In the actual investigations the interaction between two bacterial pathogens Avibacterium paragallinarum and Gallibacterium anatis was studied. For this, chickens vaccinated with a commercial vaccine as well as non-vaccinated birds were infected either with A. paragallinarum or G. anatis or both, while negative control birds were left without vaccination and challenge (1). The applied readout system enabled to monitor the progression of disease parameters in live and sequentially killed birds (1, 2). As a result, clinical signs of infectious coryza were reproduced in non-vaccinated birds infected either with A. paragallinarum alone or with G. anatis. The severity of disease was higher in co-infected birds, resulting in mortality of some birds due to the infection. Postmortem examination revealed inflammation of sinus infraorbitalis and/or hemorrhagic follicles in non-vaccinated birds. Furthermore infiltration of inflammatory cells, thickening of mucosa and fibrinoheterophilic content were observed by histopathology in the affected birds. The microscopic lesion scores in sinus infraorbitalis and/or nasal turbinates harmonized with the severity of macroscopic findings. Direct plating revealed that A. paragallinarum could be re-isolated from respiratory organs, the frequency was, however, very limited in vaccinated birds. The localization of A. paragallinarum could be demonstrated in the nasal exudates by in situ hybridization. Likewise, G. anatis colonized systemically, including the respiratory and reproductive tracts. Bacterial quantification revealed that early multiplication of G. anatis is somewhat supported by the co-infection with A. paragallinarum but not vice versa. In contrast to vaccinated birds, antibody titers were provoked in non-vaccinated chickens following infection indicating lack of protection. In conclusion, the synergism between A. paragallinarum and G. anatis infection was demonstrated which led to potentiation of infectious coryza in non-vaccinated chickens.
References: (1) Paudel et al. (2017a), Avian Diseases 61:55-63; (2) Paudel et al. (2017b), Avian Diseases 61:335-340