| Infectious coryza,caused by Avibacterium paragallinarum ,is an acute respiratory disease of chickens. The most common clinical signs are nasal discharge,facial,swelling, lacrimation, anorexia, and diarrhea. The disease causes economic losses due to an increased number of culls and a marked (10% to more than 40%) drop in egg production, particularly on multi-age farms. The disease was first reported by Beach in 1920 and the causative organism was first isolated in 1931 by De Blieck. In China, the like disease was first reported in 1962 and bacteria were first isolated in Beijing by FengWenda. The disease occurs worldwide and causes serious economic losses.The Avibacterium paragallinarum previously was termed Haemophilus paragallinarum. The most widely used serotyping scheme for Avibacterium paragallinarum is the Page scheme, which recognizes three serovars: A, B, and C. As there is no cross-protection among Page serovars for the currently available whole cell inactivated vaccines, a knowledge of the serovars of the Avibacterium paragallinarum present in a region is of importance for effective vaccination. Isolates of serogroups A and C are all pathogenic, but different isolates of the same serogroup may have virulence diversity, and some isolates of serogroup B have been identified as non-virulent. Now there are still many questions about the identification of serogroups. For example, different serogroups cross–agglutinate, the bacteria auto agglutinate and variant serovars so on.The basic bionomics of the representative strains of three serotypes of Apg which are Hpg-8(A),CCM6075(B)and Hpg-668(C)were studied in this experiment. It included the observation of colonial morphology cultured on chicken broth plate, the thallus form by Gram staining, groping of growth regularity on chicken bouillon plate, demanding experiment of V factor, hemagglutination test, animal regression experiment and egg inoculation test. The results are to accord with the bionomics of Apg. In order to fast identify the serogroups of isolates, the homologous antisera had been gotten by utilizing the representative strains of the Avibacterium paragallinarum such as Hpg-8 (serotype A), CCM6075 (serotype B) and Hpg-668 (serotype C), and then A, B and C mono-specific antisera had been acquired by cross absorption test and all mono-specific antisera showed serotype-specificity. Further investigations indicated that the serotype of the six isolates of Avibacterium paragallinarum all belonged to serotype A identified by using the three mono-specific antiseraThe pathogenicity of Avibacterium paragallinarum is diverse between the birds of experimental infection and natural infection. To obtain the differences, so the birds were challenged by the two different methods in this study. One was imitated natural infection and another was injected via intrasinus with three strains of different serogroups of Avibacterium paragallinarum contained Hpg-8,CCM6075 and Hpg-668. During this study, a scoring system is introduced to record the clinical signs of the challenged birds of the two methods. The mean score of daily diseases of each strain can be calculated and plotted on a graph to obtain a dynamic curve, and then the total mean disease score of the whole period was calculated. The two methods of different strains can then be compared to each other, either graphically or the mean disease scores. At the end of the experiment, the bacteria were isolated and identified from the sinuses of all the birds. The final result indicated that the pathogenicities of injected via intrasinus were more serious and the ones of infected by natural route were more precise, the virulence of Hpg-8 appeared to be same as that of CCM6075 while more than that of Hpg-668.
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