what year was the bird flu

Bird flu is an infection caused by avian influenza viruses, which are of different types A, B and C. Type A avian influenza viruses are the most frequently associated with avian influenza epidemics and pandemics. There are 16 hemagglutinin (H1 to H16) and 9 neuraminidase types (N1 to N9) identified till date. A peculiar characteristic of influenza A viruses is their propensity for genetic change by two main processes: antigenic drift (small, gradual changes) and antigenic shift (abrupt, major change producing a novel influenza A virus subtype).

There are various modes of transmission of human influenza including inhalation, direct or indirect (fomite) contact etc., can have manifestations ranging from mild to severe or fatal disease, depend on the viral subtype causing the disease. Avian influenza A (H5N1) results in high death rate amongst infants and young children.

The first outbreak of human infection by avian influenza viruses (H5N1) was observed in 1997 in Hong Kong. Since then a large number of outbreaks have been reported in different parts of the world. In fact, the spread of avian influenza H5N1 in various species including humans has lead to a current pandemic threat.

Human avian influenza infections in persons at high risk of exposure can be prevented by adopting a series of protective measures, anti-viral vaccination and health monitoring. Drugs currently available for the treatment or prophylaxis of influenza infections include the adamantanes (amantadine and rimantadine) and the newer class of neuraminidase inhibitors (zanamivir, oseltamivir and peramivir). However, vaccines are considered the first line of defense for reducing the excess morbidity and mortality that invariably accompany pandemics and a number of clinical trials are under way to test them.

Avian influenza (bird flu), an infection caused by avian influenza viruses has emerged as the primary public health concern of the 21st century. There are three types of influenza viruses, designated A, B and C. Variants of this species are sometimes named according to the species the strain is endemic in or adapted to for example, human flu, swine flu, horse Flu, dog flu etc.

Human infections with avian influenza

The first worrying indication that avian influenza viruses (H5N1) could directly infect humans from avian species happened in Hong Kong in 1997; there were 18 confirmed cases and six fatalities as a result. Contrary to prior theories that the avian influenza virus cannot infect humans because of differences in receptors, the year 2003 saw a shift in virus strains that led to the emergence of the “novel” Z strain and its infection of humans. Bird flu outbreaks occurred in 13 new countries in February 2006, including many regions of India. (6) Of the numerous highly pathogenic avian viruses that have surfaced in recent years, H5N1 is the most virulent subtype. (3).

Nations with Confirmed Cases H5N1 Avian Influenza (May 2007)(10)

Outbreaks of human avian influenza (3,8)

H5N1; Hong kong, H7N7; Netherlands, H9N2; Hong kong

2004/05: Egypt H5N1 in 13 new countries, including India; H7N3 in Canada; H10N7 in Egypt; and H5N1 in China, Egypt, Indonesia, and Nigeria

Total A/H5N1 Avian Influenza A/Confirmed Human Cases Reported to WHO(11) (as of April 11, 2007)

Country 2003 2004 2005 2006 2007 Total
cases deaths cases deaths cases deaths cases deaths cases deaths cases deaths
Azerbaijan 0 0 0 0 0 0 8 5 0 0 8 5
Cambodia 0 0 0 0 4 4 2 2 1 1 7 7
China 1 1 0 0 8 5 13 8 2 1 24 15
Djibouti 0 0 0 0 0 0 1 0 0 0 1 0
Egypt 0 0 0 0 0 0 18 10 16 4 34 14
Indonesia 0 0 0 0 20 13 55 45 6 5 81 63
Iraq 0 0 0 0 0 0 3 2 0 0 3 2
Lao People’s Democratic Republic 0 0 0 0 0 0 0 0 2 2 2 2
Nigeria 0 0 0 0 0 0 0 0 1 1 1 1
Thailand 0 0 17 12 5 2 3 3 0 0 25 17
Turkey 0 0 0 0 0 0 12 4 0 0 12 4
Viet Nam 3 3 29 20 61 19 0 0 0 0 93 42
Total 4 4 46 32 98 43 115 79 28 14 291 172

Clinical features and prognosis of avian influenza infection in humans

Healthy-looking waterfowl, especially ducks, excrete the avian influenza A virus, which subsequently infects chickens and other poultry that they come into contact with. Asia provides an ideal environment for both species-jumping and transmission because of the high population density of humans, poultry, ducks, and pigs there. (3) Human influenza is spread through self-inoculation onto the upper respiratory tract or conjunctival mucosa, inhalation of infectious droplets and droplet nuclei, direct contact, and possibly indirect (fomite) contact. (4).

Depending on the virus subtype causing the illness, avian influenza infections can present with a variety of clinical symptoms. (1) Avian influenza A (H5N1) has a highly variable incubation period; cases have been reported to occur 2-4 days after exposure and up to 8-17 days later. Most patients experience high fever as their initial symptom ( Early in the course of some patients’ illnesses, reports of diarrhea, vomiting, abdominal pain, pleuritic pain, and bleeding from the gums and nose have also been made. A common side effect of infections caused by avian influenza A (H7) viruses is conjunctivitis.

Avian influenza can cause a number of complications, such as pancytopenia, Reye’s syndrome, sepsis syndrome without proven bacteremia, ventilator-associated pneumonia, pulmonary hemorrhage, multi-organ failure with signs of renal dysfunction and cardiac compromise, and pneumothorax. (4).

Avian influenza A (H5N1) causes a high death rate among infants and young children, with a case fatality rate of 20%89% among those under the age of five years old. The majority of patients pass away from progressive respiratory failure, and deaths happen nine or ten days after the illness first manifests. (5).

A nasopharyngeal aspirate taken within three days of the onset of symptoms is the ideal specimen, however a nasopharyngeal swab can also be taken. There are several techniques for detection, including real-time polymerase chain reaction (RT-PCR), virus culture, and rapid antigen assays. (5).

Due to the avian influenza H5N1 virus’s proven ability to infect humans across species boundaries and its current global spread among domestic poultry flocks and wild birds, there is significant concern that a pandemic may break out. Three requirements have been identified for the emergence of a pandemic: the virus must be a new subtype to which the population has little to no immunity; it must be able to replicate in humans and cause serious illness; and it must be able to spread from person to person efficiently. (6) H5N1 has been identified as a potential pandemic candidate for nearly ten years, in contrast to most pandemics, which appear at random.

The World Health Organization’s experts classify the current state of the pandemic alert as stage 3. (3).

Genomic structure of virus

The influenza virus is a member of the single-stranded, minus-sense RNA orthomyxoviridae family of viruses, which also includes viruses with segmented genomes. The influenza A virus’s genome consists of eight RNA segments that encode eleven viral proteins. These comprise the matrix proteins (M1, M2), nonstructural proteins (NS1, NS2), hemagglutinin, neuraminidase, nucleocapsid protein, and polymerase proteins (PB1, PB2, PA, PB1-F2).

The primary antigenic determinants of influenza A viruses are hemagglutinin and neuraminidase, which form the foundation for the subtype classification of these viruses. Nine neuraminidase types (N1 to N9) and sixteen hemagglutinin types (H1 to H16) exist. The different influenza A virus subtypes’ host specificity is partially explained by hemagglutinin, which binds to sialic acid receptors on the cell surface to facilitate the virus’s attachment to and entry into host cells. However, the specificity of how A/H5N1 viruses bind to receptors can be altered by altering just one amino acid in the H5 protein. Thus, the barrier to interspecies infection can be overcome easily. Additionally, by neutralizing antibodies, hemagglutinin forms the primary viral target of protective humoral immunity.

Neuraminidase, which is the target of neuraminidase inhibitors, cleaves the glycosidic linkages to sialic acid on the surface of the viral particles and host cells, facilitating the spread of the virions within the host. M2 is an ion channel that is essential for the pH-dependent release of matrix proteins from the nucleocapsid during viral uncoating and for the pH variations that occur throughout the trans-Golgi network when hemagglutinin molecules mature. M2 is the target of the adamantanes (amantadine and rimantadine). Adantanes are always resistant to a mutation in the M2 molecule that changes serine to asparagine at residue 31.

PB1-F2 causes cellular apoptosis by acting on the host mitochondria. The determination of host specificity and virulence seems to be influenced by the hemagglutinin and PB2 proteins. (1).

Types of bird flu viruses infecting birds and humans (2)

Influenza A H5: Nine potential subtypes of H5 are known. Human H5 infections have been reported to occasionally cause serious illness or even death. One example of such an infection is the HPAI H5N1 virus, which is presently circulating in Asia and Europe.

Influenza A H7: Nine potential subtypes of H7 are known. Although it is uncommon, H7 infection in humans can happen to those who have close contact with infected birds. Symptoms may include conjunctivitis and/or upper respiratory symptoms. H7 viruses have been associated with both LPAI (e. g. , H7N2, H7N7) and HPAI (e. g. , H7N3, and H7N7), and have sickened people from mild to fatal.

Influenza A H9: There are nine identified subtypes of H9, although human infections with influenza A H9 are uncommon. However, only a low pathogenic form of this subtype has been reported.

Influenza Type B These are usually found only in humans. In contrast to influenza A viruses, these viruses do not have subtype classification. Although influenza B viruses are generally linked to less severe epidemics than influenza A viruses, they can still cause morbidity and mortality in humans. Type B influenza viruses have not resulted in pandemics, despite their ability to cause epidemics in humans.

Influenza Type C viruses do not spread epidemics or pandemics, but they do cause mild illness in humans. These viruses are not classified according to subtype.

Low vs Highly pathogenic avian influenza viruses (2)

Influenza virus A is divided into low pathogenic (LPAIA) and high pathogenic (HPAIA) viruses based on distinct molecular genetic and pathogenesis criteria that necessitate particular testing. However, low pathogenic can evolve into high pathogenic viruses. The HPAIA viruses H5, H7, H5N1, H7N7, and H7N3 can cause human infections that range in severity from mild (H7N3, H7N7) to severe and lethal (H7N7, H5N1). LPAIA viruses causing infection in humans include H7N7, H9N2, H7N2.

A constantly mutating virus: 2 consequences

Influenza A viruses are known for their propensity to undergo genetic alteration through two primary processes: antigenic drift and antigenic shift. The term “antigenic drift” describes minute, progressive alterations brought about by point mutations in the two genes—hemagglutinin and neuraminidase—that carry the genetic material responsible for producing the two primary surface proteins. These point mutations cause small alterations to these surface proteins and happen randomly. An antigenic shift is a sudden, significant alteration that results in the production of a novel influenza A virus subtype in humans that was not previously circulating in the population. It can spread either directly from animal (poultry) to human or indirectly through the process of genetic reassortment, which involves combining the genes of the human influenza A virus with those of the animal influenza A virus to produce a new subtype of the human influenza A virus. (2).

An overview of notable avian HPAI and LPAI outbreaks, human infections, and events from 2020 to 2022 can be found in the timeline below.


When was the bird flu outbreak?

The first infected commercial flock was identified on January 23, 2015, in California. From January to March, the disease spread slowly to multiple states, including Minnesota, Missouri, Arkansas, and Kansas.

What years were the worst bird flu?

United States 2014–15 outbreak From 2014 through 2015, United States poultry and egg producers experienced the largest outbreak of H5N2 in recorded history with approximately 51 million birds depopulated to control the spread of the disease.

Was there a bird flu outbreak in 2014?

H5 Outbreaks, 2014-2015 Beginning in January 2015 to June 2015, HPAI (H5) virus outbreaks were reported in commercial poultry flocks in 21 U.S. states and Canada. HPAI viruses also were detected in captive and wild birds in 2014 and 2015 in the U.S. and Canada. No transmission of HPAI (H5) virus to humans was reported.

Was there a bird flu pandemic in 1997?

In 1997, a high-pathogenicity H5N1 avian influenza virus caused serious disease in both man and poultry in Hong Kong, China. Eighteen human cases of disease were recorded, six of which were fatal. This unique virus was eliminated through total depopulation of all poultry markets and chicken farms in December 1997.