Mutation of the Avian Flu Virus

The genetic sequence of an avian flu virus strain gradually changes, or mutates, over time. The changing of the virus genome happens in two ways: antigenic drift and antigenic shift.

Antigenic drift

Antigenic drift refers to the random, spontaneous mutations in viruses’ RNA that happen over time. These mutations are small, usually the alteration of one nucleotide at a time. Viruses will gradually accumulate more and more mutations in their RNA, eventually causing them to become new strains.

 

Antigenic shift

Antigenic shift is a very large and sudden mutation (changing of many nucleotides/many genes), that happens all at once. Antigenic shift happens when two different types of virus infect the same cell. The viruses’ RNA get mixed up, forming new viruses that have major changes in their genome.

 

Effects of Mutation

Mutation in viruses can cause changes in characteristics, such as infectious ability, pathogenicity, and surface protein shape. The things that are changed, and how much they are changed, depend on how and where the RNA was mutated. For example, mutation in the hemagglutinin gene could cause the hemagglutinin surface proteins to slightly alter its shape, or completely change the surface protein type (ex. H3 to H5), depending on how the RNA was mutated.

Mutation allows viruses to get past the body’s immunity to the virus. Suppose a virus strain infects someone, and the person’s immune system fights the virus off and develops immunity to the specific strain of virus. The virus could mutate (through antigenic shift or drift), and infect the same person again. Because the virus mutated, the person’s immune system would not recognize the new virus strain, and therefore would not have immunity to it.