[Differentiation of Haemophilus strains isolated from chickens. III. Pathogenicity tests in chickens]

Pathogenicity tests of 6 isolates of the Haemophilus-group I (H. paragallinarum) and 8 isolates of the Haemophilus-group II isolated from chickens in the Federal German Republic and one strain of H. parainfluenzae isolated from man were carried out in 6-week old SPF-chickens. Infectious coryza (Coryza contagiosa gallinarum) could be produced in chickens with all strains of group I after experimental inoculation and by contact exposure. At necropsy 3 weeks post inoculation (p.i.) organisms of group I were recovered from the sinus and nose of chickens with and without symptoms. The Haemophilus-bacteria however could not be reisolated from lungs and air sacs. No clinical and pathological symptoms were observed in chickens inoculated with isolates : of group II. In another trial these strains were not pathogenic even though chickens were pre-infected with an attenuated infectious bronchitis virus (IBV; Massachusetts type). However, these Haemophilus-bacteria were able to spread from inoculated to non-inoculated chickens by direct contact, and airborne transmission over a distance of 1.5 metres also occurred. Haemophilus organisms of group II were reisolated up to the end of the observation period of 35 days p.i. from the nose, sinus and trachea, but not from the lungs and air sacs. In chickens pre-infected with Mycoplasma gallisepticum and IBV, one strain of group I and of group II could be recovered from the lower respiratory tract (lungs and air sac exudate). Sera from chickens inoculated with the group II strain contained agglutinins to Haemophilus and the titre increased in 8 out of 10 chickens. Sera from chickens without pre-infection with both M. gallisepticum and IBV showed no antibody response to the inoculated group II Haemophilus strain. The H. parainfluenzae strain was non pathogenic and could not be isolated from the respiratory tract of the inoculated chickens at 48 hours p.i.