Reemerging H5N1 Influenza Viruses in Hong Kong in 2002 Are Highly Pathogenic to Ducks

Abstract

Waterfowl are the natural reservoir of all influenza A viruses, which are usually nonpathogenic in wild aquatic birds. However, in late 2002, outbreaks of highly pathogenic H5N1 influenza virus caused deaths among wild migratory birds and resident waterfowl, including ducks, in two Hong Kong parks. In February 2003, an avian H5N1 virus closely related to one of these viruses was isolated from two humans with acute respiratory distress, one of whom died. Antigenic analysis of the new avian isolates showed a reactivity pattern different from that of H5N1 viruses isolated in 1997 and 2001. This finding suggests that significant antigenic variation has recently occurred among H5N1 viruses. We inoculated mallards with antigenically different H5N1 influenza viruses isolated between 1997 and 2003. The new 2002 avian isolates caused systemic infection in the ducks, with high virus titers and pathology in multiple organs, particularly the brain. Ducks developed acute disease, including severe neurological dysfunction and death. Virus was also isolated at high titers from the birds' drinking water and from contact birds, demonstrating efficient transmission. In contrast, H5N1 isolates from 1997 and 2001 were not consistently transmitted efficiently among ducks and did not cause significant disease. Despite a high level of genomic homology, the human isolate showed striking biological differences from its avian homologue in a duck model. This is the first reported case of lethal influenza virus infection in wild aquatic birds since 1961.

The effect of age on the pathogenesis of a highly pathogenic avian influenza (HPAI) H5N1 virus in Pekin ducks (Anas platyrhynchos) infected experimentally

“…Prior to 2002, the only documented infection of significant numbers of wild birds infected with an HPAI virus occurred in common terns ( Sterna hirundo ) in South Africa, in 1961 – when large numbers died as a result of infection with A/tern/South Africa/1961 (H5N3) 1 . However, an H5N1 HPAI variant emerged in Penfold and Kowloon waterfowl parks, Hong Kong in December 2002 that, although genetically related to the progenitor isolates A/goose/Guangdong/1/1996 (H5N1) and A/Hong Kong/156/1997 (H5N1), showed increased lethality for various wild waterfowl, including geese, ducks and swans 2 . Although sporadic outbreaks in wild‐bird and poultry populations, with associated mortality because of this H5N1 HPAI virus were reported between 2002 and 2005, a virus representing a distinct sub‐clade of this Asian‐lineage was identified on Qinghai Lake, China in 2005, which displayed higher lethality and transmissibility for a wide range of wild birds 3 .…”

Geostatistical visualisation and spatial statistics for evaluation of the dispersion of epidemic highly pathogenic avian influenza subtype H5N1

“…In the recent outbreaks of HPAI subtype H5N1 in waterfowl, the virus has been more prevalent in respiratory tissue than intestinal tissue [26]. Persistence of this strain in migratory waterfowl (or even the environment) could be due to the prolonged shedding of virus in ducks, as well as changes in the virus that allows transmission via respiratory routes [26]. Prior to the recent HPAI subtype H5N1 outbreaks in ducks, host adaptation and lack of virulence in aquatic birds was cited as the reason for persistence in these species [32].…”

“…Prior to the recent HPAI subtype H5N1 outbreaks in ducks, host adaptation and lack of virulence in aquatic birds was cited as the reason for persistence in these species [32]. Recent studies in China have shown that viral lineages, established in poultry, have infected ducks [15,26].…”

H5N1 highly pathogenic avian influenza virus isolated from conjunctiva of a whooper swan with neurological signs

“…However, in 2002, outbreaks of H5N1 highly pathogenic AIV (HPAIV) started in Hong Kong, where deaths of many wild birds were recorded [5,17]. Since then, Japan has experienced three H5N1 outbreaks.…”