A detailed study on histopathological lesions induced by two C. psittaci outer membrane protein A (ompA) genotype B strains (10/423 and 10/525) and one genotype D strain (10/298) in experimentally infected (aerosol) specific pathogen free (SPF) chickens was performed. The strains were derived from Belgian and French commercially raised broilers with pneumonia. Both genotype B and D strains induced conjunctivitis, rhinitis, sinusitis, tracheitis, bronchitis, pneumonitis, airsacculitis, splenitis, hepatitis, nephritis, and enteritis in sequentially (days 2 to 34 post infection) euthanized chickens. Inflammation of the ovaries was only observed in genotype D infected chickens. Overall, the genotype D strain caused more severe gross and histopathological lesions and mortality (54.5%) early upon infection. The genotype D strain seemed to replicate faster as severity of the lesions increased more quickly. C. psittaci is a primary pathogen in chickens, and efficient monitoring and control of this emerging zoonotic pathogen is urgently needed.
