Genetic shift in flu
So we've talked about how influenza viruses attack cells. But every once in awhile, it's really, really unfortunate, but you'll actually get two viruses that affect the same cell. So imagine how bad you'd feel in that situation. Not only did you get sick from one virus, you actually picked up two. So this can happen in humans. It can happen in other animals, like pigs, as well. And it's really just dumb luck when this happens. It's not like it's a coordinated attack. This is just, by random chance, two viruses are going to want to attack simultaneously. So in the top one, let's say we've got some RNA. I'm going to put eight strands of RNA in red. And it's going to code for little H proteins. This is-- I'm going to name it H-- I don't know-- H3. And I'll do one more hemagglutinin protein here. And remember, it looks like a hand because it holds onto sialic acid. And you've got some neuraminidase over here. Neuraminidase is going to nick that sialic acid. It's going to help that virus exit. And let's say this is N2. So we've got H3N2 as the top virus. And in the bottom virus, I'm going to do, let's say, 5, 6, 7, 8. I'm going to do a slightly different color. This is also an H protein, but this is going to be H1, OK? So this is H1, and I'm using the color to try to help you identify them as being different. And we, of course, have some neuraminidase on this virus as well. And this neuraminidase is green. And let's assume that that is N1. So we've got H1N1 on the bottom. And we've got H3N2 on the top. And these two viruses are ready to go. They're ready to attack this cell. And this cell, of course, before these viruses are coming along, it's doing its normal, routine things. It has DNA. But once these viruses get in there, they basically take over. So the virus RNA gets inside. We've got some of the red RNA there. We've got some of the blue RNA here. And so that RNA starts taking over and commands the cell to make more copies of itself. So all of a sudden, the cell becomes a factory for the blue virus, the blue RNA virus. That's the H1N1. It also becomes a factory for the top virus, the H3N2. They just basically both take over together. And so this cell is torn two ways, doing a job for the two different viruses. And this red RNA is actually coding for things like H3. This is a protein down here it's making. And it's also coding for N2. So you've got N2 here, more N2 protein over here. And on the other side, on the top side, you've got some H1 being made. So two different types of hemagglutinin and proteins are being made at the same time in this cell. And of course, you've got two different types of neuraminidase. You've got some N1 being made over here as well. So this is basically what we see. We see the cell making a lot of protein and RNA. And eventually, this cell is going to start sending out little viruses. And that's what I have on the right side. We have the viruses that are exiting the cell. And what do they look like? I guess that's the question. Well, some of them might actually look exactly like the parents. Like If it actually gets all the same red RNA or the same blue RNA, then it might actually look identical to the parents. It might even pick up the exact same proteins. It might have these purple H3's. It might have some purple H3's. It might have some N2 over here. So, actually, this one looks basically the same as its parent. H3N2 is what we would call this one if we were to name it. And this bottom one, the blue one, actually would look potentially the same as well. This might have some H1 over there, maybe some H1 on this side. And it might also have some N1, right? It might have some neuraminidase over there and there. So if I was to name this bottom one, I would actually name it the same thing. I would name it H1N1. But the interesting thing is that, actually, once in a while, you get some mixing. You might get some mixing happening. Maybe you get a couple of blue strands over here, maybe three blue strands. Maybe you get two blue strands over there. And when you get mixing of the RNA, you might also get some mixing of the protein. You might get some protein over here. That's actually H3 and maybe an H3 over here. And maybe on the bottom one, you'll actually get something different. Maybe on this one, you get an H1, maybe an H over here. So you get some mixing of the H's. And maybe on this side you get an N2, maybe an N2. And of course, that wasn't what the parents looked like, right? And up here maybe you get an N1. So, all of a sudden, things are looking a little different. And If I was to name these viruses that are coming out, these progeny viruses, this top one, this would be an H3 because it's got a purple-looking looking hemagglutinin. And it's a green-looking pair of scissors, and that was the N1 protein, right. So that would be an H3N1. And this bottom one over here, this would be an H1, because that's the yellow-colored hand. And the orange pair of scissors, we said that was N2. So, these are actually quite different. So these are different than the parents, right? And the other ones are the same. So when you have different viruses coming out, what does that mean? Well, if the virus is successful-- let's say this one is really successful at getting people sick, and it transmits from one person to another person really effectively. In fact, maybe the first person gets a few people sick because it's so, so contagious. Maybe a lot of people can get sick from just one person being sick. And of course, that's going to spread in all directions, right? Well, that's going to cause many, many, many people to get sick. And we would say, wow, in this population of people, in this community, H3N1 seems to be the dominant new virus. And that process is called genetic shift. So this process of a new virus emerging after shuffling up its genes is called genetic shift. So that's what people talk about. And this, of course, happens with type A viruses. So, remember, we have type A, B, and C viruses. And this is a process that really affects type A viruses only. Now, sometimes you might get the other possibility. Maybe this will come out, and it becomes kind of a dud. It doesn't really affect too many people. It's not very good at causing disease. And if that's the case, it would soon be forgotten. So this mixing, this genetic shifting, can happen in people. You might have a person that's affected by two viruses. And that person would then turn around and perhaps affect other people. Or it can actually happen in animals. You might actually see this happening in pigs. So there might be a little pig here that gets sick. And this pig then would transmit the disease to maybe the farmer. And sometimes you might hear the term "mixing vessel." And there, the mixing vessel refers to whether it was a human, which was case number one, or a pig, which was case number two, in which the actual mixing of the two type A viruses happened.