Influenza A virus (IAV) is a pathogen that causes the flu in birds and some mammals, including humans. It is an RNA virus whose subtypes have been isolated from wild birds. Occasionally, it is transmitted from wild to domestic birds, and this may cause severe disease, outbreaks, or human influenza pandemics.
Avian influenza, also known as avian flu, is a bird flu caused by the influenza A virus, which can infect people. It is similar to other types of animal flu in that it is caused by a virus strain that has adapted to a specific host. The type with the greatest risk is highly pathogenic avian influenza (HPAI).
Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus which can cause illness in humans and many other species. A bird-adapted strain of H5N1, called HPAI A(H5N1) for highly pathogenic avian influenza virus of type A of subtype H5N1, is the highly pathogenic causative agent of H5N1 flu, commonly known as avian influenza. It is enzootic in many bird populations, especially in Southeast Asia. One strain of HPAI A(H5N1) is spreading globally after first appearing in Asia. It is epizootic and panzootic, killing tens of millions of birds and spurring the culling of hundreds of millions of others to stem its spread. Many references to "bird flu" and H5N1 in the popular media refer to this strain.
Swine influenza is an infection caused by any of several types of swine influenza viruses. Swine influenza virus (SIV) or swine-origin influenza virus (S-OIV) refers to any strain of the influenza family of viruses that is endemic in pigs. As of 2009, identified SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H2N1, H3N1, H3N2, and H2N3.
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 recent, 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 recent 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.
Influenza A virus subtype H7N7 (A/H7N7) is a subtype of Influenza A virus, a genus of Orthomyxovirus, the viruses responsible for influenza. Highly pathogenic strains (HPAI) and low pathogenic strains (LPAI) exist. H7N7 can infect humans, birds, pigs, seals, and horses in the wild; and has infected mice in laboratory studies. This unusual zoonotic potential represents a pandemic threat.
Influenza A virus subtype H9N2 (A/H9N2) is a subtype of the species Influenza A virus . Since 1998 a total of 86 cases of human infection with H9N2 viruses have been reported.
H6N2 is an avian influenza virus with two forms: one has a low and the other a high pathogenicity. It can cause a serious problem for poultry, and also infects ducks as well. H6N2 subtype is considered to be a non-pathogenic chicken virus, the host still unknown, but could strain from feral animals, and/or aquatic bird reservoirs. H6N2 along with H6N6 are viruses that are found to replicate in mice without preadaptation, and some have acquired the ability to bind to human-like receptors. Genetic markers for H6N2 include 22-amino acid stalk deletion in neuraminidase (NA) protein gene, increased N-glycosylation, and a D144 mutation of the Haemagglutinin (HA) protein gene. Transmission of avian influenza viruses from wild aquatic birds to domestic birds usually cause subclinical infections, and occasionally, respiratory disease and drops in egg production. Some histological features presented in chicken infected with H6N2 are fibrinous yolk peritonitis, salpingitis, oophoritis, nephritis, along with swollen kidneys as well.
H5N1 genetic structure is the molecular structure of the H5N1 virus's RNA.
Spanish flu research concerns studies regarding the causes and characteristics of the Spanish flu, a variety of influenza that in 1918 was responsible for the worst influenza pandemic in modern history. Many theories about the origins and progress of the Spanish flu persisted in the literature, but it was not until 2005, when various samples of lung tissue were recovered from American World War I soldiers and from an Inupiat woman buried in permafrost in a mass grave in Brevig Mission, Alaska, that significant genetic research was made possible.
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.
Human mortality from H5N1 or the human fatality ratio from H5N1 or the case-fatality rate of H5N1 is the ratio of the number of confirmed human deaths resulting from confirmed cases of transmission and infection of H5N1 to the number of those confirmed cases. For example, if there are 100 confirmed cases of humans infected with H5N1 and 10 die, then there is a 10% human fatality ratio. H5N1 flu is a concern due to the global spread of H5N1 that constitutes a pandemic threat. The majority of H5N1 flu cases have been reported in southeast and east Asia. The case-fatality rate is central to pandemic planning. Estimates of case-fatality (CF) rates for past influenza pandemics have ranged from to 2-3% for the 1918 pandemic to about 0.6% for the 1957 pandemic to 0.2% for the 1968 pandemic. As of 2008, the official World Health Organization estimate for the case-fatality rate for the outbreak of H5N1 avian influenza was approximately 60%. Public health officials in Ontario, Canada argue that the true case-fatality rate could be lower, pointing to studies suggesting it could be 14-33%, and warned that it was unlikely to be as low as the 0.1–0.4% rate that was built into many pandemic plans.
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 from one to four days after exposure to the virus and last for about 2–8 days. Diarrhea and vomiting can occur, particularly in children. Influenza may progress to pneumonia, which can be caused by the virus or by a subsequent bacterial infection. Other complications of infection include acute respiratory distress syndrome, meningitis, encephalitis, and worsening of pre-existing health problems such as asthma and cardiovascular disease.
Influenza A virus subtype H7N9 (A/H7N9) is a bird flu strain of the species Influenza virus A. Avian influenza A H7 viruses normally circulate amongst avian populations with some variants known to occasionally infect humans. An H7N9 virus was first reported to have infected humans in March 2013, in China. Cases continued to be reported throughout April and then dropped to only a few cases during the summer months. At the closing of the year, 144 cases had been reported of which 46 had died. It is known that influenza tends to strike during the winter months, and the second wave, which began in October, was fanned by a surge in poultry production timed for Lunar New Year feasts that began at the end of January. January 2014 brought a spike in reports of illness with 96 confirmed reports of disease and 19 deaths. As of April 11, 2014, the outbreak's overall total was 419, including 7 in Hong Kong, and the unofficial number of deaths was 127.
Influenza A virus subtype H6N1 (A/H6N1), is a subtype of the influenza A virus. It has only infected one person, a woman in Taiwan, who recovered. Known to infect Eurasian teal, it is closely related to subtype H5N1.
Chen Hualan is a Chinese veterinary virologist best known for researching animal epidemic diseases. She is a member of the World Organisation for Animal Health (OIE) and a member of the Food and Agriculture Organization Corporate Statistical Database (FAOSTAT). She is now a researcher and PhD Supervisor at Harbin Veterinary Research Institute of Chinese Academy of Agricultural Sciences.
Influenza A virus subtype H10N3 is a subtype of viruses that causes influenza (flu). It is mostly present in wild avian species. The first human case was reported in 2021.
