What is avian influenza H5N1?
While only two influenza A subtypes currently circulate in humans, influenza A viruses of all subtypes can infect birds. Of particular concern to public health authorities is the highly pathogenic avian influenza A(H5N1) virus ('bird flu') which causes devastating disease in domestic poultry flocks. H5N1 viruses spread rapidly at a local level amongst poultry and their global transmission has been facilitated by international trade in poultry and poultry products and, to some extent, by migratory birds. Most known cases of human infection with these viruses have occurred in people who have had close contact with infected birds. To date cases of human-to-human transmission have been extremely rare.
What is the concern about H5N1 influenza?
Public health authorities are concerned that an H5N1 virus may undergo changes that allow it to spread easily between humans, causing a pandemic. Furthermore, in cases where people have been infected by the H5N1 virus, the disease has been particularly severe and aggressive. If the new virus retained the properties of current H5N1 viruses that cause severe disease in humans, the mortality rate would be high.
What is being done to prepare for a H5N1 influenza pandemic?
WHO continues to monitor human cases of H5N1 infection throughout the world, as well as avian outbreaks. WHO Collaborating Centres and other laboratories in the WHO Global Influenza Surveillance and Response System (GISRS) collect and characterise H5N1 viruses isolated from infected humans and birds, and the WHO reports regularly on the availability of suitable H5N1 vaccine candidates that correspond to the different groups (clades and subclades) of H5N1 viruses circulating in different parts of the world. A number of research institutions and vaccine manufacturers are developing vaccines for H5N1 influenza and taking them into clinical trials. Many individual governments also have public health emergency plans should a pandemic occur. In Australia, local bird populations continue to be monitored – to date, highly pathogenic H5N1 viruses have not been found in Australian avian populations.
What is avian influenza H7N9?
In 2013 a novel avian influenza A(H7N9) virus emerged in China that has infected humans with a high fatality rate. Unlike highly pathogenic avian influenza (H5N1), avian influenza A(H7N9) does not kill poultry and so is much harder to detect in the environment than H5N1 viruses as it must be detected by laboratory testing. Most known cases of human infection with these viruses have occurred in people who have had close contact with infected birds or contaminated environments. To date, there has only been rare evidence of human-to-human transmission. Currently this virus has been largely confined to China and circulates most prominently from December to April each year. WHO continues to monitor human cases of H7N9, as well as working with animal health organisations to determine the source of the infection and also support the development of possible vaccines for H7N9 influenza.
Are there other types of non-human influenzas?
In addition to avian influenzas, influenza viruses can also infect other animals. While birds can be infected by most of the known influenza A subtypes, a smaller number of subtypes are also known to infect pigs, horses, dogs and other species. Recently bats have been found to have influenza-like viruses. Historically there have been no recorded instances of natural transmission from horses or dogs to humans, but transmission from pigs to humans does occur from time to time. The pandemic H1N1 influenza strain that emerged in 2009, commonly referred to as the 'swine flu', was the result of a series of genetic shuffling events between swine, avian and human influenza viruses that had occurred over many years, ultimately producing a virus that is now transmitted readily between people.
More information:
World Health Organisation information about Avian Influenza
Australian Government Department of Health
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