| Influenza (flu) |
|---|
 |
H5N9 is a subtype of the species Influenza A virus (sometimes called bird flu virus). Wild aquatic birds are the primary host of the influenza A virus, which is enzootic (continually present) in many bird populations. [1] [2]
| Influenza (flu) |
|---|
| |
H5N9 is a subtype of the species Influenza A virus (sometimes called bird flu virus). Wild aquatic birds are the primary host of the influenza A virus, which is enzootic (continually present) in many bird populations. [1] [2]
A highly pathogenic strain of H5N9 caused an outbreak in 1966 in Ontario and Manitoba, Canada in turkeys, resulting in the slaughter of approximately 8,000 birds. [3] [4]
In 1999 an H5 influenza A virus was isolated from a mallard in the Netherlands. [5]
In 2008 An H5N9 virus was isolated from poultry in Aomori, Japan. [6]
In December 2015 an H5N9 virus infected a flock of 500 ducks raised for fatty liver production experienced a 5% mortality in Arrosès, France. [7]
In 2025 another highly pathogenic strain caused an outbreak in a duck farm in Merced County, California, forcing the culling of over 118,000 ducks. This strain may have arisen from recombination of H5N1 from the current 2020–2025 H5N1 outbreak and a subtype bearing N9. [8]
{{cite journal}}: Cite uses generic title (help)  | This infectious disease article is a stub. You can help Wikipedia by expanding it. |
Influenza A virus (IAV) is the only species of the genus Alphainfluenzavirus of the virus family Orthomyxoviridae. It is a pathogen with strains that infect birds and some mammals, as well as causing seasonal flu in humans. Mammals in which different strains of IAV circulate with sustained transmission are bats, pigs, horses and dogs; other mammals can occasionally become infected.
Avian influenza, also known as avian flu or bird flu, is a disease caused by the influenza A virus, which primarily affects birds but can sometimes affect mammals including humans. Wild aquatic birds are the primary host of the influenza A virus, which is enzootic in many bird populations.
Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus, which causes the disease avian influenza. It is enzootic in many bird populations, and also panzootic. A/H5N1 virus can also infect mammals that have been exposed to infected birds; in these cases, symptoms are frequently severe or fatal.
An influenza pandemic is an epidemic of an influenza virus that spreads across a large region and infects a large proportion of the population. There have been five major influenza pandemics in the last 140 years, with the 1918 flu pandemic being the most severe; this is estimated to have been responsible for the deaths of 50–100 million people. The 2009 swine flu pandemic resulted in under 300,000 deaths and is considered relatively mild. These pandemics occur irregularly.
The global spread of H5N1 influenza in birds is considered a significant pandemic threat. While other H5N1 influenza strains are known, they are significantly different on a genetic level from a highly pathogenic, emergent strain of H5N1, which was able to achieve hitherto unprecedented global spread in 2008. The H5N1 strain is a fast-mutating, highly pathogenic avian influenza virus (HPAI) found in multiple bird species. It is both epizootic and panzootic. Unless otherwise indicated, "H5N1" in this timeline refers to the 2008 highly pathogenic strain of H5N1.
Transmission and infection of H5N1 from infected avian sources to humans has been a concern since the first documented case of human infection in 1997, due to the global spread of H5N1 that constitutes a pandemic threat.
H5 N2 is a subtype of the species Influenzavirus A. The subtype infects a wide variety of birds, including chickens, ducks, turkeys, falcons, and ostriches. Affected birds usually do not appear ill, and the disease is often mild as avian influenza viral subtypes go. Some variants of the subtype are much more pathogenic than others, and outbreaks of "high-path" H5N2 result in the culling of thousands of birds in poultry farms from time to time. It appears that people who work with birds can be infected by the virus, but suffer hardly any noticeable health effects. Even people exposed to the highly pathogenic H5N2 variety that killed ostrich chicks in South Africa only seem to have developed conjunctivitis, or a perhaps a mild respiratory illness. There is no evidence of human-to-human spread of H5N2. On November 12, 2005 it was reported that a falcon was found to have H5N2. On June 5, 2024, the first confirmed human case of H5N2 was reported in Mexico.
Influenza A virus subtype H7N2 (A/H7N2) is a subtype of the species Influenza A virus. This subtype is one of several sometimes called bird flu virus. H7N2 is considered a low pathogenicity avian influenza (LPAI) virus. With this in mind, H5 & H7 influenza viruses can re-assort into the Highly Pathogenic variant if conditions are favorable.
The genetic structure of H5N1, a highly pathogenic avian influenza virus, is characterized by a segmented RNA genome consisting of eight gene segments that encode for various viral proteins essential for replication, host adaptation, and immune evasion.
The global spread of H5N1 in birds is considered a significant pandemic threat.
Fujian flu refers to flu caused by either a Fujian human flu strain of the H3N2 subtype of the Influenza A virus or a Fujian bird flu strain of the H5N1 subtype of the Influenza A virus. These strains are named after Fujian, a coastal province in Southeast China.
H5N1 influenza virus is a type of influenza A virus which mostly infects birds. H5N1 flu is a concern due to the fact that its global spread may constitute a pandemic threat. The yardstick for human mortality from H5N1 is the case-fatality rate (CFR); the ratio of the number of confirmed human deaths resulting from infection of H5N1 to the number of those confirmed cases of infection with the virus. For example, if there are 100 confirmed cases of a disease and 50 die as a consequence, then the CFR is 50%. The case fatality rate does not take into account cases of a disease which are unconfirmed or undiagnosed, perhaps because symptoms were mild and unremarkable or because of a lack of diagnostic facilities. The Infection Fatality Rate (IFR) is adjusted to allow for undiagnosed cases.
A panzootic is an epizootic that spreads across a large region, or even worldwide. The equivalent in human populations is called a pandemic.
The global spread of H5N1 in birds is considered a significant pandemic threat.
Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms begin one to four days after exposure to the virus and last for about two to eight days. Diarrhea and vomiting can occur, particularly in children. Influenza may progress to pneumonia from the virus or a subsequent bacterial infection. Other complications include acute respiratory distress syndrome, meningitis, encephalitis, and worsening of pre-existing health problems such as asthma and cardiovascular disease.
A H5N1 vaccine is an influenza vaccine intended to provide immunization to influenza A virus subtype H5N1.
Influenza A virus subtype H7N9 (A/H7N9) is a subtype of the influenza A virus, which causes influenza (flu), predominantly in birds. It is enzootic in many bird populations. The virus can spread rapidly through poultry flocks and among wild birds; it can also infect humans that have been exposed to infected birds.
Cats with avian influenza exhibit symptoms that can result in death. The avian influenza viruses cats may get include H5N1 or H7N2, notable pathogenic subtypes of the virus. In order to get the virus, a cat would need to be in contact with infected waterfowl, poultry, or uncooked poultry. Two of the main organs that the virus affects are the lungs and liver.
Since 2020, outbreaks of avian influenza subtype H5N1 have been occurring, with cases reported from every continent except Australia as of January 2025. Some species of wild aquatic birds act as natural asymptomatic carriers of a large variety of influenza A viruses, which can infect poultry, other bird species, mammals and humans if they come into close contact with infected feces or contaminated material, or by eating infected birds. In late 2023, H5N1 was discovered in the Antarctic for the first time, raising fears of imminent spread throughout the region, potentially leading to a "catastrophic breeding failure" among animals that had not previously been exposed to avian influenza viruses. The main virus involved in the global outbreak is as H5N1 clade 2.3.4.4b, genetic diversification of which with other clades has seen an evolution in the ability to cause significant outbreaks in a broader range of species, mammals included.