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Why bird flu virus has so many strains and what it means for humans?

Topics Covered: Issues related to Health.

Why bird flu virus has so many strains and what it means for humans?


Two different subtypes of the bird flu virus or avian influenza have been detected in Himachal Pradesh.

How many different subtypes or strains of the flu A virus are out there?

At least 131 different subtypes of influenza A virus have been detected in nature.

  • The influenza A virus has two proteins on its surface hemagglutinin (H) and neuraminidase (N) both of which have 18 and 11 different subtypes respectively, leading to different combinations such as H3N2 and H7N9.
  • There are some strains which only infect birds, while others can infect birds as well as mammals such as pigs, dogs, horses and also humans.

How many of these strains can infect humans?

Mostly, humans have only experienced infections by three different H types (H1, H2 and H3), and two different N types (N1 and N2).

  • Presently, two subtypes, H1N1 and H3N2, circulate among human beings, causing the seasonal flu epidemics. Since these strains are well adapted to humans, they are referred to as human flu rather than bird flu.
  • Whenever a new flu A virus establishes itself in humans, it can cause a pandemic, and four such pandemics have occurred since 1918, including the Spanish flu (H1N1), the 1957-58 Asian flu (H2N2), the 1968 Hong Kong flu (H3N2) and the 2009 swine flu (caused by a newer version of the H1N1).

Why does the flu A virus have so many strains?

Influenza A virus mutates constantly and this is because:

  1. Firstly, It is an RNA virus with a segmented genome, i.e. it has eight separate strands, which makes its copying prone to errors or mutations. This ‘antigenic drift’ results in slight but continuous mutations in the surface proteins, which is the reason why flu vaccines have to be updated regularly.
  2. Secondly, when a cell happens to be infected with two different flu A viruses, their genes can easily get mixed up. This mixing, known as reassortment, is a viral version of sex.



Prelims Link:

  1. When a country is declared free from Avian Influenza, who declares it?
  2. H5N1 vs H5N6 vs H9N2 vs H5N8.

Mains Link:

Write a note on Bird Flu. Discuss how it can be prevented.

Sources: Indian Express.