Antigenic shift

Diagram illustrating antigenic shift.

Antigenic shift is a process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the original strains. This process is known to occur in influenza A virus and is a major cause of pandemics.

Mechanism

Antigenic shift occurs when an influenza virus from a non-human animal, such as a bird or pig, infects a human and exchanges genetic material with a human influenza virus. This can result in a new influenza A subtype that is capable of infecting humans and spreading rapidly, as the human population has little to no pre-existing immunity to the new subtype.

The process of antigenic shift is distinct from antigenic drift, which involves the gradual accumulation of mutations within the genes that code for the virus's surface proteins, leading to small changes in the antigens over time. Antigenic shift, on the other hand, involves a sudden and major change in the virus's antigens.

Impact on Public Health

Antigenic shift can lead to the emergence of a novel influenza virus against which the human population has little immunity, potentially resulting in widespread illness and increased mortality. This phenomenon is responsible for the occurrence of influenza pandemics, such as the Spanish flu of 1918, the Asian flu of 1957, and the Hong Kong flu of 1968.

Examples

The 2009 H1N1 influenza pandemic, also known as "swine flu," was a result of antigenic shift. The virus contained a unique combination of gene segments from human, avian, and swine influenza viruses, which allowed it to spread rapidly among humans.

Related Pages

• Influenza A virus
• Pandemic
• Antigenic drift
• Spanish flu
• Asian flu
• Hong Kong flu