Hemagglutinin serotyping of Avibacterium paragallinarum isolates from Ecuador

Pathogenicity of Avibacterium paragallinarum Strains from Peru and the Selection of Candidate Strains for an Inactivated Vaccine

Worldwide, Avibacterium paragallinarum is the aetiological agent of infectious coryza in poultry. Vaccines are the best means of control, helping reduce clinical signs and colonization of this bacterium. Most vaccines are based on international reference strains, or, lately, regional strains, but, generally, without any information regarding their virulence. The characterization of the pathogenicity of 24 Av. paragallinarum strains of the three Page serogroups, including four variant strains of serogroup B, all isolated from infectious coryza outbreaks in Peru, was performed. After experimental inoculation into the infraorbital sinuses, information regarding their capacity to induce infectious coryza typical clinical signs, spreading, and colonization was recorded. Furthermore, after intraperitoneal inoculation, septicaemia and death were registered. Differences among strains in these parameters were observed, even within strains from the same serogroup. Finally, the four most pathogenic strains, one from each serogroup, were chosen to formulate an experimental vaccine that was tested successfully against homologous challenges in reducing clinical signs and colonization in vaccinated birds compared to unvaccinated ones. This is the first time that Av. paragallinarum strains from Peru were studied thoroughly for their virulence in a search for improving vaccine formulation.

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.

Selection of Avibacterium paragallinarum Page serovar B strains for an infectious coryza vaccine

Infectious coryza is an important respiratory disease of chickens around the world and is caused by Avibacterium paragallinarum. Among the three Page serovars currently recognized for this bacterium, serovar B is a major circulating serovar in China nowadays. The cross-protection ability of the Page serovar B reference strain (0222) and five local isolates was evaluated by a vaccination-challenge trial in SPF chickens. The clinical signs seen in control birds challenged by strain 0222 and isolate HB 01 were significantly different, with isolate HB 01 giving more severe clinical signs. In terms of cross-protection, the protection in the groups vaccinated with isolate HB 01 and BJ 02 was significantly higher than that in the groups vaccinated with 0222 and the other three isolates. In addition, an experimental oil adjuvant trivalent vaccine, containing field isolate HB 01 antigen, was compared for immune efficacy with two commercial trivalent infectious coryza vaccines containing internationally recognized serovar B strains. The experimental oil adjuvant trivalent vaccine elicited best protection (80%) among the three trivalent vaccines. In conclusion, the oil adjuvant vaccine, containing field isolate HB 01 may be a better choice in control of current serovar B Av. paragallinarum outbreaks in China under current circumstances.

Virulence of Serovar C-1 Strains of Avibacterium paragallinarum

The bacterium Avibacterium paragallinarum is the etiologic agent of infectious coryza of chickens. There are nine serovars of A. paragallinarum , and serovar C-1 has emerged in outbreaks of infectious coryza in layer hens in the Americas, with all isolates having been obtained from infectious coryza-vaccinated chickens. In the current study, the clinical and histopathologic outcomes of experimental infections in chickens with A. paragallinarum of serovar C-1 were investigated. The Japanese serovar reference strain, H-18, and a Mexican isolate, ESV-135, were included in the study. No differences in clinical sign scores or morbidity were observed between the two strains. The two bacterial strains caused microscopic lesions of lymphoplasmacytic inflammation in the mucosa of the nasal cavity, infraorbital sinus, and trachea. Similar severe lesions were observed in birds inoculated with both H-18 and ESV-135 strains. The lesions were present 48 hr after inoculation and persisted until day 10 after inoculation. Slight to severe, extensive hemorrhages were observed in the lumen, mucous membranes, and lamina propria of the nasal cavity and infraorbital sinus in most of the chickens inoculated with either the reference strain H-18 or the ESV-135 isolate. Hemorrhages in the upper respiratory tract of chickens experimentally infected with A. paragallinarum are reported here for the first time. The results have confirmed the high virulence of the reference strain H-18 as previously reported and have shown that the Mexican isolate was as virulent as the reference strain. The virulence of A. paragallinarum isolates may play a role in explaining why severe infectious coryza outbreaks are being seen in both vaccinated and nonvaccinated chicken flocks.

Protection Conferred by Infectious Coryza Vaccines Against Emergent Avibacterium paragallinarum Serovar C-1

Infectious coryza is an upper respiratory disease of chickens caused by Avibacterium paragallinarum. Outbreaks of infectious coryza caused by Av. paragallinarum serovar C-1 isolates in coryza-vaccinated flocks in Ecuador and Mexico have been reported. In the current study, the protection conferred by four commercially available, trivalent infectious coryza vaccines in chickens challenged with a serovar C-1 isolate from an apparent coryza vaccine failure in a layer flock in Mexico was evaluated. Only one infectious coryza vaccine provided a good protection level (83%) in vaccinated chickens. These results might explain the infectious coryza outbreaks in vaccinated flocks that have been observed in the field.

Genotyping, pathogenicity, and immunogenicity of Avibacterium paragallinarum serovar B-1 isolates from the Americas

The bacterium Avibacterium paragallinarum is the etiologic agent of infectious coryza of chickens. Among the nine Kume serovars currently recognized in this bacterium, serovar B-1 is a common serovar in the Americas. In the current study, serovar B-1 isolates from Ecuador (seven isolates), Mexico (seven isolates) and Panama (two isolates) were genotyped. In addition one Panamanian, one Ecuadorian, and two Mexican isolates were used in a vaccination-challenge trial in which the vaccine was based on the 2671 serovar B-1 reference strain. Genotyping by enterobacterial repetitive intergenic consensus-based PCR (ERIC-PCR) resulted in ten distinguishable ERIC patterns for the 16 isolates and the two reference strains of Av. paragallinarum included in the study. No ERIC patterns were shared among isolates of the three different countries. In the vaccination-challenge trial, one isolate from Panama showed a significantly lower virulence than did the three other isolates. In terms of cross-protection, chickens vaccinated with reference strain 2671 and challenged with an Ecuadorian strain showed 40% protection, a significantly lower protection than the homologous protection level. The other three field isolates gave a similar protection level to the homologous challenge.

An evaluation of serotyping of Avibacterium paragallinarum by use of a multiplex polymerase chain reaction

In the present study, the ability of a recently proposed multiplex polymerase chain reaction (mPCR) to determine the serogroups (A, B, and C) of Avibacterium paragallinarum was evaluated. A total of 12 reference strains and 69 field isolates of Av. paragallinarum from Ecuador, Mexico, Panama, and Peru were included in the study. With some exceptions (which were serotyped in the current study), all of the isolates and strains had been previously examined by 2 serotyping schemes (Page and Kume) or were the formal reference strains for the schemes. Three of 6 (50%) reference strains of serogroup A, 2 (100%) of serogroup B, and 1 of 4 (25%) reference strains of serogroup C were correctly serotyped by the mPCR. With the field isolates, the mPCR correctly recognized 16 of the 17 serogroup A isolates, 10 of the 12 serogroup B isolates, and 18 of the 37 serogroup C isolates. Overall, the specificity and sensitivity of the PCR test was as follows: 82.6% and 87.3% (serogroup A), 85.7% and 71.9% (serogroup B), and 46.3% and 100% (serogroup C). The poor performance of the mPCR in terms of recognition of serogroup C isolates (low sensitivity of 46.3%) and the relatively high level of uncertainty about the accuracy of the serogroup A and B results (specificity of 87.3% and 71.9%, respectively) means that the assay cannot be recommended as a replacement for conventional serotyping.