explained-what-is-h5n1-avian-influenza-its-symptoms-and-how-fatal-can-it-be

Context: Recently, the first recorded death due to the bird flu (H5N1 avian influenza) was in Delhi, India in 2021.

Background:

  • Recently China has confirmed the first instance of human infection from H10N3, a rare strain of a virus that normally infects poultry.
  • As always the National Health Commission of Beijing provides no details on how the virus was contracted.

About H10N3:

  • According to the Beijing-based National Health Commission, the strain has low pathogenesis (the ability to cause disease) among birds.
    • It implies that the virus did not spread easily among poultry and was likely to be restricted to limited populations.
  • According to WHO the avian influenza viruses circulate in poultry and occasionally it transfers into humans as well.
  • So far, the H10N3 appears mild and not very transmissible, and hence, its categorisation status remains unclear.

About Avian influenza:

  • H5N1 is the most common virus causing bird flu, or avian influenza.
  • Avian influenza is largely restricted to birds, and often fatal to them
    • It can cross over to other animals, as well as humans.
  • According to the WHO, the H5N1 was first discovered in humans in 1997 and has killed almost 60% of those infected.
  • There are several subtypes of the avian influenza virus.
    • Avian Influenza type A viruses are classified based on two proteins on their surfaces – 
      • Hemagglutinin(HA) and 
      • Neuraminidase(NA)
    • There are about 18 HA subtypes and 11 NA subtypes. 
      • Several combinations of these two proteins are possible e.g., H5N1, H7N2, H9N6, H17N10, etc.
    • Since 2003, these avian and other influenza viruses have spread from Asia to Europe and Africa.
    • In 2013, human infections with the influenza A (H7N9) virus were reported in China.
      • An outbreak of the H7N9 strain killed around 300 people in 2016 and 2017.
    • According to the US Centre for Disease Control and Prevention;
      • All known subtypes of influenza A viruses can infect birds, except subtypes H17N10 and H18N11, which have only been found in bats.
      • Only two influenza A virus subtypes (i.e., H1N1, and H3N2) are currently in general circulation among people.
      • Some subtypes are found in other infected animal species.
        • For example, H7N7 and H3N8 virus infections can cause illness in horses.
        • H3N8 virus infection causes illness in horses and dogs.
  • The virus can infect domestic poultry including chickens, ducks, turkeys and there have been reports of H5N1 infection among pigs, cats, and even tigers in Thailand zoos.

Typical symptoms of avian influenza infection:

  • According to the WHO, avian, swine and other zoonotic influenza virus infections in humans may cause disease with symptoms like:
    • Mild upper respiratory tract infection (fever and cough), 
    • Early sputum production and rapid progression to severe pneumonia,
    • Sepsis with shock, 
    • Acute respiratory distress syndrome, and 
    • Even death.
  • Conjunctivitis, gastrointestinal symptoms, encephalitis and encephalopathy have also been reported in varying degrees depending on the subtype.

Risk group:

  • Children and adults below 40 were seen to be the most affected and mortality was high in 10-19 years olds.

Human to Human Transmission:

  • The human-to-human transmission of the H5N1 virus was very rare.
  • The transmission of the virus from birds to humans is rare and sustained human-to-human transmission of the H5N1 virus has not yet been established.

Why are bird flu viruses a cause of concern?

  • Speculation about the origin of the SARS-CoV-2 has heightened worries about the animal- and bird-borne viruses.
  • The emergence of new strains, particularly among domesticated animals and birds, is a story of evolution and inevitability, and sporadic reports of new viruses infecting humans abound.
  • An outbreak of the H5N8 virus in birds led to hundreds of thousands of poultry being culled in various European countries.
  • In February, Russia reported that seven poultry workers in a plant were infected by the H5N8 strain.
    • All of them recovered.
  • India, too, faced an outbreak of the virus in flocks of poultry in January and undertook culling.

Related Facts:

About the H5N1 strain in India:

  • It is severe and deadly. 
  • If the virus mutates and becomes easily transmissible from person to person, it can potentially cause a pandemic. 
  • Bird flu in India: 
    • The department of animal husbandry has reported 25 episodes of H5N1 bird flu in poultry in 15 states from 2006 till 2015. 
    • According to the Union health ministry, no case of bird flu in humans has been detected so far in India.

Source:https://indianexpress.com/article/explained/explained-what-is-h5n1-avian-influenza-its-symptoms-and-how-fatal-can-it-be-7415702/