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 influenza (flu), predominantly in birds. 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.
Chick culling or unwanted chick killing is the process of separating and killing unwanted chicks for which the intensive animal farming industry has no use. It occurs in all industrialised egg production, whether free range, organic, or battery cage. However, some certified pasture-raised egg farms are taking steps to eliminate the practice entirely. Worldwide, around 7 billion male chicks are culled each year in the egg industry. Because male chickens do not lay eggs and only those in breeding programmes are required to fertilise eggs, they are considered redundant to the egg-laying industry and are usually killed shortly after being sexed, which occurs just days after they are conceived or after they hatch. Some methods of culling that do not involve anaesthetics include: cervical dislocation, asphyxiation by carbon dioxide, and maceration using a high-speed grinder. Maceration is the primary method in the United States. Maceration is often a preferred method over carbon dioxide asphyxiation in western countries as it is often considered as "more humane" due to the deaths occurring immediately or within a second.
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 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.
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 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.
Poultry farming is the form of animal husbandry which raises domesticated birds such as chickens, ducks, turkeys and geese to produce meat or eggs for food. Poultry – mostly chickens – are farmed in great numbers. More than 60 billion chickens are killed for consumption annually. Chickens raised for eggs are known as layers, while chickens raised for meat are called broilers.
The 2008 bird flu outbreak in West Bengal was an occurrence of avian influenza in West Bengal, India which began in January 2008. The infection was caused by the H5N1 subtype of the Influenza A virus and impacted at least thirteen districts, including Birbhum, Nadia, Murshidabad, Burdwan, Hooghly, Cooch Behar, Malda, Bankura, Purulia, Howrah, West Midnapore, South 24 Parganas and South Dinajpur. A range of precautions were instituted including a large cull of chickens, eggs, and poultry birds, the imposition of segregation zones, and a disinfection programme for the plant. The government put a blanket ban on the movement of poultry birds from West Bengal 5 February 2008, but repealed it a week later.
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.
Rembrandt Enterprises (REI) is an American company headquartered in Spirit Lake, Iowa. The company was founded in 2000 and is named after its egg operation in Rembrandt, Iowa. The company runs one of the world's largest egg producing and processing facilities. The company has faced criticism for their treatment of hens generally along with the usage of ventilation shutdown and treatment of workers following the appearance of avian influenza in March 2022.
H5N6 is a subtype of the species Influenza A virus. Infected birds shed the virus in their saliva, mucus, 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 94 cases have occurred in humans. 37 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 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.
From April to September 2017 in the Philippines, an outbreak of H5N6 avian influenza or bird flu affected poultry in at least three towns in Central Luzon; San Luis in Pampanga and Jaen and San Isidro in Nueva Ecija.
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.
Ventilation shutdown (VSD) is a means to kill livestock by suffocation and heat stroke in which airways to the building in which the livestock are kept are cut off. It is used for mass killing — usually to prevent the spread of diseases such as avian influenza. Animal rights organizations have called the practice unethical. The addition of carbon dioxide or additional heat to the enclosure is known as ventilation shutdown plus (VSD+).
Since 2020, outbreaks of avian influenza subtype H5N1 have been occurring, with cases reported from every continent except Australia as of November 2024. 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 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.
