Differences Between Antigenic Shift and Antigenic Drift

 

Differences Between Antigenic Shift and Antigenic Drift

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S.N.	Characteristics	Antigenic Shift	Antigenic Drift
1.	Definition	Antigenic shift refers to the gene recombination occurring when influenza viruses re-assort.	Mutations causing minute changes in the hemagglutinin and neuraminidase antigens on the surface of the Influenza virus is termed antigenic drift.
2.	Result in	Forms a new sub-type (Subtype A + Subtype B –> New Subtype).	Forms a new strain of the virus.
3.	Genome changes	Large change in nucleotides of RNA.	Small mutation of RNA.
4.	Results from	Genome re-assortment between different subtypes.	Accumulation of point mutations in the gene.
5.	Change type	The change is sudden and drastic.	The change is gradual.
6.	Virus involved	One or more viruses are involved.	Only one virus is involved.
7.	Magnitude of change	The change is large at once.	Changes increase with each division cycle.
8.	Relatedness of new virus	The new form or subtype produced bears no similarity to the previous virus.	The strains produced by antigenic drift are somewhat similar to the older strains.
9.	Host range	May jump from one species to another, for instance, animal to human.	May infect animals of the same species only.
10.	Frequency of occurrence	Occurs once in a time.	Occurs frequently.
11.	Antigen changes	The virus acquires completely new antigens—for example by reassortment between avian strains and human strains.	Antigens are only mutated.
12.	Virus type involved	Occurs only in Influenza Virus A	Occurs in Influenza Virus A, B, and C
13.	Leads to	Leads to pandemics.	Leads to main epidemics.
14.	Treatment option	Difficult to treat (need new vaccine)	Easy to treat (antibody and drugs available)
15.	Susceptibility	Everybody is susceptible to the virus after an antigenic shift, and novel influenza may thus spread uncontrollably.	Some people may still be immune and some others may be partially immune to the new strain of virus thus leading to a milder illness.
16.	Examples	The 1968 pandemic arose when the H3 hemagglutinin gene and one other internal gene from an avian donor reassorted with the N2 neuraminidase and five other genes from the H2N2 human strain that had been in circulation. The 1918 pandemic arose when an avian H1N1 strain mutated to enable its rapid and efficient transfer from human to human.	The subtle mutations accumulated through antigenic drift of these subtypes (e.g., H1N1, H3N2, H5N1) give rise to different strains of each subtype. Antigenic drift is also known to occur in HIV (human immunodeficiency virus), which causes AIDS, and in certain rhinoviruses, which cause common colds in humans. It also has been suspected to occur in some cancer-causing viruses in humans.