ASSESSMENT OF THE ABILITY OF RATITE-ORIGIN INFLUENZA-VIRUSES TO INFECT AND PRODUCE DISEASE IN RHEAS AND CHICKENS

Pathobiologic characteristics were determined for three mildly pathoge nic (MP) ratite-origin avian influenza viruses (AIVs). Ratite-origin A IVs produced respiratory disease in rheas, and virus was reisolated fr om oropharyngeal and cloacal swabs on days 2-6 postinoculation. Inocul ation of two ratite-origin AIVs in the upper respiratory tract. of chi ckens resulted in viral infections, but the mean chicken infectious do se (CID50) for A/emu/Texas/39924/93 (H5N2) (Emu/Texas) virus was 500-f old lower than the CID50 for the A/rhea/North Carolina/39482/93 (H7N1) virus. In ovo and in vivo passage of the MP parent Emu/Texas isolate resulted in emergence of a highly pathogenic (HP) variant that had hig h plaquing efficiency in chicken embryo fibroblast cultures and was hi ghly lethal in chicken pathotyping tests. This variant virus produced gross lesions in chickens similar to those reported for other HP AIVs. These findings demonstrated that ratite-origin AIVs can produce signi ficant clinical disease in rheas and have a realistic potential for in terspecies transmission to domestic poultry Furthermore, HP variants c an emerge from MP H5 ratite-origin AIVs if introduced and allowed to c irculate in chicken populations.