H9N2 subtype influenza A viruses in poultry in Pakistan are closely related to the H9N2 viruses responsible for human infection in Hong Kong

Following the outbreak of H5N1 "bird flu" in Hong Kong in 1997 the isolatio n of H9N2 subtype viruses from patients in southern China and Hong Kong SAR once again raised the spectre of a possible influenza pandemic. H9N2 virus es have recently been responsible for disease in poultry in various parts o f the world and preliminary studies of the H9 haemagglutinin (HA) genes of viruses isolated during 1998 and 1999 in Germany, Iran, Pakistan, and Saudi Arabia showed a close relationship to the HA genes of the viruses that inf ected two children in Hong Kong SAR. Analysis of the complete genome of a P akistan isolate, A/chicken/Pakistan/2/99, showed that it is closely related in all eight genes (97-99% homology) to the human H9N2 isolates and furthe rmore that the six genes encoding internal components of the virus are simi lar to the corresponding genes of the H5N1 viruses that caused 6 (out of 18 ) fatal cases of human infection. Thus H9N2 viruses similar to those that c aused human infections in Hong Kong are circulating more widely in other pa rts of the world. Whether or not these H9N2 viruses also have features that facilitate avian-to-human transmission is not known. Since avian H9N2 viru ses are currently perceived to represent a significant threat to human heal th it is important to determine whether or not viruses of this subtype circ ulating in poultry in various parts of the world have the potential to infe ct people. (C) 2000 Academic Press.