Key Difference – Antigenic Drift vs Antigenic Shift
The antigenic structures of the influenza virus change its shape to a new shape which cannot be recognized by the antibodies. Antigenic shift and antigenic drift are two types of genetic variations that occur in influenza virus. These variations make it difficult to prevent common diseases associated with influenza virus by vaccines or the natural immunity system. Main two types of glycoproteins (antigens) named hemagglutinin (H) and neuraminidase (N) located at the outer surface of the virus are modified by the viral genes as a result of antigenic drift or antigenic shift. The key difference between antigenic drift and antigenic shift is that antigenic drift is a genetic variation that occurs in the antigen structures due to a point mutation happens in the genes of the H and M within the viral genome over the year whereas antigenic shift is a variation occurs in the antigenic structures due to a sudden genetic reassortment between two or more closely related influenza viral strains. Both these variations help the influenza virus to overcome host defenses.
CONTENTS
1. Overview and Key Difference
2. What is Antigenic Drift
3. What is Antigenic Shift
4. Side by Side Comparison – Antigenic Drift vs Antigenic Shift
5. Summary
What is Antigenic Drift?
Viruses are electron microscopic small infectious particles which can infect all forms of living organisms including bacteria and plants. They are composed of genetic material and glycoprotein capsid. Viral genome codes glycoproteins (antigens) which are important for attaching to the host organism and include viral genome to replicate within the host organism. Influenza virus is one type of virus responsible for the common cold associated diseases among humans and other animals. It exists in different strains and has a segmented RNA genome, and two prominent antigens (receptors) called H and N on the glycoprotein coat.
Figure 01: Influenza Viral Structure
H and N antigens of the influenza virus bind to the host cell receptors and make a successful infection to cause the disease. H and N antigen structures can be easily recognized by the host defense systems which destroy the viral particles to prevent the disease occurrence. However several genetic variations of influenza viral particles limit the chance of destroying the viral antigens which enter the host body by the host immune system. Antigenic drift is such kind of a genetic variation common in influenza virus. It happens due to gradual development and accumulation of a point mutation in the genes of H and N. As a result of this point mutation, viral particles acquire the capability of changing the H and N antigen structures which cannot be recognized by the host cell antibodies or vaccines. Therefore, the mutations of these H and N coding genes allow the viral particles to escape from the host immune systems and spread the disease.
Antigenic drift in epidemic flues such as H3N2 and the viral strains are capable of infecting new individuals of the same host species to spread the disease easily. This type of genetic variation is more common and frequently occur among the influenza virus strains A and B.
Figure 02: Antigenic Drift
What is Antigenic Shift?
Antigenic shift is another type of genetic variation that occurs in influenza viruses due to the reassortment of genetic materials between two or more similar viral strains. Antigenic shift occurs between closely associated strains. When a host organism is infected with two influenza strains, there is a possibility of exchanging or mixing of genetic materials of the two strains to create a new viral strain with the mixture of genes. This genetic recombination gives the new viral particle a novel capability to escape from the host defense system without recognition. Thus, it is capable of infecting host cells of more than one species and cause a pandemic disease. However, antigenic shift is a rare process which has fewer chances for the occurrence. Influenza virus A can undergo antigenic shift and is capable of infecting a large number of host species, resulting in flu pandemics.
Figure 03: Antigenic Shift
What is the difference between Antigenic Drift and Antigenic Shift?
Antigenic Drift vs Antigenic Shift |
|
| Antigenetic drift is a genetic variation occurring in the viral genome due a development and accumulation of point mutations in the genes that encode H and N. | Antigenetic shift is a variation occurs in the viral genome due to gene reassortment between two or more viral strains. |
| Development of the Genetic Change | |
| Antigenic drift is a gradual change over the years. | Antigenic shift is a sudden change. |
| Genetic Change | |
| It happens due to a point mutation of genes coding for Hemagglutinin and Neuraminidase. | It happens due to the reassortment of genes between two closely related influenza viruses. |
| Flu Strain | |
| This occurs in both influenza A and B. | This occurs only in Influenza A virus. |
| Possibility of Infection | |
| Antigenic drift allows the new viral particle to infect more individuals from the same host species. | Antigenic shift creates a new viral particle which is capable of infecting different species. |
| Occurrence | |
| Antigenic drift is a frequent process in influenza virus. | Antigenic shift is a rare process. |
| Nature of the Disease | |
| This can lead to an epidemic among the population such as H3N2. | This can lead to a pandemic in the population such as H1N1, Spanish flu, and Hong kong flu. |
Summary – Antigenic Drift vs Antigenic Shift
Mutations in the segmented RNA genome of the influenza virus give rise to genetic variations in the viral particles and fight against the host defense mechanism. Antigenic drift and antigenic shift are two kinds of genetic variations that occur in influenza (flu) virus. Antigenic drift is a genetic variation which results from the gradual development of point mutations in the genes of H and N of the virus. Antigenic shift is a genetic variation which results from the genetic material exchange between two or more closely related strains of influenza virus. This is the key difference between antigenic drift and antigenic shift. Both these processes create viral particles which are more virulent than preexisting viruses. Therefore, antigenic drifts and shifts make it difficult to develop vaccines and medications against the flu virus.
References:
1. Bouvier, Nicole M., and Peter Palese. “THE BIOLOGY OF INFLUENZA VIRUSES.” Vaccine. U.S. National Library of Medicine, 12 Sept. 2008. Web. 21 Mar. 2017
2.”Mechanisms of antigenic variation in influenza virus”. Nihon rinsho. Japanese journal of clinical medicine. U.S. National Library of Medicine, n.d. Web. 21 Mar. 2017
3. Boni, Maciej F. “Vaccination and antigenic drift in influenza.” Vaccine. U.S. National Library of Medicine, 18 July 2008. Web. 21 Mar. 2017
Image Courtesy:
1. “3D Influenza virus”By National Institutes of Health; originally uploaded to en.wikipedia by TimVickers (25 October 2006), transferred to Commons by Quadell using CommonsHelper. – California Department of Health Services (Public Domain) via Commons Wikimedia
2. “Antigenic Drift of the Flu Virus” by NIAID (CC BY 2.0) via Flickr
3. “AntigenicShift HiRes vector” By derivative work: MouagipAntigenicShift_HiRes.png: National Institute of Allergy and Infectious Diseases (NIAID). AntigenicShift_HiRes.png (Public Domain) via Commons Wikimedia