H5N1 avian influenza virus: an overview. Address for correspondence. Avian influenza virus H5N1 emerged in Hong Kong in , causing severe human disease. In recent years, several outbreaks have been reported in different parts of Asia, Europe and Africa, raising concerns of dissemination of a new and highly lethal influenza pandemic.
UNDERSTANDING AVIAN INFLUENZA
Asian Lineage Avian Influenza A(H7N9) Virus | Avian Influenza (Flu)
Pandemic influenza virus has its origins in avian influenza viruses. The highly pathogenic avian influenza virus subtype H5N1 is already panzootic in poultry, with attendant economic consequences. It continues to cross species barriers to infect humans and other mammals, often with fatal outcomes. Therefore, H5N1 virus has rightly received attention as a potential pandemic threat. However, it is noted that the pandemics of and did not arise from highly pathogenic influenza viruses, and the next pandemic may well arise from a low-pathogenicity virus. The rationale for particular concern about an H5N1 pandemic is not its inevitability but its potential severity. An H5N1 pandemic is an event of low probability but one of high human health impact and poses a predicament for public health.
Avian influenza H5N1 infection in humans: urgent need to eliminate the animal reservoir - update 5
The global spread of highly pathogenic H5N1 influenza in birds is considered a significant pandemic threat. While other H5N1 influenza  strains are known, they are significantly different from a current, highly pathogenic H5N1 strain on a genetic level, making the global spread of this new strain unprecedented. It is both epizootic an epidemic in non-humans and panzootic a disease affecting animals of many species especially over a wide area.
This was followed by further outbreaks in HKSAR in poultry only from to early Sims et al , a and poultry and captive wild birds in Ellis et al , From onwards, infection and disease spread widely to three continents, initially through East and Southeast Asia in , and then into southern Russia, the Middle East, Europe, Africa and south Asia in The precise events that led to broad transborder spread of these viruses are not known, but among the likely contributory factors are the changes that allowed the H5N1 HPAI viruses to multiply subclinically in ducks see section 3. The presence of high quantities of virus in domestic ducks in a system where live poultry are moved long distances and sold in live-bird markets Li et al , without being tested for infection would facilitate spread of infection within, and perhaps in some cases, between countries. The adaptation to ducks may also have favoured subsequent spread of H5N1 by wild Anatidae Gilbert et al , a; Sturm-Ramirez et al ,