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Avian influenza, also known as avian flu or bird flu, is a disease caused by the influenza A virus (IAV) which primarily affects birds but can sometimes affect mammals including humans. Wild aquatic birds are the primary host of Influenza A virus (IAV), which is endemic in many bird populations.
Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus, which causes influenza (flu), predominantly in birds. It is enzootic in many bird populations, and also panzootic. A/H5N1 virus can also infect mammals which have been exposed to infected birds; in these cases symptoms are frequently severe or fatal.
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.
H5N1 genetic structure is the molecular structure of the H5N1 virus's RNA.
Disease surveillance is an epidemiological practice by which the spread of disease is monitored in order to establish patterns of progression. The main role of disease surveillance is to predict, observe, and minimize the harm caused by outbreak, epidemic, and pandemic situations, as well as increase knowledge about which factors contribute to such circumstances. A key part of modern disease surveillance is the practice of disease case reporting.
The global spread of H5N1 in birds is considered a significant pandemic threat.
The global spread of H5N1 in birds is considered a significant pandemic threat.
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.
The Goose Guangdong virus refers to the strain A/Goose/Guangdong/1/96 (Gs/Gd)-like H5N1 HPAI viruses. It is a strain of the Influenzavirus A subtype H5N1 virus that was first detected in a goose in Guangdong in 1996. It is an HPAI virus, meaning that it can kill a very high percentage of chickens in a flock in mere days. It is believed to be the immediate precursor of the current dominant strain of HPAI A(H5N1) that evolved from 1999 to 2002 creating the Z genotype that is spreading globally and is epizootic and panzootic, killing tens of millions of birds and spurring the culling of hundreds of millions of others to stem its spread.
H5N1 influenza virus is a type of influenza A virus which mostly infects birds. H5N1 flu is a concern due to the its global spread that 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.
The global spread of H5N1 in birds is considered a significant pandemic threat.
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.
Cats with avian influenza exhibit symptoms that can result in death. They are one of the few species that can get avian influenza. The viruses cats may get include H5N1 or H7N2, which are subtypes of avian influenza. In order to get the virus, cats need to be in contact with waterfowl, poultry, or uncooked poultry that are infected. Two of the main organs that the virus affects are the lungs and liver.
In 2015, an outbreak of avian influenza subtype H5N2 was identified in a series of chicken and turkey farming operations in the Midwestern United States. By May 30, more than 43 million birds in 15 states had been destroyed as a result of the outbreak, including nearly 30 million in Iowa alone, the nation's largest egg producer. In the Midwestern U.S., the average price of eggs had increased 120% between April 22 and May 30. The effects however were seen nationwide, with prices in California up 71% in the same timeframe.
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 of avian flu, also known as bird flu, was reported by Russian authorities in February 2021, as several poultry farm workers tested positive for the virus.
Since 2020, global outbreaks of avian influenza subtype H5N1 have been occurring, with cases reported from every continent as of May 2024. 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 classified as H5N1 clade 2.3.4.4b, however genetic diversification with other clades such as 2.3.2.1c has seen the virus evolve in ability to cause significant outbreaks in a broader range of species including mammals.
References
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- 1 2 Nuki, Paul (2 February 2023). "How worried should we be about avian flu?". The Telegraph. Archived from the original on 2 February 2023. Retrieved 5 February 2023.
- 1 2 3 Pelley, Lauren (2 February 2023). "Bird flu keeps spreading beyond birds. Scientists worry it signals a growing threat to humans, too". CBC News. Archived from the original on 2 February 2023. Retrieved 5 February 2023.
- ↑ "Highly Pathogenic Avian Influenza (HPAI) H5N1 Detections in Alpacas". USDA. APHIS. Retrieved 29 May 2024.
- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 "2022-2023 Detections of Highly Pathogenic Avian Influenza in Mammals". Avian Influenza. USDA APHIS. Archived from the original on 30 January 2023. Retrieved 5 February 2023.
- ↑ Schnirring, Lisa (20 July 2023). "H5N1 avian flu strikes more Finnish fur farms, second fox species". University of Minnesota. CIDRAP. Retrieved 21 March 2024.
- ↑ Merrick, Jane (1 February 2023). "Mass death of seals raises fears bird flu is jumping between mammals, threatening new pandemic". The i newspaper. Archived from the original on 3 February 2023. Retrieved 15 February 2023.
- ↑ Schnirring, Lisa (25 March 2024). "Sick cows in 2 states test positive for avian flu". University of Minnesota. CIDRAP. Retrieved 26 March 2024.
- 1 2 Hinds, Tom (22 January 2024). "Catastrophic Mortality of Elephant Seals in Argentina Identified as Outbreak of Avian Influenza". UC Davis. Veterinary Medecine. Retrieved 21 March 2024.
- ↑ Balla, Reemul (2 February 2023). "Bird flu found in nine otters and foxes since 2021". Sky News. Archived from the original on 3 February 2023. Retrieved 6 February 2023.
- ↑ Schnirring, Lisa (20 March 2024). "Avian flu detected for first time in US livestock". University of Minnesota. CIDRAP. Retrieved 21 March 2024.
- ↑ "Past Reported Global Human Cases with Highly Pathogenic Avian Influenza A(H5N1) (HPAI H5N1) by Country, 1997-2024". cdc.gov. Centres for Disease Control and Prevention. Retrieved 21 March 2024.
- ↑ Weston, Phoebe (2 January 2024). "Polar bear dies from bird flu as H5N1 spreads across globe". The Guardian. Archived from the original on 4 January 2024. Retrieved 4 January 2024.
- ↑ Rijks, Jolianne; Hesselink, Hanna; Lollinga, Pim; Wesselman, Renee; Prins, Pier; Weesendorp, Eefke; Engelsma, Marc; Heutink, Rene; Harders, Frank; Kik, Marja; Rozendaal, Harry; van den Kerkhof, Hans; Beerens, Nancy (November 2021). "Highly Pathogenic Avian Influenza A(H5N1) Virus in Wild Red Foxes, the Netherlands, 2021". Emerging Infectious Diseases. 27 (11): 2960–2962. doi:10.3201/eid2711.211281. PMC 8544991 . PMID 34670656.
- ↑ Prater, Erin (8 February 2023). "The spillover of bird flu to mammals must be 'monitored closely,' WHO officials warn: 'We need to be ready to face outbreaks in humans'". Fortune. Archived from the original on 9 February 2023. Retrieved 9 February 2023.