Influenza A virus (IAV) causes influenza in birds and some mammals, and is the only species of the genus Alphainfluenzavirus of the virus family Orthomyxoviridae. Strains of all subtypes of influenza A virus have been isolated from wild birds, although disease is uncommon. Some isolates of influenza A virus cause severe disease both in domestic poultry and, rarely, in humans. Occasionally, viruses are transmitted from wild aquatic birds to domestic poultry, and this may cause an outbreak or give rise to human influenza pandemics.
Avian influenza, known informally as avian flu or bird flu, is a variety of influenza caused by viruses adapted to birds. The type with the greatest risk is highly pathogenic avian influenza (HPAI). Bird flu is similar to swine flu, dog flu, horse flu and human flu as an illness caused by strains of influenza viruses that have adapted to a specific host. Out of the three types of influenza viruses, influenza A virus is a zoonotic infection with a natural reservoir almost entirely in birds. Avian influenza, for most purposes, refers to the influenza A virus.
Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus which can cause illness in humans and many other animal 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) is any strain of the influenza family of viruses that is endemic in pigs. As of 2009, the known SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H2N1, H3N1, H3N2, and H2N3.
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 six major influenza epidemics 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 most recent, the 2009 swine flu pandemic, resulted in under 300,000 deaths and is considered relatively mild. These pandemics occur irregularly.
Singapore has taken a series of measures against avian influenza and the potential threat of a pandemic.
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 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.
Influenza A virus subtype H7N3 (A/H7N3) is a subtype of the species Influenza A virus.
H5N8 is a subtype of the influenza A virus and is highly lethal to wild birds and poultry. H5N8 is typically not associated with humans. However, seven people in Russia were found to be infected in 2021, becoming the first documented human cases.
The social impact of H5N1 is the effect or influence of H5N1 in human society; especially the financial, political, social, and personal responses to both actual and predicted deaths in birds, humans, and other animals. Billions of dollars are being raised and spent to research H5N1 and prepare for a potential avian influenza pandemic. Over ten billion dollars have been lost and over two hundred million birds have been killed to try to contain H5N1. People have reacted by buying less chicken causing poultry sales and prices to fall. Many individuals have stockpiled supplies for a possible flu pandemic.
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.
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 Chinese 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.
H5N6 is a subtype of the species Influenza A virus. Infected birds shed the virus in their saliva, mucous, and feces. The virus was first detected in poultry in 2013, since then spreading among wild bird populations and poultry around the world. Humans can be infected through unprotected contact with infected birds or contaminated surfaces. The virus transmits by getting into a person's eyes, nose, mouth, and through inhalation. Human infections are rare. Since 2014, at least 65 cases have occurred in humans. 29 people have died. A spike in human cases was reported in 2021. There have been no confirmed cases of human-to-human transmission. Some infections have been identified where no direct contact with infected birds or contaminated surfaces has been known to had occurred. Only one infected woman has said that she never came into any contact with poultry.
In the early 2020s, an ongoing outbreak of avian influenza subtype H5N8 has been occurring at poultry farms and among wild bird populations in several countries and continents, leading to the subsequent cullings of millions of birds to prevent a pandemic similar to that of the H5N1 outbreak in 2008. The first case of human transmission was reported by Russian authorities in February 2021, as several poultry farm workers tested positive for the virus.
