Avian-to-human transmission of H9N2 subtype influenza A viruses: Relationship between H9N2 and H5N1 human isolates

Abstract

In 1997, 18 cases of influenza in Hong Kong (bird flu) caused by a novel H5N1 (chicken) virus resulted in the deaths of six individuals and once again raised the specter of a potentially devastating influenza pandemic. Slaughter of the poultry in the live bird markets removed the source of infection and no further human cases of H5N1 infection have occurred. In March 1999, however, a new pandemic threat appeared when influenza A H9N2 viruses infected two children in Hong Kong. These two virus isolates are similar to an H9N2 virus isolated from a quail in Hong Kong in late 1997. Although differing in their surface hemagglutinin and neuraminidase components, a notable feature of these H9N2 viruses is that the six genes encoding the internal components of the virus are similar to those of the 1997 H5N1 human and avian isolates. This common feature emphasizes the apparent propensity of avian viruses with this genetic complement to infect humans and highlights the potential for the emergence of a novel human pathogen.

The evolution of human influenza viruses

“…The ability of avian internal genes to support e¤cient replication in human cells was also demonstrated by the severe infections by avian AH5N1 subtype viruses in Hong Kong in 1997; however, e¤cient person to person transmission did not ensue. The similarity between the six internal genes of the chicken H5N1 viruses and the quail H9N2 viruses, that caused human infections in 1999, (related by genetic reassortment) suggests that certain features of this genetic complement facilitate avian to human transmission (Lin et al 2000). Thus, domestic poultry also have a potential role in facilitating the emergence of a pandemic strain.…”

“…In addition, a WHO collaborating centre in Memphis, TN studying animal and avian in£uenza viruses provides an important interface for the rapid identi¢ca-tion of exotic human isolates. The principal objectives are: (i) the early detection and characterization of novel subtypes of human in£uenza A with the potential for causing pandemics, such as the recent cases of in£uenza AH5N1 and AH9N2 infection in Hong Kong (Claas et al 1998;Lin et al 2000) and (ii) the identi¢cation of new antigenic variants among currently circulating in£uenza A and B viruses in order to ensure that in£uenza vaccines contain components that re£ect the immunological characteristics of the prevalent viruses. The WHO has published formal recommendations for the compositions of in£uenza vaccines based on cumulative data since 1973.…”

Replication and transmission of mammalian-adapted H9 subtype influenza virus in pigs and quail

“…The first human isolates of H9N2 were recovered in 1999 in Hong Kong from two patients reporting mild respiratory symptoms (Peiris et al, 1999). Studies showed that these isolates were of the Eurasian G1-like sublineage (Lin et al, 2000). Subsequent isolates from sporadic human cases have been from the G1-and Y280-like lineages (Butt et al,to be more common and are associated with all sublineages (Cong et al, 2007;Rui-Hua et al, 2011;Xu et al, 2008).…”

Large-scale analysis of influenza A virus sequences reveals potential drug target sites of non-structural proteins

“…Apart from annually recurring epidemics, influenza A viruses, which infect avian and mammalian species, have been responsible for devastating pandemics killing at least 40 million people in 1918/1919 (Johnson & Mueller, 2002) and less serious pandemics in 1957 (Asian Influenza, H2N2), 1968 (Hong Kong Influenza, H3N2) and 1977 (Russian Influenza, H1N1) (Cox & Subbarao, 2000). Influenza pandemics seem to occur when a pathogenic avian-type virus acquires the capability of efficient human to human transmission (Horimoto & Kawaoka, 2005) which may occur due to mutations or reassortment of human and avian RNA segments (Lin et al, 2000). Currently, an avian H5N1 virus, which emerged in May 1997, is a threat (Claas et al, 1998;Subbarao et al, 1998) and was reported to have caused almost 250 human deaths up to 2009(World Health Organization, 2004.…”