Animal Viruses: Antigenic Drift vs. Antigenic Shift - Online Tutor, Practice Problems & Exam Prep

Antigenic drift and antigenic shift are crucial concepts in understanding RNA viruses. Antigenic drift occurs due to the lack of proofreading ability in the RNA-dependent RNA polymerase, leading to mutations that allow viruses, like the influenza virus, to evade immune responses. In contrast, antigenic shift involves the mixing of RNA from different viruses, creating new subtypes. This genetic variation is significant for vaccine development, as it necessitates annual updates to flu vaccines to maintain effectiveness against evolving strains.

Animal Viruses: Antigenic Drift vs. Antigenic Shift

In this video, we're going to continue to talk about animal viruses and animal virus infections by specifically focusing on antigenic drift and antigenic shift. And so first we need to recall from some of our previous lesson videos that the enzyme replicase, which, remember, is an RNA-dependent RNA polymerase used by RNA viruses, actually has no proofreading ability. And so recall from some of our previous lesson videos that proofreading is an ability used by polymerases to fix any mistakes that it may have made and to avoid mutations. However, the enzyme replicase has no proofreading ability, which means that it's going to allow for mutations to accumulate over time. And this accumulation of mutations over time can lead to what is known as antigenic drift. Antigenic drift is really just genetic variations or genetic changes over time that result from mutations caused by a lack of proofreading ability in the enzyme replicase. Over time these genetic variations, these genetic changes can result in phenotypic changes or the changes of observable characteristics and traits in the virus. This antigenic drift can allow viruses to avoid the immune system responses by a host cell, allowing the virus to adapt and to reproduce at a more effective rate. Antigenic drift is part of the reason why it is recommended that you get the flu vaccine every single year, because the influenza virus that causes the flu is actually an RNA virus. The replicase enzyme, which lacks proofreading ability, allows for mutations to accumulate in the influenza virus, leading to genetic variations, and so the flu virus is able to avoid the immune response over time. And so that's why we need updated flu vaccines every year to protect us from the influenza virus, which changes due to antigenic drift. And so if we take a look at our image down below over here on the left-hand side, it's focusing on antigenic drift. Notice over here on the left-hand side, we're showing you a virus, and this is virus A. This is an RNA virus, and over time, the replicase enzyme, which does not have proofreading ability, allows for the accumulation of mutations over time. You can see that virus A accumulates mutations, and this mutation right here, you can see here is in red. This changes virus A to become a different strain of the virus, virus B. The characteristics that result from this mutation can allow this virus to avoid host immune responses. Antigenic drift is really just changes, genetic changes in the virus due to mutations over time. Now, in addition to antigenic drift, there's also something known as antigenic shift. Antigenic shift is going to result from the formation of a new virus subtype that has RNA from multiple viruses. If we take a look at our image down below, notice we're focusing on antigenic shift. Notice that we actually have two RNA viruses here; we have virus A and we have virus B. If virus A and virus B infect the same cell at the same time and enter the host cell at the same time, what can happen occasionally is the mixing of the RNA from the two viruses to create a new virus that we have here, which is virus C. Notice that the new virus has some RNA here that was originating from virus A, and it also has some RNA here that was originating from virus B. The mixing of the RNA creates a new virus and we call this antigenic shift. This here concludes our brief introduction to antigenic drift and antigenic shift, and we'll be able to get some practice applying these concepts and learn more about animal viruses as we move forward in our course. So I'll see you all in our next video.

Which of the following is a major difference between antigenic drift and antigenic shift in viruses?

• A. Antigenic drift results from mutations in the viral genome. Antigenic shift results from combining viral genomes.
• B. Antigenic drift results in the deactivation of the virus while antigenic shift results in the reactivation of the virus.
• C. Antigenic drift results in a new subtype of virus being created while antigenic shift does not.

What is the major cause of antigenic drift?

• A. The mixing of RNA viral genomes from two different viruses.
• B. The mixing of viral proteins to form an entirely new virus.
• C. Mutations in RNA viral genomes caused by the replicase enzyme.
• D. Mutations in DNA viral genomes caused by the replicase enzyme.

Here’s what students ask on this topic:

What is the difference between antigenic drift and antigenic shift in RNA viruses?

Antigenic drift and antigenic shift are mechanisms of genetic variation in RNA viruses. Antigenic drift occurs due to the lack of proofreading ability in the RNA-dependent RNA polymerase (replicase), leading to the accumulation of mutations over time. These mutations result in genetic changes that allow the virus to evade the host's immune response. In contrast, antigenic shift involves the mixing of RNA from different viruses when they infect the same host cell simultaneously. This mixing creates a new virus subtype with RNA segments from multiple viruses, leading to significant genetic variation. Both mechanisms are crucial for understanding the evolution of viruses like the influenza virus and the need for annual updates to flu vaccines.

Why is it necessary to get a flu vaccine every year?

It is necessary to get a flu vaccine every year primarily due to antigenic drift in the influenza virus. The enzyme replicase, which the influenza virus uses for replication, lacks proofreading ability, leading to the accumulation of mutations over time. These mutations cause genetic variations that allow the virus to evade the immune system. As a result, the flu virus changes from year to year, necessitating updated vaccines to provide effective protection against the most current strains. Annual vaccination helps ensure that the immune system can recognize and combat the evolving virus effectively.

How does antigenic drift contribute to the evolution of viruses?

Antigenic drift contributes to the evolution of viruses by allowing genetic variations to accumulate over time due to the lack of proofreading ability in the RNA-dependent RNA polymerase (replicase). These mutations can lead to changes in the virus's observable characteristics (phenotypes), enabling it to evade the host's immune response. This continuous genetic variation allows the virus to adapt to new environments and hosts, enhancing its ability to survive and reproduce. In the case of the influenza virus, antigenic drift is a key factor in the virus's ability to change and necessitates the development of new vaccines annually.

What role does the enzyme replicase play in antigenic drift?

The enzyme replicase, an RNA-dependent RNA polymerase used by RNA viruses, plays a crucial role in antigenic drift. Unlike DNA polymerases, replicase lacks proofreading ability, meaning it cannot correct errors that occur during RNA replication. As a result, mutations accumulate over time in the viral genome. These genetic changes can lead to variations in the virus's surface proteins, allowing it to evade the host's immune response. This process of gradual genetic change due to accumulated mutations is known as antigenic drift and is a significant factor in the evolution and adaptability of RNA viruses like the influenza virus.

How does antigenic shift lead to the creation of new virus subtypes?

Antigenic shift leads to the creation of new virus subtypes through the mixing of RNA from different viruses. When two different RNA viruses infect the same host cell simultaneously, their RNA segments can mix and reassort. This process results in the formation of a new virus subtype that contains RNA from both original viruses. The new virus has a unique combination of genetic material, which can lead to significant changes in its characteristics and behavior. Antigenic shift is particularly important in the context of influenza viruses, as it can result in the emergence of new strains with pandemic potential.