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.

The Efficacy of a Trivalent Inactivated Salmonella Vaccine Combined with the Live S. Gallinarum 9R Vaccine in Young Layers after Experimental Infections with S. Enteritidis, S. Typhimurium, and S. Infantis.

Worldwide, poultry infections by Salmonella are the cause of significant economic losses, not only due to reduced production (due to fowl typhoid disease), but also considering the efforts and control measures that must be constantly applied, especially due to zoonotic serovars. Poultry is a common reservoir of Salmonella and its transmission into the food chain is a risk for humans. The vaccination of layers plays an important role in the overall efforts to prevent Salmonella infections. An inactivated trivalent vaccine was prepared with S. Enteritidis, S. Typhimurium, and S. Infantis strains. Infection trials were performed to evaluate the efficacy of three vaccination schedules using inactivated and live S. Gallinarum 9R vaccines. For this purpose, at week 5 of life, one subcutaneous dose of live S. Gallinarum 9R vaccine (1-5 × 107 CFU) was given to Groups 1 and 2. At weeks 8 and 11 of life, chickens were also vaccinated with one (Group 1) or two (Groups 2 and 3) intramuscular doses of the inactivated oil-adjuvant trivalent vaccine (1 × 108 CFU/dose of each antigen). Group 4 consisted of chickens that remained unvaccinated (control). At week 14 of life, the efficacy of the vaccination plans was evaluated in three separate inoculation trials with S. Enteritidis, S. Typhimurium, or S. Infantis. After vaccination with the inactivated vaccine, homologous antibody production was observed, and after challenge, a significant reduction in the faecal shedding, invasion, and colonization of S. Typhimurium and S. Infantis was achieved by all vaccination schedules, while the vaccination with at least one dose of the live S. Gallinarum 9R vaccine was necessary to obtain such a significant protection against S. Enteritidis infection.

Serotyping of Avibacterium paragallinarum isolates from Peru.

This study appears to represent the first serotyping study of 24 isolates of Avibacterium paragallinarum obtained from different regions of Peru during 1998-2008. All isolates were characterized as beta-nicotinamide adenine dinucleotide dependent. According to the Page scheme, modified by Blackall, it was found that eight isolates were classified as serogroup A, seven isolates as serogroup B, and five isolates as serogroup C, while four isolates could not be serotyped. Further serotyping, following the same scheme but using rabbit antiserum raised against Argentinean strains of the three serogroups, allowed allocation of these four unclassified isolates to serogroup B. These results suggest that some of the Peruvian B isolates appear to be similar to the previously described variant B isolates from Argentina. Therefore, inactivated vaccines used in Peru should include the three recognized serogroups (A, B, and C), with the addition of at least one of these variant B isolates. Cross-protection trials are needed to compare the protection conferred by vaccines containing traditional B serovar strains to the protection by experimental vaccines containing variant B serovar isolates from Peru.

Amplified 16S ribosomal DNA restriction analysis for identification of Avibacterium paragallinarum.

A molecular technique based on the restriction fragment length polymorphism of the 16S ribosomal genes amplified by a polymerase chain reaction (PCR), referred to as amplified 16S ribosomal DNA restriction analysis (ARDRA), was designed to identify 19 Avibacterium paragallinarum strains isolated from infraorbital sinus and nasal turbinate bone samples of broiler chickens, breeders, and laying hens from different regions of Peru. The 16S rDNA was amplified by PCR using a pair of bacterial universal primers and restriction analysis of 16S rDNA sequences was done to select endonucleases with the highest number of cutting points inside the 16S rDNA. The DNA patterns with DdeI and RsaI endonucleases were identical for the 19 A. paragallinarum strains, but differed from those obtained for Ornithobacterium rhinotracheale, a bacterium with a high genetic and phenotypic resemblance to A. paragallinarum, as well as from Escherichia coli, a bacterium associated with infectious coryza. The ARDRA method could prove to be valuable for molecular identification of A. paragallinarum, a microorganism implicated in respiratory diseases in commercial birds.