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Antigenic Shift and Drift
The flu virus has the unique ability to change in two different ways, causing genetic shift and drift. Learn exactly how these two mechanisms differ from one another
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- So what is the difference between an A virus and a B virus? besides A's are able to shift.(5 votes)
- Type A mutates faster than type B does.
You can also watch: http://www.khanacademy.org/partner-content/stanford-medicine/stanford-influenza/v/flu-pathophysiology to learn how they are named.(5 votes)
- In Flu Pathophysiology we learnt that there are only 7 H and 10 N-proteinvariants for flu type A. That makes just 70 combinations. Couldn't we just create them all in Petri-dishes, infect some chimps and develop vaccines for all of them, then vaccinate everybody, and that way eradicate flu type A?(4 votes)
- I think the humans are fooled into thinking we can prevent all kinds of illnesses - - Disease is a control mechanism for the population. Besides clean eating, frequent exercise and other good habits help to keep your immune system strong to help you fight off what ever you get since there is NO WAY we can create a vaccine for everything(2 votes)
- How do the memory cells recognize all these viruses?(3 votes)
- Isn't H1N1 the swine flu?(1 vote)
- Is it likely that a common influenza vaccine (often including 3 strains) can be effective against a shift like this? It sounds unlikely, but I haven't got a clue.(1 vote)
- No. It's similar to the problem we are running into with antibiotic resistance.(1 vote)
- Why B virus can't do shift?(1 vote)
- I think they could if 2 type B viruses got into the same cell. you would get purebred daughter viruses and hybrid ones.(1 vote)
- I'm not sure if i missed it earlier in the video but you say something about RNA at ~3:36. What is RNA?(1 vote)
- RNA is Ribonucleic Acid and is similar to DNA except it is single-stranded and is used mainly for the transmission of genetic code for proteins.(1 vote)
- At1:06what type of small mutations would they be that cause Influenza's antigenic drift ?(1 vote)
- is antigenic drift and shift only in the influenza virus? doing a paper over why a pandemic is inevitable and this is one of my key point(1 vote)
- What does for example H5 stand for?(0 votes)
- you cant name it as H5 alone. For example H5N2 is a proper designation or name for a virus. Because H(hemagglutinin ) and N (neuraminidase) are the proteins that are present on the surface of the virus.(7 votes)
Video transcript
If you remember from a
previous module, we talked briefly how influenza
viruses are categorized and named according to differences
in their genetic material. So what are the processes
by which these influenza genomes becomes so different? It happens in two ways known antigenic
shift and antigenic drift. Let's imagine an
experiment where we look at genetic change over time.
My x axis I have time. On my y axis I'm looking at
genetic change. In this experiment we take an influenza virus,
and we're going to freeze it so we're not allowing
it replicate at all. As a result we have no
genetic change over time. Let's take a second
influenza virus and this time we will allow it to infect
a cell and replicate. As it replicates it's
going to copy its genome which for influenza
viruses is made out of RNA. As it's genome is copied
over and over again it's going to make these small mutations. We see an accumulation of
genetic change over time. This is especially true for
RNA viruses like influenza, because RNA doesn't have
a proof reading mechanism like we have in our DNA
genome which prevents these mutations from occurring. This process is called
antigenic drift. This can happen for all kinds of
viruses not just influenza. What is unique to
influenza A viruses is the ability to undergo huge
amounts of genetic change in a short amount of time.
Let's take an influenza virus in yellow, and
same as before, we let it infect a cell with some
other influenza A strains, and go replicating and
all of a sudden we see a huge jump in genetic
change. Then it might go on replicating as same as
before it's accumulating these mutations, because it's undergoing antigenic drift just like
we saw in the other virus. Then maybe again we see
a huge change in genetic material. These huge
changes are much bigger than just a bunch of point
mutations here and there. This is an entire section
of the genome that's changing, right. This is
what we call antigenic shift. This is really a special characteristic of influenza type A viruses. As I mentioned before,
influenza A viruses can undergo antigenic drift as
well as antigenic shift. Influenza B viruses on
the other hands can only undergo antigenic drift
same as any other virus can. Let me explain in greater
detail what's happening with antigenic shift. Let's
take 2 influenza A viruses. If you remember from a
previous module we talked about how influenza A
viruses are named according to the difference surface
proteins that they have. We're going to call this
one H1N1. We're going to call this one H5N2. It's
got H5 surface proteins, and N2 surface proteins.
It's makes influenza viruses so unique is the
fact that their genome is segmented into 8 pieces. I'm drawing 8 pieces of RNA in
each of these influenza A viruses. Let's say that these 2
different strains of influenza A infect the same cell. When they infect the
same cell they have the opportunity to shuffle their
genetic material around. All of the RNAP pieces from
both influenza A viruses are now in the same cell
and a new virus is produced. This new virus can have
genetic material from each of the parent viruses. In this situation this
new virus, we're going to say it has the H5
surface proteins, and the N1 surface proteins.
This is an H5N1 virus. It got the H5 surface
protein from this parent virus, and it got the N1
surface protein from that parent virus. This is a
brand new influenza virus with new surface proteins
that our immune system has never seen before.
When antigen shift occurs in a population, this is
when we have huge pandemics. The human population isn't
able to defend appropriately against this new virus. That's the story with
antigenic shift and drift . It's definitely an important
one, because it shows how influenza viruses can
potential be so dangerous.