The main difference between antigenic drift and antigenic shift is that antigenic drift is a mechanism for variation in viruses by accumulating mutations within genes, which code for antigen-binding sites whereas antigenic shift is a process of combining two types of viruses to form a new subtype with a mixture of surface antigens of the original viruses.
Antigenic drift and antigenic shift are two processes used by viruses to adapt to the selection pressure and avoid host immune systems. Antigenic drift is a minor antigenic change resulting in a new strain of virus while the antigenic shift is a major antigenic change, resulting in a new subtype.
Key Areas Covered
1. What is Antigenic Drift
– Definition, Process, Importance
2. What is Antigenic Shift
– Definition, Process, Importance
3. What are the Similarities Between Antigenic Drift and Antigenic Shift
– Outline of Common Features
4. What is the Difference Between Antigenic Drift and Antigenic Shift
– Comparison of Key Differences
Key Terms
Antigenic Drift, Antigenic Shift, Hemagglutinin, Influenza Viruses, Neuraminidase
What is Antigenic Drift
Antigenic drift is a slow change in the viral genes, occurring due to replication errors or random mutations. Eventually, it results in a new virus strain. Generally, antigenic drift within genes coding for antigen-binding sites inhibits the effectiveness of antibodies produced for the previous antigens. It makes the spread of the virus in the host easier. Therefore, antigenic drift results in the loss of immunity as well as vaccine mismatch.
Figure 1: Antigenic Drift
Furthermore, antigenic drift occurs in Influenzavirus A, B, and C. Basically, Influenza virus contains two proteins, which serve as surface antigens. They are hemagglutinin and neuraminidase. Here, hemagglutinin is responsible for the binding and entry into host epithelial cells while neuraminidase takes part in the process of new virions budding out of host cells. However, the sites on these proteins recognized by the host immune system are under constant selective pressure. Nevertheless, small mutations in these sites by antigenic drift allow evading the host immune system.
What is Antigenic Shift
Antigenic shift is a rapid and large antigenic change in a virus. Generally, it requires two different viral strains to combine to form a new viral subtype. The new subtype of the virus contains a mixture of surface antigens in original strains. Especially, this is a specific type of reassortment, which also confers a phenotypic change.
Figure 2: Antigenic Shift
Moreover, Influenzavirus A is an example of a virus, which undergo an antigenic shift. Normally, it infects not only humans, but also other mammals and birds. Therefore, this virus has a chance to reorganize its surface antigens when two strains of the virus infect the same host simultaneously. Basically, this is by the removal of capsids and envelops, exposing their RNA to undergo transcription. It allows the viruses to combine.
Similarities Between Antigenic Drift and Antigenic Shift
- Antigenic drift and antigenic shift are two mechanisms used by viruses to adapt to the selection pressure and avoid host immune systems.
- Both mechanisms change the pool of antigens in the original virus.
- Thus, the resulting viruses cannot be inhibited well by antibodies against previous strains, making it easier for them to spread throughout a partially immune population.
Difference Between Antigenic Drift and Antigenic Shift
Definition
Antigenic drift refers to a mechanism for variation by viruses, which involves the accumulation of mutations within the antigen-binding sites while antigenic shift refers to a sudden shift in the antigenicity of a virus resulting from the combination of the genomes of two viral strains. Thus, this is the main difference between antigenic drift and antigenic shift.
Mechanism
In antigenic drift, the variation in the antigenic pool is by the accumulation of gene mutations while in an antigenic shift, two different strains of viruses combine to form a new subtype.
Degree of Antigenic Change
Moreover, antigenic drift is a minor antigenic change, while the antigenic shift is a major antigenic change.
Result in
Further, while antigenic drift results in a new viral strain, antigenic shift results in a new subtype of the virus.
Frequency of Occurrence
Also, another difference between antigenic drift and antigenic shift is that antigenic drift frequently occurs while antigenic shift occurs once in a time.
Host variation
New viral strain produced by the antigenic drift may infect the hosts of the same species while the new viral subtype produced by the antigenic shift may infect another host in a different species.
Treatment
Antigenic drift is easy to treat, while antigenic drift is difficult to treat.
Occurrence
Besides, antigenic drift occurs in Influenzavirus A, B, and C while antigenic shift occurs in Influenzavirus A.
Give Rise to
While antigenic drift gives rise to epidemics between pandemics, antigenic shift gives rise to pandemics.
Conclusion
Antigenic drift is a type of minor antigenic change in viruses, occurring due to the accumulation of mutations. Generally, it causes the formation of a new virus strain from the original strain. On the other hand, the antigenic shift is a major antigenic change which occurs due to the combination of two strains of viruses. It also results in a new viral subtype. Therefore, the main difference between antigenic drift and antigenic shift is the type of change in the original virus.
References:
1. “How the Flu Virus Can Change: ‘Drift’ and ‘Shift’ | CDC.” Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases, Available Here.
Image Courtesy:
1. “Antigenic Drift of the Flu Virus” By NIAID (CC BY 2.0) via Flickr
2. “AntigenicShift HiRes vector” By derivative work: MouagipAntigenicShift_HiRes.png: National Institute of Allergy and Infectious Diseases (NIAID). (Public Domain) via Commons Wikimedia
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