The development of a molecular serotyping system and an investigation into the presence of prophages in Avibacterium paragallinarum serogroups
Avibacterium paragallinarum is an avian pathogen that causes the upper respiratory disease Infectious coryza (IC) in chickens. This disease has the ability to cause vast economic losses due to a decrease in egg production. To date the factors contributing to pathogenicity, immunogenicity and serotyping are still not clearly understood. Vaccine failures are a major problem that occurs due to no or poor cross-protection occurring especially between the C-serovars of A. paragallinarum. This problem will be overcome by having a more accurate serotyping technique available for the diagnosis of IC. Therefore one of the aims of this study was the development of a molecular serotyping technique, where a serotyping PCR was developed which distinguished between the Modesto (C-2) and SA-3 (C-3) A. paragallinarum isolates which is the major cause of IC in South Africa. Reported in a recently published article was the presence of a HP2-like and Mu-like phage within the genome of the Modesto (C-2) strain of A. paragallinarum. Therefore another major question addressed during this study was whether there are prophage genes present in all of the reference isolates as well as in field isolates of A. paragallinarum and what the effect of these phages might be on the virulence and pathogenicity of these isolates. Phage genes that are important during lysogeny were selected and screened for by means of PCR. From the results it was able to determine that some of these genes are present in some of these isolates but no discernible patterns were detected in terms of the effect on pathogenicity. Therefore future studies will be conducted to mainly focus on the effect these phages might have on the virulence and pathogenicity as well as whether these phages are responsible for the occurrence of different A. paragallinarum serovars.