coli colony/hen, while the second group was injected with saline and served as a control. The body temperature and plasma corticosterone concentration were measured 3 hr after injection. Specimens of liver and brain were obtained from each group and the gene expression of p38 mitogen-activated protein kinase, interlukin-1β (IL-1β), tumor necrosis factor alpha (TNF-α), Bax, and caspase-3 genes were measured by quantitative real-time PCR. DNA damage in the brain and liver tissues were also measured by comet assay. Hens treated with E. coli showed significant (P<0.05) increase of body temperature and plasma corticosterone (42.6°C and 14.5 ng/ml, respectively) compared to the control group (41.1°C and 5.5 ng/ml, respectively). Additional remarkable over-inflammation gene expression of p38, IL-1β and TNF-α.genes were also detected in the brain (2.2-fold, 2.0-fold and 3.3-fold, respectively) and the liver (2.1-fold, 1.9-fold and 3.0-fold, respectively) tissues of the infected chickens. It is also important to note that hens injected with E. coli showed an increase in DNA damage in the brain and liver cells (P<0.05). These results were synchronized with activating cell death program since our data showed significant high expression of Bax gene by 2.8- and 2.7-fold and caspase-3 gene by 2.5- and 2.7-fold in the brain and liver tissues of infected chickens, respectively (P<0.05). In conclusion, the current study indicates that E. coli injection induces inflammatory physiological response and triggers cell death program in the brain and liver. Our results provide more understanding to endotoxic shock by E. coli in chickens at cellular level. Further studies are required to confirm if such responses are destructive or protective to set the means through which a chicken mounts a successful defense against avian pathogenic E. coli.

Experimental induced avian E. coli salpingitis: Significant impact of strain and host factors on the clinical and pathological outcome

Several types of Escherichia coli have been associated with extra-intestinal infections in poultry, however, they may vary significantly in their virulence potential. The aim of the present study was to investigate the virulence of five strains of E. coli obtained from different disease manifestations or from the cloacae of a healthy chicken. The virulence potential of the strains were evaluated in an avian experimental model for ascending infections, and experiments were conducted in both layers and broiler breeders. The clinical outcome of infection was highly depending on the challenge strain, however, not significantly reflecting the origin of the strain. In general, broiler breeders had a more severe clinical outcomes of infection compared to layers, but major with-in group diversity was observed for all challenge strains of clinical origin. A single strain of ST95 (phylogroup B2) had a distinct ability to cause disease. Results of the study shows major differences in virulence of different strains of E. coli in ascending infections; however, there was no indication of tissue-specific adaptation, since strains obtained from lesions unrelated to the reproductive system were fully capable of causing experimental infection. In conclusion, the study provides evidence for the clinical outcome of infection with E. coli in poultry is largely influenced by the specific strain as well as individual host factors.

Brief review of the chicken Major Histocompatibility Complex: the genes, their distribution on chromosome 16, and their contributions to disease resistance

Nearly all genes presently mapped to chicken chromosome 16 (GGA 16) have either a demonstrated role in immune responses or are considered to serve in immunity by reason of sequence homology with immune system genes defined in other species. The genes are best described in regional units. Among these, the best known is the polymorphic major histocompatibility complex-B (MHC-B) region containing genes for classical peptide antigen presentation. Nearby MHC-B is a small region containing two CD1 genes, which encode molecules known to bind lipid antigens and which will likely be found in chickens to present lipids to specialized T cells, as occurs with CD1 molecules in other species. Another region is the MHC-Y region, separated from MHC-B by an intervening region of tandem repeats. Like MHC-B, MHC-Y is polymorphic. It contains specialized class I and class II genes and c-type lectin-like genes. Yet another region, separated from MHC-Y by the single nucleolar organizing region (NOR) in the chicken genome, contains olfactory receptor genes and scavenger receptor genes, which are also thought to contribute to immunity. The structure, distribution, linkages and patterns of polymorphism in these regions, suggest GGA 16 evolves as a microchromosome devoted to immune defense. Many GGA 16 genes are polymorphic and polygenic. At the moment most disease associations are at the haplotype level. Roles of individual MHC genes in disease resistance are documented in only a very few instances. Provided suitable experimental stocks persist, the availability of increasingly detailed maps of GGA 16 genes combined with new means for detecting genetic variability will lead to investigations defining the contributions of individual loci and more applications for immunogenetics in breeding healthy poultry.

Selection for pro-inflammatory mediators yields chickens with increased resistance against Salmonella enterica serovar Enteritidis

Salmonella is a leading cause of foodborne illness and can be transmitted through consumption of contaminated poultry; therefore, increasing a flock's natural resistance to Salmonella could improve food safety. Previously, we characterized the heterophil-mediated innate immune response of 2 parental broiler lines and F1 reciprocal crosses and showed that increased heterophil function and expression of pro-inflammatory mediators corresponds with increased resistance against diverse pathogens. A preliminary selection trial showed that individual sires had varying inherent levels of pro-inflammatory mediators and selection based on a high or low phenotype was passed onto progeny. Based on these results, we hypothesized selection of broilers for higher levels of the pro-inflammatory mediators IL-6, CXCLi2, and CCLi2 would produce progeny with increased resistance against Salmonella Enteritidis. Peripheral blood leukocytes were isolated from 75 commercial broiler sires, screened, and 10 naturally high and low expressing sires were selected and mated to randomly selected dams to produce the first generation of "high" and "low" progeny. The mRNA expression of CXCLi2 and CCLi2 were significantly (P ≤ 0.02) higher in the high progeny and were more resistant to liver and spleen organ invasion by Salmonella Enteritidis compared with low progeny. Production of the second generation yielded progeny that had differences (P ≤ 0.03) in all 3 mediators and further improved resistance against Salmonella Enteritidis. Feed conversion ratio and percent breast meat yield were calculated and were equal, whereas the high birds weighed slightly, but significantly, less than the low birds. These data clearly demonstrate that selection based on a higher phenotype of key pro-inflammatory mediators is a novel means to produce broilers that are naturally more resistant to Salmonella, one of the most important foodborne pathogens affecting the poultry industry.

Broiler lines divergently selected for digestive efficiency also differ in their susceptibility to colibacillosis

Increasing feed efficiency of broiler chickens by selective breeding could lead to decreased feed cost and reduced environmental impact of poultry production. At INRA, two broiler chicken lines (D+/D-) were divergently selected for their digestive efficiency. Strong differences were shown between both lines for the anatomy and histology of the digestive tract, and for the intestinal microbiota composition. In the present study, we investigated whether this selection also had an effect on susceptibility to colibacillosis, which is one of the main causes of economic losses in poultry production. The broiler lines D+/D- were challenged with an avian pathogenic Escherichia coli strain. A first experiment was conducted to assess the 50% lethal dose by subcutaneous infection of hatchlings, whereas a second experiment reproduced colibacillosis by infecting air sacs of 23-day-old chicks. The 50% lethal dose was very low for both lines. However, the line with the higher digestive efficiency (D+) was the less susceptible to colibacillosis. This result is interesting for selection purposes and opens the way to integrative genetic studies of the interactions between digestion efficiency and resistance to colibacillosis.

Pathogenicity of H3N8 influenza viruses isolated from domestic ducks in chickens with or without Escherichia coli coinfections

Influenza viruses from domestic aquatic birds can be transmitted to chickens, resulting in continued prevalence of the disease. H3 viruses are one of the most frequently identified subtypes in domestic ducks. Results from our previous serologic study suggested that H3 virus infections potentially exist in chickens with a wide geographical distribution in China. To better understand their pathogenic potential, two H3N8 influenza viruses isolated from domestic ducks were selected for experimental infections in chickens. We found that viral shedding lasted for at least 14 days postinfection for both viruses; however, one virus caused mortality in the chickens when coinfected with Escherichia coli. Sequencing of the viral HA gene isolated from the inoculated chickens revealed two amino acid mutations within the gene. These findings demonstrate the pathogenicity of the H3N8 domestic duck influenza viruses to chickens, highlighting the need for routine epidemiologic investigations of H3 subtype influenza viruses in chicken populations.

Leukocyte transcriptome from chickens infected with avian pathogenic Escherichia coli identifies pathways associated with resistance

Avian pathogenic Escherichia coli (APEC) causes colibacillosis, which is responsible for morbidity and mortality in chickens. Gene expression patterns have previously been demonstrated to differ between chicken populations that are resistant vs. susceptible to bacterial infection, but little is currently known about gene expression response to APEC. Increased understanding of gene expression patterns associated with resistance will facilitate genetic selection to increase resistance to APEC. Male broiler chicks were vaccinated at 2 weeks of age and challenged with APEC at 4 weeks of age. Peripheral blood leukocytes were collected at 1 and 5 day post-infection. Lesions on the liver, pericardium, and air sacs were used to assign a mild or severe pathology status to non-vaccinated, challenged chicks. Ten treatment groups were therefore generated with a priori factors of vaccination, challenge, day post-infection, and the a posteriori factor of pathology status. Global transcriptomic response was evaluated using the Agilent 44K chicken microarray. APEC infection resulted in more up-regulation than down-regulation of differentially expressed genes. Immune response and metabolic processes were enriched with differentially expressed genes. Although vaccination significantly reduced lesions in challenged bird, there was no detectable effect of vaccination on gene expression. This study investigated the transcriptomic differences in host responses associated with mild vs. severe pathology, in addition to the effects of vaccination and challenge, thus revealing genes and networks associated with response to APEC and providing a foundation for future studies on, and genetic selection for, genetic resistance to APEC.

Characterization of Escherichia coli isolates from laying hens with colibacillosis on 2 commercial egg-producing farms in Korea

The present study reports on layer chickens with colibacillosis in 2 commercial egg-producing farms (referred to as farm A and farm B, which were managed by the same owner and were about 1 km apart) in the middle region of the Korean peninsula. The 2 flocks were infected at the initiation of egg laying. They were characterized by no previous clinical signs but sudden mortality (2.7-4.0%), with severe lesions of septicemia and fibrinous polyserositis. Escherichia coli was isolated from the lesions of the infected birds. Serotyping tests identified isolates that belonged to somatic groups O1 (12/17), O46 (2/17), O78 (1/17), and O84 (1/17) or that were unidentified (1/17). Thirteen of 17 E. coli isolates (76.4%) obtained from 11 birds in the 2 flocks showed similar pulsed-field gel electrophoresis patterns that were arbitrarily designated as pattern A. The isolates had high frequencies of putative virulence genes including 100% [fimC (type 1 fimbriae), iucD (aerobactin synthesis), and iss (increased serum survival)], 94.1% [cva/cvi (structural genes of colicin V operon) and vat (vacuolating autotransporter toxin)], 88.2% [irp2, iron-repressible protein (yersinia bactin) synthesis, and fyuA, ferric yersinia uptake], and 82.3% [tsh (temperature-sensitive hemagglutinin)]; astA (encoding a heat-stable cytotoxin associated with enteroaggregative E. coli) was not associated with the enteric disorder. These data suggest that all chickens with colibacillosis on farms A and B were likely infected by E. coli strains that are highly pathogenic in avian species.