The avian haemophili

Avibacterium paragallinarum, the Causative Agent of Infectious Coryza: A Comprehensive Review

Infectious coryza (IC) caused by Avibacterium paragallinarum (AP) has risen in importance as a poultry disease over the past several years because of its increased incidence in commercial poultry in both Europe and the United States. Because of this rise in importance, more attention has been focused on diagnosis, isolation, and surveillance of this bacterial pathogen. As a result, new knowledge has been produced and published. This review was compiled with the main purpose of summarizing and presenting the updated knowledge available about AP. However, the new knowledge can only be understood in the context of previously known facts about the disease. Therefore, this review has been organized in two major parts. The first part is a review of the established knowledge about AP, followed by recent updates. In the first part, we summarize the established well-known as well as some of the less-known facts and literature about AP. The second section focuses on specifics of the latest IC outbreaks in commercial poultry in northern latitudes, particularly in Europe and in North America. Additionally, we reviewed the current geographical distribution of the disease in Asia, South America, and Africa. The crises created by emerging or re-emerging disease outbreaks ignite interest in understanding the disease and pathogen in order to combat it properly. This results in new knowledge that improves the understanding of the disease features, leading to improved disease prevention, control, and eradication. Although knowledge about AP has advanced, knowledge gaps about the disease still persist. Therefore, this review concludes with summarizing the current knowledge gaps as well as potential areas for future research.

Development and Validation of PCR Assays for Improved Diagnosis of Infectious Coryza by Differentiating Pathogenic and Nonpathogenic Avibacterium paragallinarum

Avibacterium paragallinarum (AP) is a primary bacterial pathogen of chickens that leads to infectious coryza (IC) disease. Recently, multiple commercial layer flocks in several U.S. states reported positive real-time quantitative PCR (qPCR) results without any history of clinical signs. Owing to the proven specificity of the current IC qPCR assays, these results suggested the existence of AP strains that do not lead to clinical disease in layers, i.e., nonpathogenic AP (npAP) strains. This was further proven by isolating and characterizing npAP strains from these normal layer flocks. Although these strains are clinically nonpathogenic in layers, current IC qPCR assays fail to distinguish them from the pathogenic AP, leading to qPCR-positive flocks with no apparent disease. Therefore, the purpose of this study was to develop and validate TaqMan real-time PCR assays that can differentiate between pathogenic and the newly discovered npAP strains. Whole-genome sequences of six npAP isolates were generated, and genomic comparison was conducted against 43 pathogenic AP strains. Analysis revealed two consistent features. First, the capsular polysaccharide transporter gene hctA was exclusively present in the pathogenic AP strains but absent in npAP strains. Second, unique lengthy insertions within the HMTp210 gene were observed only in the npAP strains. The HMTp210 insertions were chosen as the qPCR target to identify the newly discovered npAP strains (np-HMTp210 assay). On the other hand, hctA was selected to identify the pathogenic AP strains. During the validation process, 28 isolates and 10 oropharyngeal (OP) swab pools representing the pathogenic AP strains as well as six isolates and 86 OP pools of npAP strains were tested. A wide panel of respiratory, bacterial and viral, pathogens were included in the validation. Both assays demonstrated high performance in terms of analytical specificity in relation to each other and when tested against various bacterial and viral pathogens. Moreover, the hctA and np-HMTp210 assays displayed high sensitivity, with a limit of detection of 1 copy/µl and 2.5 copies/µl, respectively, and PCR efficiencies of 94.62% and 92.99%, respectively. Both assays showed 100% diagnostic specificity and sensitivity. However, after the validation process, an ongoing surveillance effort in clinically normal layer flocks uncovered a new population of npAP strains. This new npAP population refutes our original qPCR design goals to distinguish AP strains from npAP strains because the latest finding renders the differential capacity of this newly developed PCR incomplete. However, the newly developed qPCR in its current status is still useful in differentiating the great majority of cases and is still useful for diagnostic laboratories to provide much needed IC diagnostic answers to the poultry industry. Meanwhile, we will continue to investigate new targets that could either complement or replace the current targets to achieve our goal of the complete differentiation between these two AP populations.

Identification and characterization of biosynthetic loci of lipooligosaccharide and capsular polysaccharide in Avibacterium paragallinarum

Infectious coryza is an acute respiratory disease in chickens caused by Avibacterium paragallinarum. Lipooligosaccharides (LOSs) and capsular polysaccharides are important components of Av. paragallinarum. Herein, we identified that gene cluster L6 and two genes waaF, waaQ were associated with LOS synthesis, and two genes acbD and ccbF1 were involved in capsular synthesis. Mutant and complementary strains of these genes were generated by natural transformation. Wild-type strains produced LOS that yielded an upper and lower band. In comparison, ΔwaaQ and ΔwaaF yielded a truncated lower band and lacked the upper band, while ΔL6 did not exhibit the upper band, and the lower band was identical to that of the wild-type strain. The survival rates of wild-type strain, ΔwaaF, ΔwaaQ, and ΔL6 in chicken serum were 4.89 % ± 0.27 %, 0.0013 % ± 0.0002 %, 0.43 % ± 0.05 %, and 3.1 % ± 0.35 %, respectively. Notably, the resistances of ΔwaaF, ΔwaaQ, and ΔL6 to chicken serum were significantly lower than that of parent strain. By contrast, the survival rate of the ΔacbD strain was 55.17 % ± 0.61 %, and its resistance to chicken serum was significantly higher than that of the wild-type strain (p < 0.001). Deletion of the waaF, waaQ, L6, acbD, and ccbF1 genes resulted in enhanced formation of biofilm without altering immunogenicity in chickens. The ΔwaaF, ΔwaaQ, and ΔccbF1 strains exhibited heightened susceptibility to fowlicidin-2. Furthermore, ΔwaaF, ΔacbD, and ΔccbF1 strains shown a decrease in pathogenicity (p < 0.05). These results are valuable for advancing research on the pathogenesis of Av. paragallinarum.

Common viral and bacterial avian respiratory infections: an updated review

Many pathogens that cause chronic diseases in birds use the respiratory tract as a primary route of infection, and respiratory disorders are the main leading source of financial losses in the poultry business. Respiratory infections are a serious problem facing the poultry sector, causing severe economic losses. Avian influenza virus, Newcastle disease virus, infectious bronchitis virus, and avian pneumovirus are particularly serious viral respiratory pathogens. Mycoplasma gallisepticum, Staphylococcus, Bordetella avium, Pasteurella multocida, Riemerella anatipestifer, Chlamydophila psittaci, and Escherichia coli have been identified as the most serious bacterial respiratory pathogens in poultry. This review gives an updated summary, incorporating the latest data, about the evidence for the circulation of widespread, economically important poultry respiratory pathogens, with special reference to possible methods for the control and prevention of these pathogens.

The Protective Efficacy of an Inactivated Vaccine against Avibacterium paragallinarum Field Isolates

Infectious coryza (IC) is an acute respiratory disease caused by Avibacterium paragallinarum (Av. paragallinarum). In recent years, there have been frequent outbreaks of IC in chickens vaccinated with an inactivated vaccine, causing huge losses to the poultry industry. In this study, the protective efficacy of the trivalent inactivated IC vaccine (PT Medion Farma Jaya) against the field isolates of three serovars of Av. paragallinarum was verified. After vaccination, the hemagglutination inhibition antibody titers in double-vaccinated groups (A2, B2, and C2) were higher than those in single-vaccinated groups (A1, B1, and C1). The highest antibody titer was 213.1 at 3 weeks after the booster vaccination in group A2. Consistent with the trend in hemagglutination inhibition antibody titers, the protective efficacy of double vaccination was better than that of single vaccination. The clinical symptoms and pathological changes were alleviated, or the bacterial shedding was significantly reduced with double vaccination after challenge with field isolates of three serovars (p < 0.05). In particular, the chickens with double vaccination showed no clinical symptoms, pathological changes, or bacterial shedding after challenge by the serovar C strain. There was no significant difference in body weight and egg production between the double-vaccinated groups and the negative control group (p > 0.05). Therefore, we recommend that the commercial IC vaccine should be double-vaccinated in clinical applications.

Identification and characterization of Dutch Avibacterium paragallinarum isolates and the implications for diagnostics

This study reports the results of diagnostic and molecular typing methods for 18 Avibacterium paragallinarum isolates obtained from outbreaks of infectious coryza in commercial layer flocks in the Netherlands. Isolation, biochemical identification, species-specific PCR tests and classical serotyping were performed. In addition, molecular typing by Enterobacterial Repetitive Intergenic Consensus-Based Polymerase Chain Reaction (ERIC-PCR) and sequence analysis of the partial HPG2 region of A. paragallinarum were applied and results of both techniques were compared. Moreover, the pathogenicity of an isolate of the most common genotype detected in the Netherlands was determined in an animal experiment. All 18 Avibacterium isolates were nicotinamide adenine dinucleotide-dependent. All isolates were detected by the species-specific conventional PCR while 33% of the isolates were missed by the species-specific real-time PCR. Sequence analysis showed a probe mismatch as a result of a single nucleotide polymorphism (G1516A). Modification of the probe of the real-time PCR was necessary to overcome false negative results. Molecular typing showed that sequence analysis of the partial HPG2 region was in concordance with ERIC-PCR results and indicated the presence of two major genotypes. Serotyping showed the presence of serovars A-1, A-2 and B-1. There was no correlation between genotyping results and serotyping results. Inoculation of an isolate of the most prevalent genotype, and belonging to serovar A-1, into brown layer hens demonstrated the pathogenicity of this isolate.

Early migration pattern of Avibacterium paragallinarum in the nasal passage of experimentally infected chicken and Japanese quail by immunohistochemistry

Infectious coryza (IC) is often a curse for poultry farmers when it occurs concurrently with several pathogens causing swollen head syndrome. The disease is caused by Avibacterium paragallinarum, which inflicts initial damage to the nasal and respiratory epithelium. This facilitates the progression of disease pathology across the nasal cavity, thereby providing a platform for multiplication of opportunistic microbes. In this study, we attempted to investigate the early entrance and migration pattern of A. paragallinarum in chicken and Japanese quail following experimental infection, by employing an in-house developed polyclonal antiserum against this pathogen. Antigenic-specificity of the raised antiserum was subsequently evaluated through immune-dot blot techniques and counter-current immunoelectrophoresis (CIE). The resultant antiserum characterized the antigen localization within formalin-fixed and partially decalcified nasal tissue sections though immunohistochemistry (IHC). Japanese quail showed prominent localization of the bacterial antigen at 12 h post-infection in anterior turbinates. However, the chicken exhibited a higher level of the bacterial pathogen with intense immuno-reactivity at 24 and 48 h post-inoculation. The decline in immunostaining intensity in the nasal tissue of chicken as well as Japanese quail by 72 h post-infection signifies either an attempt to resolve the infection by the resident immune cells across the nasal passage of the host, or its dissipation by certain inherent innate immune factors present across the nasal passage that are still unknown to us. In the present study, we used a moderately virulent pathogen (A. paragallinarum) that inflicted a mild to moderate degree of damage to histo-architecture of the nasal passage and provided a discernible migratory pattern with fewer alterations, along with provision toward unravelling basics of the immuno-pathogenetic mechanism. This knowledge will support efforts towards the development of a future mucosal nasal vaccine in birds affected with IC.

The development and application of a blocking ELISA kit for the diagnosis of infectious coryza

A blocking enzyme-linked immunosorbent assay (B-ELISA) kit for the diagnosis of infectious coryza was developed in this study. The kit was based on a recently described blocking ELISA that uses monoclonal antibodies to achieve specificity for antibodies to either Haemophilus paragallinarum serovar A or serovar C. The results showed that the B-ELISA kit detected 96 and 90%, respectively, of chickens vaccinated or challenged with H. paragallinarum serovar A. When used on chickens vaccinated or challenged with H. paragallinarum serovar C, the kit detected 77 and 40%, respectively, as positive. The majority of sera from vaccinated chickens were still positive on the serovars A and C ELISAs 4 months after vaccination. Based on pen trial data, the serovar A B-ELISA kit had a sensitivity of 95% and a specificity of 100%. The serovar C B-ELISA kit had a sensitivity of 73% and a specificity of 100%. A range of field sera was examined with the kit, generating results that correlated with the known vaccination/disease history of the flocks examined. As freeze drying the monoclonal antibodies and the conjugate had some effect on optimal working concentration, the kit used liquid solutions of these two reagents. The kit could be stored for 7 days at 37 degrees C, 10 months at 4 degrees C and more than 1 yearat -20 degrees C. Our results suggest that the kit would be a useful aid in the diagnosis of infectious coryza in China and other countries where H. paragallinarum serovars A and C are the predominant or sole serovars.

Monoclonal antibody characterization of reference isolates of different serogroups of Haemophilus paragallinarum

Previously, a panel of five monoclonal antibodies (Mabs) was used to study the antigens of strains 0083, 0222 and Modesto of Haemophilus paragallinarum and marked antigenic differences were noted. To establish if these differences were serogroup specific, more reference strains were examined with these Mabs. It was not possible to detect any relationship between the antigens recognized by the Mabs and the serogroup of the reference strain. None of the Mabs produced reacted with the haemagglutinins of the reference strains. The F1 Mab detected an outer membrane protein of 39 kDa, while the V1 Mab detected a lipopolysaccharide of between 13.8 to 14 kDa. Mabs VF1 and VF2 both recognized antigens of 39 kDa of unknown chemical nature and with extremely low frequency of occurrence among strains and isolates. The VF3 Mab detected a lipopolysaccharide with multiple bands at 37 to 39 kDa, which broke down after freezing and thawing to multiple bands of 29 to 32 kDa. These results imply that the haemagglutinins, which are the major typing and protective antigens remain undetected by this panel of Mabs.

Vaccination of one-day-old broiler chicks against infectious coryza

In order to evaluate the protection conferred by an experimental inactivated vaccine against infectious coryza, three challenge trials were undertaken using 112 1-day-old broilers. The vaccine "Hepa Inmuno NC" included bacterial antigens of Avibacterium paragallinarum (serogroups A, B, variant B, and C) as well as antigens of Newcastle virus and hepatitis virus. Fifty-six broiler chicks were vaccinated at the first day of life at the hatchery while another 56 chicks were left unvaccinated. Three infection trials were conducted simultaneously using each of the three serogroups A, B, or C of Av. paragallinarum. In each trial, 17 vaccinated and 17 unvaccinated broilers were used. Challenge was performed at day 31 of life by injection, into the left infraorbital sinus, of approximately 1 x 10(5) colony forming units of the corresponding Av. paragallinarum strain. Clinical signs were recorded on day 2 postchallenge. All broilers were euthanatized and both infraorbital sinuses were bacteriologically examined for the presence of Av. paragallinarum on day 5 postchallenge. In comparison with the unvaccinated broilers, the vaccine significantly reduced the number of broilers with clinical signs after challenge with serogroup B, and significantly fewer vaccinated broilers were positive for the presence of Av. paragallinarum after challenge with serogroup C. On the other hand, no significant protection was observed when broilers were challenged with Av. paragallinarum from serogroup A. Despite the high infection rates in vaccinated chicks after an experimental infection with Av. paragallinarum, it was possible to reduce colonization of Av. paragallinarum (serogroup B) and clinical signs (serogroup C) in broiler chicks by vaccination at the first day of life. Further cross-protection trials should be done, including other Av. paragallinarum strains in the vaccine, especially those from serogroup A.

The cloning and sequencing of the UDP-galactose 4-epimerase gene (galE) from Avibacterium paragallinarum

The putative uridine diphosphate (UDP)-galactose 4-epimerase encoding gene, galE, was isolated from Avibacterium paragallinarum with the use of degenerate primers, colony hybridization and inverse PCR. The data revealed an open reading frame of 1017 bp encoding a protein of 338 amino acids with a molecular weight of 37 kDa and an isoelectric point of 5.5. High sequence homology was obtained with an 87, 91 and 89% sequence identity on protein level towards the galE genes from Actinobacillus pleuropneumoniae, Haemophilus influenza and Pasteurella multocida, respectively. To verify that the cloned galE gene encodes for a UDP-galactose 4-epimeras, this gene was cloned into the pYES-2 expression vector, followed by transformation in a Saccharomyces cerevisiae gal10 deletion strain. Complementation of the gal10 deletion mutant with the galE gene confirmed that this gene encodes a UDP-galactose 4-epimerase.

A comparison of a blocking ELISA and a haemagglutination inhibition assay for the detection of antibodies to Avibacterium (Haemophilus) paragallinarum in sera from artificially infected chickens

The ability of blocking ELISAs and haemagglutination-inhibition (HI) tests to detect antibodies in sera from chickens challenged with either Avibacterium (Haemophilus) paragallinarum isolate Hp8 (serovar A) or H668 (serovar C) was compared. Serum samples were examined weekly over the 9 weeks following infection. The results showed that the positive rate of serovar A specific antibody in the B-ELISA remained at 100% from the second week to the ninth week. In chickens given the serovar C challenge, the highest positive rate of serovar C specific antibody in the B-ELISA appeared at the seventh week (60% positive) and was then followed by a rapid decrease. The B-ELISA gave significantly more positives at weeks 2, 3, 7, 8 and 9 post-infection for serovar A and at week 7 post-infection for serovar C. In qualitative terms, for both serovar A and serovar C infections, the HI tests gave a lower percentage of positive sera at all time points except at 9 weeks post-infection with serovar C. The highest positive rate for serovar A HI antibodies was 70% of sera at the fourth and fifth weeks post-infection. The highest rate of serovar C HI antibodies was 20% at the fifth and sixth weeks post-infection. The results have provided further evidence of the suitability of the serovar A and C B-ELISAs for the diagnosis of infectious coryza.

Differential distribution of novel restriction-modification systems in clonal lineages of Neisseria meningitidis

Using representational difference analysis, we isolated novel meningococcal restriction-modification (R-M) systems. NmeBI, which is a homologue of the R-M system HgaI of Pasteurella volantium, was present in meningococci of the ET-5 complex and of lineage III. NmeAI was found in serogroup A, ET-37 complex, and cluster A4 meningococci. NmeDI was harbored by meningococci of the ET-37 complex and of cluster A4, but not by serogroup A meningococci. Two of the R-M systems, NmeBI and NmeDI, were located at homologous positions between the phenylalanyl-tRNA synthetase genes pheS and pheT, which appeared to be a preferential target for the insertion of foreign DNA in meningococci. The distribution of the three R-M systems was tested with 103 meningococcal strains comprising 49 sequence types. The vast majority of the strains had either NmeBI, NmeAI, or both NmeAI and NmeDI. Using cocultivation experiments, we could demonstrate that NmeBI, which was present in ET-5 complex meningococci, was responsible for a partial restriction of DNA transfer from meningococci of the ET-37 complex to meningococci of the ET-5 complex.

A comparative study of the major outer membrane proteins of the avian haemophili and Pasteurella gallinarum

A polyclonal antibody prepared against the 35 kDa outer membrane protein (a putative porin) of Pasteurella (P.) multocida revealed binding to the 36 kDa major outer membrane protein (major Omp) of Haemophilus (H.) paragallinarum, to the 38 kDa major Omp of P.gallinarum, to the 39 kDa major Omp of P.volantium and to the 38.5 kDa major Omp of P. avium in immunoblotting studies. Comparison of N-terminal amino acid sequences also confirmed the relationship between the major Omps of most of the members of the family Pasteurellaceae.

Ecology and significance of Pasteurellaceae in animals

The reservoir of eighty-one taxa/groups classified with the family Pasteurellaceae Pohl 1981 is reviewed based upon published data and own investigations. With the exception of certain strains of P. multocida, A. pleuropneumoniae and [H.] paragallinarum organisms belonging to this family are usually regarded as opportunistic, secondary invaders which under normal conditions coexist peacefully with the animal host on mucosal membranes of the upper respiratory- and lower genital tracts. Very little is known about factors that govern the ecological preferences that certain members of this family show for specific surfaces and hosts. Mechanisms of colonization, survival and multiplication, invasion and pathogenic action are incompletely understood. The significance of Pasteurellaceae in animals and man has recently been reviewed. Subsequent publications have underlined the significance of biovars 2 of P. canis and P. avium and ornithine negative P. multocida in pneumonia in cattle. In addition, differences in pathogenicity have been demonstrated for different serovars of [H.] parasuis. The disease potential of many taxa/groups is only incompletely known.