Imported parakeets harbor H9N2 influenza A viruses that are genetically closely related to those transmitted to humans in Hong Kong

In 1997 and 1998, H9N2 influenza A viruses were isolated from the respirato ry organs of Indian ring-necked parakeets (Psittacula Krameri manillensis) that had been imported from Pakistan to Japan. The two isolates were closel y related to each other (>99% as determined by nucleotide analysis of eight RNA segments), indicating that H9N2 viruses of the same lineage were maint ained in these birds for at least 1 year. The hemagglutinins and neuraminid ases of both isolates showed >97% nucleotide identity with those of H9N2 vi ruses isolated from humans in Hong Kong in 1999, while the six genes encodi ng internal proteins were >99% identical to the corresponding genes of H5N1 viruses recovered during the 1997 outbreak in Hong Kong. These results sug gest that the H9N2 parakeet viruses originating in Pakistan share an immedi ate ancestor with the H9N2 human viruses. Thus, influenza A viruses with th e potential to be transmitted directly to humans may be circulating in capt ive birds worldwide.