Ornithobacterium rhinotracheale, a primary pathogen in broilers

Field strains of Ornithobacterium rhinotracheale were tested on their virul ence in different chicken breeds. Ornithobacterium rhinotracheale was able to induce lesions after aerosol challenge without a previous priming with v irus, and thus O. rhinotracheale was proven to be a primary pathogen. The v irulence of Dutch strains, isolated between 1995 and 1998, did not increase , but the Dutch isolates and a South African strain were more pathogenic co mpared with an American strain of O. rhinotracheale. White specific-parhoge n-free leghorns were less susceptible to O. rhinotracheale infection than b roilers, whereas there was no difference in susceptibility between commerci al broilers and specific-parhogen-free broilers.