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Antigenic drift
 
 
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Antigenic drift is the process of random accumulation of mutations in viral genes recognized by the immune system
Immune system

An immune system is a collection of biological processes within an organism that protects against disease by identifying and killing pathogens and tumour cells....
. Such accumulation may significantly change the antigen
Antigen

An antigen is a substance that prompts the generation of antibodies and can cause an immune response. The word originated from the notion that they can stimulate antibody generation....
s of the virus, and may help it evade the immune system. This process may lead to a loss of immunity, or in vaccine mismatch when one of the strains selected for the vaccine doesn't optimally match the circulating strains. Antigenic drift may also allow a virus to jump to a new host species.

he influenza virus, the two relevant genes are the surface proteins, hemagglutinin
Hemagglutinin

Influenza hemagglutinin or haemagglutinin is a type of hemagglutinin found on the surface of the influenza viruses. It is an antigenic glycoprotein....
 and neuraminidase
Neuraminidase

Neuraminidase enzymes are glycoside hydrolase enzymes which cleave the glycosidic linkages of neuraminic acid. Neuraminidase enzymes are a large family, found in a range of organisms....
.






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Antigenic drift is the process of random accumulation of mutations in viral genes recognized by the immune system
Immune system

An immune system is a collection of biological processes within an organism that protects against disease by identifying and killing pathogens and tumour cells....
. Such accumulation may significantly change the antigen
Antigen

An antigen is a substance that prompts the generation of antibodies and can cause an immune response. The word originated from the notion that they can stimulate antibody generation....
s of the virus, and may help it evade the immune system. This process may lead to a loss of immunity, or in vaccine mismatch when one of the strains selected for the vaccine doesn't optimally match the circulating strains. Antigenic drift may also allow a virus to jump to a new host species.

In influenza viruses

In the influenza virus, the two relevant genes are the surface proteins, hemagglutinin
Hemagglutinin

Influenza hemagglutinin or haemagglutinin is a type of hemagglutinin found on the surface of the influenza viruses. It is an antigenic glycoprotein....
 and neuraminidase
Neuraminidase

Neuraminidase enzymes are glycoside hydrolase enzymes which cleave the glycosidic linkages of neuraminic acid. Neuraminidase enzymes are a large family, found in a range of organisms....
. The hemagglutinin is responsible for entry into host epithelial cells while the neuraminidase is involved in the process of new virions budding out of host cells. The host immune response to viral infection is largely determined by the immune system's recognition of these influenza antigens. Vaccine mismatch is a potentially serious problem. Antigenic Drift is continuous process of genetic change among flu strains.

As in all RNA viruses, mutations in influenza occur frequently because the virus' RNA polymerase has no proofreading mechanism, providing a strong source of mutations. Mutations in the surface proteins allow the virus to elude some host immunity
Immunity (medical)

Immunity is a medical term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion....
, and the numbers and locations of these mutations that confer the greatest amount of immune escape has been an important topic of study for over a decade.

Antigenic drift has been responsible for heavier-than-normal flu season
Flu season

Flu season is regularly re-occuring time period characterised by the prevalance of outbreaks of influenza. The season occurs during the cold half of the year in each hemisphere....
s in the past, like the outbreak of influenza A Fujian (H3N2) in the 2003 - 2004 flu season. All influenza viruses experience some form of antigenic drift, but it is most pronounced in the influenza A virus.

Antigenic drift should not be confused with antigenic shift
Antigenic shift

Antigenic shift is the process by which at least two different strains of a virus, , especially influenza, combine to form a new subtype having a mixture of the surface antigens of the two original strains....
, which refers to a more abrupt change in the antigenes. As well, it is different from random genetic drift which is a very different but important process in population genetics
Population genetics

Population genetics is the study of the allele frequency distribution and change under the influence of the four evolutionary processes: natural selection, genetic drift, mutation and gene flow....
.

See also

  • Antigenic shift
    Antigenic shift

    Antigenic shift is the process by which at least two different strains of a virus, , especially influenza, combine to form a new subtype having a mixture of the surface antigens of the two original strains....


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