Question

Describe the difference between antigenic shift and antigenic drift in viral pathogens.

Answer 1

Viral pathogens are constantly mutating hence it becomes difficult to treat. This constant mutations among the pathogenic viruses is due to two mechanisms in the viral genome namely antigenic shift and antigenic drift.

Antigenic shift is the sudden change in the antigenicity of viruses due to reassortment of genes which results in the formation of a new viral subtype. It results in major antigenic change in the virus and it occurs less frequently but as it causes major change in the antigenicity, the new viral subtype becomes difficult to treat. The new viral subtype can infect hosts from different species. It spreads very rapidly and causes global pandemics. In influenza virus it occurs in only type A influenza virus.

Antigenic drift is the gradual accumulation of genetic mutations in the viral genome which changes the antigenicity of the virus and results in the evolution of new virus strain. This new virus strain can infect individuals of the same species. Due to change in the antigenicity of the virus, the new viral surface proteins are difficult for the host's antibodies to recognise which makes the host susceptible to viral infection by this new viral strain. It causes minor changes in the antigenicity of the virus hence it is comparatively easier to treat than antigenic shift. It results in the major epidemics and in influenza virus it can occur in type A, type B and type C influenza virus.