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92-581: 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 (maintained in the population) 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. A/H7N9 virus is shed in the saliva, mucus, and feces of infected birds; other infected animals may shed bird flu viruses in respiratory secretions and other body fluids. Symptoms of A/H7N9 influenza vary according to both

184-420: A cold , although usually more severe and less likely to include a runny nose . The onset of symptoms is sudden, and initial symptoms are predominately non-specific: a sudden fever; muscle aches; cough; fatigue; sore throat; headache; difficulty sleeping; loss of appetite; diarrhoea or abdominal pain; nausea and vomiting. Humans can rarely become infected with strains of avian or swine influenza , usually as

276-475: A zoonotic event. As of June 2024, there is concern about two subtypes of avian influenza which are circulating in wild bird populations worldwide, A/H5N1 and A/H7N9 . Both of these have potential to devastate poultry stocks, and both have jumped to humans with relatively high case fatality rates . A/H5N1 in particular has infected a wide range of mammals and may be adapting to mammalian hosts. The Global Influenza Surveillance and Response System (GISRS)

368-400: A zoonotic event. It is thought that all influenza A viruses causing outbreaks or pandemics among humans since the 1900s originated from strains circulating in wild aquatic birds through reassortment with other influenza strains. It is possible (though not certain) that pigs may act as an intermediate host for reassortment. The Global Influenza Surveillance and Response System (GISRS)

460-472: A Spanish mink farm showed evidence of being the first recorded case of mammal-to-mammal transmission, with 4 percent of the farm's mink population dying from H5N1-related haemorrhagic pneumonia. This coincided with H5N1 detections in the area among gulls and other seabirds, which are the presumed source of the outbreak. A mass Caspian seal die-off in December 2022, with 700 infected seals found dead along

552-593: A common ancestor around 8,000 years ago. Outbreaks of influenza-like disease can be found throughout recorded history. The first probable record is by Hippocrates in 142 BCE. The historian Fujikawa listed 46 epidemics of flu-like illness in Japan between 862 and 1868. In Europe and the Americas, a number of epidemics were recorded through the Middle Ages and up to the end of the 19th century. In 1918-1919 came

644-428: A dry, hacking cough, depression, loss of appetite and weakness. EI is caused by two subtypes of influenza A viruses: H7N7 and H3N8, which have evolved from avian influenza A viruses. Most animals infected with canine influenza A will show symptoms such as coughing, runny nose, fever, lethargy, eye discharge, and a reduced appetite lasting anywhere from 2–3 weeks. There are two different influenza A dog flu viruses: one

736-468: A few people. All subtypes of avian Influenza A have potential to cross the species barrier, with H5N1 and H7N9 considered the biggest threats. In order to avoid infection, the general public are advised to avoid contact with sick birds or potentially contaminated material such as carcasses or feces. People working with birds, such as conservationists or poultry workers, are advised to wear appropriate personal protection equipment. Other animals –

828-546: A few people. All subtypes of avian Influenza A have potential to cross the species barrier, with H5N1 and H7N9 considered the biggest threats. In order to avoid infection, the general public are advised to avoid contact with sick birds or potentially contaminated material such as carcasses or feces. People working with birds, such as conservationists or poultry workers, are advised to wear appropriate personal protection equipment. The avian influenza hemagglutinin prefers to bind to alpha-2,3 sialic acid receptors, while

920-412: A human-adapted strain. H7N9 is a subtype of Influenza A virus. Like all subtypes it is an enveloped negative-sense RNA virus , with a segmented genome. Influenza viruses have a relatively high mutation rate that is characteristic of RNA viruses . The segmentation of its genome facilitates genetic recombination by reassortment in hosts infected with two different strains of influenza viruses at

1012-406: A large reservoir in wild waterfowl, which can infect the respiratory and gastrointestinal tract without affecting the health of the host. They can then be carried by the bird over large distances especially during annual migration. Infected birds can shed avian influenza A viruses in their saliva, nasal secretions, and feces; susceptible birds become infected when they have contact with the virus as it

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1104-462: A layer between the nucleoprotein and the envelope, called the capsid . Envelope - The viral envelope consists of a lipid bilayer derived from the host cell. Two viral proteins; hemagglutinin (HA) and neuraminidase (NA), are inserted into the envelope and are exposed as spikes on the surface of the virion. Both proteins are antigenic ; a host's immune system can react to them and produce antibodies in response. The M2 protein forms an ion channel in

1196-669: A lipid envelope. The virus particle (also called the virion ) is 80–120 nanometers in diameter such that the smallest virions adopt an elliptical shape; larger virions have a filamentous shape. Core - The central core of the virion contains the viral RNA genome, which is made of eight separate segments. The nucleoprotein (NP) coats the viral RNA to form a ribonucleoprotein that assumes a helical (spiral) configuration. Three large proteins (PB 1 , PB 2 , and PA), which are responsible for RNA transcription and replication, are bound to each segment of viral RNP. Capsid - The matrix protein M1 forms

1288-404: A mechanism called cap-snatching . It consists in the hijacking and cleavage of host capped pre-mRNAs . Host cell mRNA is cleaved near the cap to yield a primer for the transcription of positive-sense viral mRNA using the negative-sense viral RNA as a template. The host cell then transports the viral mRNA into the cytoplasm where ribosomes manufacture the viral proteins. Replication of

1380-593: A pandemic in 2009. Because of its close resemblance to some strains circulating in pigs, this became known as " Swine flu " Influenza A virus continues to circulate and evolve in birds and pigs. Almost all possible combinations of H (1 thru 16) and N (1 thru 11) have been isolated from wild birds. As of June 2024, two particularly virulent IAV strains - H5N1 and H7N9 - are predominant in wild bird populations. These frequently cause outbreaks in domestic poultry, with occasional spillover infections in humans who are in close contact with poultry. Influenza viruses have

1472-467: A relatively high mutation rate that is characteristic of RNA viruses . The segmentation of the influenza A virus genome facilitates genetic recombination by segment reassortment in hosts who become infected with two different strains of influenza viruses at the same time. With reassortment between strains, an avian strain which does not affect humans may acquire characteristics from a different strain which enable it to infect and pass between humans -

1564-407: A result of close contact with infected animals or contaminated material; symptoms generally resemble seasonal flu but occasionally can be severe including death. Some species of wild aquatic birds act as natural asymptomatic carriers of a large variety of influenza A viruses, which they can spread over large distances in their annual migration. Symptoms of avian influenza vary according to both

1656-474: A result of close contact with infected animals; symptoms range from mild to severe including death. Bird-adapted strains of the virus can be asymptomatic in some aquatic birds but lethal if they spread to other species, such as chickens. IAV disease in poultry can be can be prevented by vaccination, however biosecurity control measures are preferred. In humans, seasonal influenza can be treated in its early stages with antiviral medicines. A global network,

1748-400: A segmented genome. Through a combination of mutation and genetic reassortment the virus can evolve to acquire new characteristics, enabling it to evade host immunity and occasionally to jump from one species of host to another. Subtypes of IAV are defined by the combination of the antigenic H and N proteins in the viral envelope ; for example, " H1N1 " designates an IAV subtype that has

1840-403: A significant drop in egg production, and sudden death. In mammals, including humans, A/H5N1 influenza (whether LPAI or HPAI) is rare. Symptoms of infection vary from mild to severe, including fever, diarrhoea, and cough. Human infections with A/H5N1 virus have been reported in 23 countries since 1997, resulting in severe pneumonia and death in about 50% of cases. Between 2003 and November 2024,

1932-470: A significant drop in egg production, and sudden death. In mammals, including humans, A/H7N9 influenza (whether LPAI or HPAI) is rare; it can usually be traced to close contact with infected poultry or contaminated material such as feces. Symptoms of infection vary from mild to severe, including fever, diarrhoea, and cough; the disease can often be fatal. The A/H7N9 virus is considered to be enzootic (continually present) in wild aquatic birds, which may carry

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2024-688: A special issue of the journal Science devoted to H5N1. The papers by Fouchier and Kawaoka conclude that it is entirely possible that a natural chain of mutations could lead to an H5N1 virus acquiring the capability of airborne transmission between mammals, and that a H5N1 influenza pandemic would not be impossible. In May 2013, it was reported that scientists at the Harbin Veterinary Research Institute in Harbin , China, had created H5N1 strains which passed between guinea pigs . In response to Fouchier and Kawaoka's work,

2116-399: A specific isolate of virus, researchers use the internationally accepted Influenza virus nomenclature, which describes, among other things, the species of animal from which the virus was isolated, and the place and year of collection. For example, A/chicken/Nakorn-Patom/Thailand/CU-K2/04(H5N1) : Other examples include: A/duck/Hong Kong/308/78(H5N3), and A/shoveler/Egypt/03(H5N2). H5N1

2208-644: A type-1 hemagglutinin (H) protein and a type-1 neuraminidase (N) protein. Almost all possible combinations of H (1 thru 16) and N (1 thru 11) have been isolated from wild birds. Further variations exist within the subtypes and can lead to very significant differences in the virus's ability to infect and cause disease, as well as to the severity of symptoms. Symptoms of human seasonal flu usually include fever, cough, sore throat , muscle aches , conjunctivitis and, in severe cases, breathing problems and pneumonia that may be fatal. Humans can rarely become infected with strains of avian or swine influenza , usually as

2300-491: A type-5 hemagglutinin (H) protein and a type-1 neuraminidase (N) protein. Further variations exist within the subtypes and can lead to very significant differences in the virus's behavior. By definition, the subtyping scheme only takes into account the two outer proteins, not the at least 8 proteins internal to the virus. Almost all possible combinations of H (1 thru 16) and N (1 thru 11) have been isolated from wild birds. H17 and H18 have only been discovered in bats. Due to

2392-458: A wide range of other animals have been affected by avian flu, generally due to eating birds which had been infected. There have been instances where transmission of the disease between mammals, including seals and cows, may have occurred. Many more outbreaks are recorded, in almost every country in the world, affecting both wild birds and poultry, with occasional spillover events infecting humans. In October 2022 an outbreak of H5N1 on

2484-576: Is a global network of laboratories that monitor the spread of influenza with the aim to provide the World Health Organization with influenza control information and to inform vaccine development. Several millions of specimens are tested by the GISRS network annually through a network of laboratories in 127 countries. As well as human viruses, GISRS monitors avian, swine, and other potentially zoonotic influenza viruses. Flu season

2576-488: Is a global network of laboratories that monitor the spread of influenza with the aim to provide the World Health Organization with influenza control information and to inform vaccine development. Several millions of specimens are tested by the GISRS network annually through a network of laboratories in 127 countries. GISRS monitors avian, swine, and other potentially zoonotic influenza viruses as well as human viruses. Birds – Influenza A viruses of various subtypes have

2668-552: Is a mandatory vaccination requirement since 2017; the vaccine is bivalent or trivalent, targeting the H5 and H7 subtypes of influenza A virus. It is manufactured using recombinant influenza virus. In the event of an outbreak of human H5N1, the main antiviral drugs recommended are neuraminidase inhibitors , such as zanamivir (Relenza) and oseltamivir (Tamiflu) . These drugs can reduce the severity of symptoms if taken soon after infection and can also be taken as prophylaxis to decrease

2760-415: Is a subtype of Influenza A virus. Like all subtypes it is an enveloped negative-sense RNA virus , with a segmented genome . Subtypes of IAV are defined by the combination of the antigenic hemagglutinin and neuraminidase proteins in the viral envelope . "H5N1" designates an IAV subtype that has a type 5 hemagglutinin (H) protein and a type-1 neuraminidase (N) protein. Further variations exist within

2852-455: Is an H3N8 virus and the other is an H3N2 virus. The H3N8 strain has evolved from an equine influenza avian virus which has adapted to sustained transmission among dogs. The H3N2 strain is derived from an avian influenza which jumped to dogs in 2004 in either Korea or China. It is likely that the virus persists in both animal shelters and kennels, as well as in farms where dogs are raised for meat production. The first bat flu virus, IAV(H17N10),

Influenza A virus subtype H7N9 - Misplaced Pages Continue

2944-588: Is an annually recurring time period characterized by the prevalence of an outbreak of influenza , caused either by Influenza A or by Influenza B . The season occurs during the cold half of the year in temperate regions; November through February in the northern hemisphere and May to October in the southern hemisphere. Flu seasons also exist in the tropics and subtropics , with variability from region to region. Annually, about 3 to 5 million cases of severe illness and 290,000 to 650,000 deaths from seasonal flu occur worldwide. There are several possible reasons for

3036-676: Is based solely on the effect on chickens - a virus strain is highly pathogenic avian influenza ( HPAI ) if 75% or more of chickens die after being deliberately infected with it, or if it is genetically similar to such a strain. The alternative classification is low pathogenic avian influenza (LPAI). Classification of a virus strain as either LPAI or HPAI is based on the severity of symptoms in domestic chickens and does not predict severity of symptoms in other species. Chickens infected with LPAI display mild symptoms or are asymptomatic , whereas HPAI causes serious breathing difficulties, significant drop in egg production, and sudden death. Since 2006,

3128-509: Is based solely on the effect on chickens – a virus strain is highly pathogenic avian influenza (HPAI) if 75% or more of chickens die after being deliberately infected with it. The alternative classification is low pathogenic avian influenza (LPAI). This classification system has since been modified to take into account the structure of the virus' haemagglutinin protein. Other species of birds, especially water birds, can become infected with HPAI virus without experiencing severe symptoms and can spread

3220-430: Is characteristic of RNA viruses . The segmentation of the influenza A virus genome facilitates genetic recombination by segment reassortment in hosts who become infected with two different strains of influenza viruses at the same time. With reassortment between strains, an avian strain which does not affect humans may acquire characteristics from a different strain which enable it to infect and pass between humans –

3312-511: Is concern about two subtypes of avian influenza which are circulating in wild bird populations worldwide, H5N1 and H7N9 . Both of these have potential to devastate poultry stocks, and both have jumped to humans with relatively high case fatality rates . H5N1 in particular has infected a wide range of mammals and may be adapting to mammalian hosts. As of June 2024, the influenza viruses which circulate widely in humans are IAV subtypes H1N1 and H3N2, together with Influenza B. Annual vaccination

3404-680: Is detected in poultry, it is normal to cull infected animals and those nearby in an effort to rapidly contain, control and eradicate the disease. This is done together with movement restrictions, improved hygiene and biosecurity, and enhanced surveillance. Humans – Avian flu viruses, both HPAI and LPAI, can infect humans who are in close, unprotected contact with infected poultry. Incidents of cross-species transmission are rare, with symptoms ranging in severity from no symptoms or mild illness, to severe disease that resulted in death. As of February 2024, there have been very few instances of human-to-human transmission, and each outbreak has been limited to

3496-596: Is possible to vaccinate poultry and pigs against specific strains of influenza. Vaccination should be combined with other control measures such as infection monitoring, early detection and biosecurity. The main treatment for mild influenza is supportive; rest, fluids, and over-the-counter medicines to alleviate symptoms while the body's own immune system works to recover from infection. Antiviral drugs are recommended for those with severe symptoms, or for those who are at risk of developing complications such as pneumonia. The symptoms of seasonal flu are similar to those of

3588-648: Is potential for a severe epidemic or pandemic. During early 2017, outbreaks of avian influenza A(H7N9) occurred in poultry in the USA. The strain in these outbreaks was of North American origin and is unrelated to the Asian lineage H7N9 which is associated with human infections in China. In May 2024, an HPAI A/H7N9 was detected on a poultry farm with 160,000 birds in Terang , Australia. There were 14,000 clinically affected birds. It

3680-632: Is potential for low pathogenic avian influenza viruses (LPAI) to evolve into strains which are high pathogenic to poultry (HPAI), and subsequent potential for significant illness and death among poultry during outbreaks. Because of this, international regulations state that any detection of H5 or H7 subtypes (regardless of their pathogenicity) must be notified to the appropriate authority. It is also possible that avian influenza viruses could be transmitted to humans and other animals which have been exposed to infected birds, causing infection with unpredictable but sometimes fatal consequences. When an HPAI infection

3772-548: Is presumed that migratory wild birds were the source of the outbreak. The continuing evolution and antigenic drift of the A/H7N9 virus makes further development difficult as any significant outbreak could involve a completely new strain. A number of human vaccines targeting A/H7N9 have been trialled in relatively small groups of subjects; in the event of any outbreak, a candidate vaccine virus would be distributed to manufacturers Influenza A virus Influenza A virus (IAV)

Influenza A virus subtype H7N9 - Misplaced Pages Continue

3864-477: Is rare. Symptoms of infection vary from mild to severe, including fever, diarrhoea, and cough. As of February, 2024 there have been very few instances of human-to-human transmission, and each outbreak has been limited to a few people. All subtypes of avian Influenza A have potential to cross the species barrier into humans, with H5N1 and H7N9 considered the biggest threats. Prior to 2013, A/H7N9 had previously been isolated only in birds, with outbreaks reported in

3956-488: Is shed by infected birds. The virus can survive for long periods in water and at low temperatures, and can be spread from one farm to another on farm equipment. Domesticated birds (chickens, turkeys, ducks, etc.) may become infected with avian influenza A viruses through direct contact with infected waterfowl or other infected poultry, or through contact with contaminated feces or surfaces. Avian influenza outbreaks in domesticated birds are of concern for several reasons. There

4048-427: Is shed in the saliva, mucus, and feces of infected birds; other infected animals may shed bird flu viruses in respiratory secretions and other body fluids (such as milk). The virus can spread rapidly through poultry flocks and among wild birds. An estimated half billion farmed birds have been slaughtered in efforts to contain the virus. Symptoms of A/H5N1 influenza vary according to both the strain of virus underlying

4140-438: Is spread either through close contact between animals or by the movement of contaminated equipment between farms. Humans who are in close contact with pigs can sometimes become infected. Equine influenza can affect horses, donkeys, and mules; it has a very high rate of transmission among horses, and a relatively short incubation time of one to three days. Clinical signs of equine influenza include fever, nasal discharge, have

4232-441: 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. IAV is an enveloped negative-sense RNA virus , with

4324-443: Is the primary and most effective way to prevent influenza and influenza-associated complications, especially for high-risk groups. Vaccines against the flu are trivalent or quadrivalent, providing protection against the dominant strains of IAV(H1N1) and IAV(H3N2), and one or two influenza B virus strains; the formulation is continually reviewed in order to match the predominant strains in circulation. Poultry and other animals - it

4416-491: The Caspian Sea coastline of Russia's Dagestan republic , worried researchers regarding the possibility that wild mammal-to-mammal spread had begun. A similar mass die-off of 95% of southern elephant seal pups in 2023 also raised concerns of mammal-to-mammal spread, as nursing pups would have had less exposure to birds. Between January and October 2023, at least 24,000 South American sea lions died from H5N1 flu, with

4508-487: The East Asian flyway by wild birds during their annual migration . The genetic characteristics of Asian lineage A/H7N9 virus are of particular concern because of their pandemic potential. The virus is able to infect humans relatively easily, but does not sustain human-to-human transmission. If the virus were to acquire the ability to transmit easily between humans (either through mutation or genetic reassortment) there

4600-572: The Global Influenza Surveillance and Response System (GISRS) monitors the spread of influenza with the aim to inform development of both seasonal and pandemic vaccines. Several millions of specimens are tested by the GISRS network annually through a network of laboratories in 127 countries. As well as human viruses, GISRS monitors avian, swine, and other potentially zoonotic influenza viruses. IAV vaccines need to be reformulated regularly in order to keep up with changes in

4692-629: The Netherlands , Japan , and the United States . Until the 2013 outbreak in China , no human infections with A/H7N9 had been reported. A significant outbreak of Influenza A virus subtype H7N9 (A/H7N9) started in March 2013 when severe influenza affected 18 humans in China; six subsequently died. It was discovered that a low pathogenic strain of A/H7N9 was circulating among chickens, and that all

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4784-420: The World Health Organization has recorded 948 cases of confirmed H5N1 influenza, leading to 464 deaths. The true fatality rate may be lower because some cases with mild symptoms may not have been identified as H5N1. A/H5N1 influenza virus was first identified in farmed birds in southern China in 1996. Between 1996 and 2018, A/H5N1 coexisted in bird populations with other subtypes of the virus, but since then,

4876-584: The World Organization for Animal Health requires all detections of LPAI H5 and H7 subtypes to be reported because of their potential to mutate into highly pathogenic strains. Signs of swine flu in pigs can include fever, depression, coughing (barking), discharge from the nose or eyes, sneezing, breathing difficulties, eye redness or inflammation, and going off feed. Some pigs infected with influenza, however, may show no signs of illness at all. Swine flu subtypes are principally H1N1, H1N2, and H3N2; it

4968-503: The H5N1 subtype which is considered the biggest risk among subtypes. However, because the influenza virus is highly variable, any vaccine needs to be specifically targeted against the particular strain of virus which is causing concern. Existing influenza vaccine technologies can be adapted to a H5N1 strain causing the pandemic; in the event of an outbreak, the candidate vaccine would be rapidly tested for safety as well as efficacy against

5060-402: The affected people had been exposed in poultry markets . Further cases among humans and poultry in mainland China continued to be identified sporadically throughout the year, followed by a peak around the festival season of Chinese New Year (January and February) in early 2014 which was attributed to the seasonal surge in poultry production. Infections among humans and poultry continued during

5152-427: The core of new virions. The predominant natural reservoir of influenza viruses is thought to be wild waterfowl. The subtypes of influenza A virus are estimated to have diverged 2,000 years ago. Influenza viruses A and B are estimated to have diverged from a single ancestor around 4,000 years ago, while the ancestor of influenza viruses A and B and the ancestor of influenza virus C are estimated to have diverged from

5244-409: The envelope and is responsible for uncoating the virion once it has bound to a host cell. The table below presents a concise summary of the influenza genome and the principal functions of the proteins which are encoded. Segments are conventionally numbered from 1 to 8 in descending order of length. PB2 also inhibits JAK1/STAT signaling to inhibit host innate immune response It also degrades

5336-475: The first flu pandemic of the 20th century, known generally as the " Spanish flu ", which caused an estimated 20 to 50 million deaths worldwide. It is now known that this was caused by an immunologically novel H1N1 subtype of influenza A. The next pandemic took place in 1957, the " Asian flu ", which was caused by a H2N2 subtype of the virus in which the genome segments coding for HA and NA appeared to have derived from avian influenza strains by reassortment, while

5428-489: The high lethality and virulence of HPAI A(H5N1), its worldwide presence, its increasingly diverse host reservoir , and its significant ongoing mutations, the H5N1 virus is regarded as the world's largest pandemic threat. Domestic poultry may potentially be protected from specific strains of the virus by vaccination. In the event of a serious outbreak of H5N1 flu among humans, health agencies have prepared "candidate" vaccines that may be used to prevent infection and control

5520-486: The high variability of the virus, subtyping is not sufficient to uniquely identify a strain of influenza A virus. To unambiguously describe a specific isolate of virus, researchers use the Influenza virus nomenclature, which describes, among other things, the subtype, year, and place of collection. Some examples include: The influenza A virus has a negative-sense , single-stranded, segmented RNA genome , enclosed in

5612-413: The highly pathogenic subtype HPAI A(H5N1) has become the dominant strain in bird populations worldwide. Some strains of A/H5N1 which are highly pathogenic to chickens have adapted to cause mild symptoms in ducks and geese, and are able to spread rapidly through bird migration. Mammal species in addition to humans that have been recorded with H5N1 infection include cows, seals, goats, and skunks. Due to

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5704-575: The host cell's mitochondrial antiviral signaling protein At the early stage of infection, the RNP binds to the host cell's importin-α which transports it into the host cell nucleus, where the viral RNA is transcribed and replicated. At a later stage of infection, newly manufactured viral RNA segments assemble with the NP protein and polymerase (PB1, PB2 and PA) to form the core of a progeny virion NA also facilitates

5796-585: The human influenza hemagglutinin prefers to bind to alpha-2,6 sialic acid receptors. This means that when the H5N1 strain infects humans, it will replicate in the lower respiratory tract (where alpha-2,3 sialic acid receptors are more plentiful in humans) and consequently cause viral pneumonia . Between 2003 and November 2024, the World Health Organization has recorded 948 cases of confirmed H5N1 influenza, leading to 464 deaths. The true fatality rate may be lower because some cases with mild symptoms may not have been identified as H5N1. To unambiguously describe

5888-437: The infection and on the species of bird or mammal affected. Classification as either Low Pathogenic Avian Influenza (LPAI) or High Pathogenic Avian Influenza (HPAI) is based on the severity of symptoms in domestic chickens and does not predict the severity of symptoms in other species. Chickens infected with LPAI A/H5N1 virus display mild symptoms or are asymptomatic , whereas HPAI A/H5N1 causes serious breathing difficulties,

5980-496: The infection over large distances; the exact symptoms depend on the species of bird and the strain of virus. Classification of an avian virus strain as HPAI or LPAI does not predict how serious the disease might be if it infects humans or other mammals. Some species of wild aquatic birds act as natural asymptomatic carriers of a large variety of influenza A viruses, which they can spread over large distances in their annual migration. Symptoms of avian influenza vary according to both

6072-736: The leading academic journal Science , the US National Science Advisory Board for Biosecurity (NSABB) recommended against publication of the full details of the study, and the one submitted to Nature by Yoshihiro Kawaoka of the University of Wisconsin describing related work. However, after additional consultations at the World Health Organization and by the NSABB, the NSABB reversed its position and recommended publication of revised versions of

6164-618: The milk. Around 50% of cats that lived on the affected dairy farms and were fed unpasteurised milk from symptomatic cows died within a few days from severe systemic influenza infection, raising significant concerns of cross-species mammal-to-mammal transmission. Novel, contagious strains of H5N1 were created by Ron Fouchier of the Erasmus Medical Center in Rotterdam, the Netherlands, who first presented his work to

6256-531: The movement of infective virus particles through mucus, enabling them to reach host epithelial cells. M1 also assists with the function of the NEP protein. Three viral proteins - PB1, PB2, and PA - associate to form the RNA-dependent RNA polymerase (RdRp) which functions to transcribe and replicate the viral RNA. Viral messenger RNA Transcription - The RdRp complex transcribes viral mRNAs by using

6348-654: The next few years, again with peaks around the new year. In 2016 a virus strain emerged which was highly pathogenic to chickens. In order to contain the HPAI outbreak, the Chinese authorities in 2017 initiated a large scale vaccination campaign against avian influenza in poultry. Since then, the number of outbreaks in poultry, as well as the number of human cases, dropped significantly. In humans, symptoms and mortality for both LPAI and HPAI strains have been similar. Although no human H7N9 infections have been reported since February 2019,

6440-524: The outbreak starting on the Pacific coast of Peru, moving down the coast to Chile and then up the Atlantic coast of Argentina. In April 2024, spread of H5N1 amongst dairy cow herds in nine states of the USA strongly indicated the presence of cow-to-cow transmission possibly occurring while the animals were being milked. Although mortality in bovines infected with H5N1 is rare, viable virus can be shed in

6532-490: The outbreak; however, it could take several months to ramp up mass production. Avian flu viruses, both HPAI and LPAI, can infect humans who are in close, unprotected contact with infected poultry. Incidents of cross-species transmission are rare, with symptoms ranging in severity from no symptoms or mild illness, to severe disease that resulted in death. As of February, 2024 there have been very few instances of human-to-human transmission, and each outbreak has been limited to

6624-558: The public at an influenza conference in Malta in September 2011. Three mutations were introduced into the H5N1 virus genome, and the virus was then passed from the noses of infected ferrets to the noses of uninfected ones, which was repeated 10 times. After these 10 passages the H5N1 virus had acquired the ability of transmission between ferrets via aerosols or respiratory droplets. After Fouchier offered an article describing this work to

6716-414: The relationship between influenza viruses and bacteria, how influenza symptoms progress, and why some influenza viruses are deadlier than others. Past pandemics, and especially the 1918 pandemic, are the subject of much research to understand and prevent flu pandemics. The World Health Organization has published a Research Agenda with five streams: Influenza A virus subtype H5N1 A/H5N1 virus

6808-513: The remainder of the genome was descended from the 1918 virus. The 1968 pandemic (" Hong Kong flu " ) was caused by a H3N2 subtype in which the NA segment was derived from the 1957 virus, while the HA segment had been reassorted from an avian strain of influenza. In the 21st century, a strain of H1N1 flu (since titled H1N1pdm09 ) which was antigenically very different from previous H1N1 strains, leading to

6900-557: The risk of infection. Influenza A/H5N1 was first detected in 1959 after an outbreak of highly pathogenic avian influenza in Scotland, which infected two flocks of chickens. The next detection, and the earliest infection of humans by H5N1, was an epizootic (an epidemic in nonhumans) of H5N1 influenza in Hong Kong's poultry population in 1997. This outbreak was stopped by the killing of the entire domestic poultry population within

6992-522: The same time. Through a combination of mutation and genetic reassortment the virus can evolve to acquire new characteristics, enabling it to evade host immunity and occasionally to jump from one species of host to another. Humans – Several "candidate" (unproved) vaccines are available in case an avian virus acquires the ability to infect and transmit among humans; as of July 2024 these include Aflunov, Celldemic and Seqirus/Audenz. Some governments have prepared strategic stockpiles of vaccines against

7084-520: The same time. Through a combination of mutation and genetic reassortment the virus can evolve to acquire new characteristics, enabling it to evade host immunity and occasionally to jump from one species of host to another. Because of the impact of avian influenza on economically important chicken farms , a classification system was devised in 1981 which divided avian virus strains as either highly pathogenic (and therefore potentially requiring vigorous control measures) or low pathogenic. The test for this

7176-458: The strain of virus underlying the infection and on the species of bird or mammal affected. Classification as either Low Pathogenic Avian Influenza (LPAI) or High Pathogenic Avian Influenza (HPAI) is based on the severity of symptoms in domestic chickens and does not predict the severity of symptoms in humans. Chickens infected with LPAI A/H7N9 virus display mild symptoms or are asymptomatic , whereas HPAI A/H7N9 causes serious breathing difficulties,

7268-492: The strain of virus underlying the infection, and on the species of bird affected. Symptoms of influenza in birds may include swollen head, watery eyes, unresponsiveness, lack of coordination, respiratory distress such as sneezing or gurgling. Because of the impact of avian influenza on economically important chicken farms, avian virus strains are classified as either highly pathogenic (and therefore potentially requiring vigorous control measures) or low pathogenic. The test for this

7360-498: The strain of virus underlying the infection, and on the species of bird affected. Symptoms of influenza in birds may include swollen head, watery eyes, unresponsiveness, lack of coordination, respiratory distress such as sneezing or gurgling. Humans and other mammals can only become infected with avian influenza, including A/H7N9, after prolonged close contact with infected birds or contaminated environments. In mammals including humans, infection with avian influenza (whether LPAI or HPAI)

7452-414: The subtypes and can lead to very significant differences in the virus's ability to infect and cause disease, as well as to the severity of symptoms. Influenza viruses have a relatively high mutation rate that is characteristic of RNA viruses . The segmentation of its genome facilitates genetic recombination by segment reassortment in hosts infected with two different strains of influenza viruses at

7544-427: The territory. Human infection was confirmed in 18 individuals who had been in close contact with poultry, 6 of whom died. Since then, avian A/H5N1 bird flu has become widespread in wild birds worldwide, with numerous outbreaks among both domestic and wild birds. An estimated half a billion farmed birds have been slaughtered in efforts to contain the virus. Influenza viruses have a relatively high mutation rate that

7636-475: The two papers. However, then the Dutch government declared that this type of manuscripts required Fouchier to apply for an export permit in the light of EU directive 428/2009 on dual use goods. After much controversy surrounding the publishing of his research, Fouchier complied (under formal protest) with Dutch government demands to obtain a special permit for submitting his manuscript, and his research appeared in

7728-417: The viral RNA - The replication of the influenza virus, unlike most other RNA viruses , takes place in the nucleus and involves two steps. The RdRp first of all transcribes the negative-sense viral genome into a positive-sense complimentary RNA (cRNA), then the cRNAs are used as templates to transcribe new negative-sense vRNA copies. These are exported from the nucleus and assemble near the cell membrane to form

7820-443: The virus is still circulating in poultry, particularly in laying hens. It has demonstrated antigenic drift to evade vaccines, and remains a potential threat to the poultry industry and public health. As of May 2022, a total of 1568 confirmed A(H7N9) human infections with 616 deaths have been reported, with a case fatality ratio (CFR) of 39%. Genetic characterisation of the "Asian lineage" strain of avian influenza A/H7N9 shows that it

7912-405: The virus over large distances during their migration . The first known case of A/H7N9 influenza infecting humans was reported in March 2013, in China. Cases continued to be recorded in poultry and humans in China over the course of the next 5 years. Between February 2013 and February 2019 there were 1,568 confirmed human cases and 616 deaths associated with the outbreak in China. Initially the virus

8004-622: The virus. There are two methods of classification, one based on surface proteins (originally serotypes ), and the other based on its behavior, mainly the host animal . There are two antigenic proteins on the surface of the viral envelope, hemagglutinin and neuraminidase . Different influenza virus genomes encode different hemagglutinin and neuraminidase proteins. Based on their serotype , there are 18 known types of hemagglutinin and 11 types of neuraminidase. Subtypes of IAV are classified by their combination of H and N proteins. For example, " H5N1 " designates an influenza A subtype that has

8096-949: The winter peak in temperate regions: A zoonosis a disease in a human caused by a pathogen (such as a bacterium , or virus ) that has jumped from a non-human to a human . Avian and pig influenza viruses can, on rare occasions, transmit to humans and cause zoonotic influenza virus infections; these infections are usually confined to people who have been in close contact with infected animals or material such as infected feces and meat, they do not spread to other humans. Symptoms of these infections in humans vary greatly; some are in asymptomatic or mild while others can cause severe disease, leading to severe pneumonia and death. A wide range of Influenza A virus subtypes have been found to cause zoonotic disease. Zoonotic infections can be prevented by good hygiene, by preventing farmed animals from coming into contact with wild animals, and by using appropriate personal protective equipment. As of June 2024, there

8188-434: The zoonotic strain, and then authorised and distributed to vaccine manufacturers. Poultry – it is possible to vaccinate poultry against specific strains of HPAI influenza. Vaccination should be combined with other control measures such as infection monitoring, early detection and biosecurity. In many countries, it is routine to vaccinate poultry against H5N1. In China, the world's biggest poultry producer, there has been

8280-465: Was first discovered in 2009 in little yellow-shouldered bats ( Sturnira lilium ) in Guatemala . In 2012 a second bat influenza A virus IAV(H18N11) was discovered in flat-faced fruit-eating bats ( Artibeus planirostris ) from Peru . Bat influenza viruses have been found to be poorly adapted to non-bat species. Influenza research includes efforts to understand how influenza viruses enter hosts,

8372-481: Was low pathogenic to poultry, however around 2017 a highly pathogenic strain developed which became dominant. The outbreak in China has been partially contained by a program of poultry vaccination which commenced in 2017. Bird-adapted A/H7N9 transmits relatively easily from poultry to humans, although human to human transmission is rare. Its ability to cross the species barrier renders it a potential pandemic threat, especially if it should acquire genetic material from

8464-787: Was not related to A/H7N9 strains previously identified in Europe and North America. This new strain resulted from the recombination of genes between several parent viruses noted in poultry and wild birds in Asia. The H7 gene is most closely related to sequences found in samples from ducks in Zhejiang province in 2011.The N9 gene was closely related to isolated wild ducks in South Korea in 2011. Other genes resembled samples collected in Beijing and Shanghai in 2012. The genes would have been carried along

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