Evaluation of two experimental infection models for Avibacterium paragallinarum.

The clinical symptoms of infectious coryza are multiple and include nasal discharge, facial swelling, lacrimation, and anorexia. In general, the disease is not fatal to chicken; so, in experiments where animals are infected with Avibacterium paragallinarum, there have been debates about conducting the challenge model and evaluating the clinical signs. In this experiment, 150 chickens, aged 30 days, were randomly divided into different groups. Some groups were infected with the 'in-contact' challenge model and others with the artificial intrasinus-injection-route model. The bacterial isolates used were three field isolates of different serogroups of A. paragallinarum, including Hpg-8 (Page serovar A), CCM6075 (Page serovar B) and Hpg-668 (Page serovar C). During this study, a scoring system was used to record the clinical signs of the infected birds and evaluate the pathogenic diversity of the two models. The final results indicated that the 'in-contact' challenge model of the three isolates showed a more reliable representation of the natural infection under field conditions than the artificial intrasinus-injection-route model. Thus, on carrying out animal experiments, the effect of 'in-contact' challenge model is more accurate than the artificial intrasinus-injection-route model.