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Current time:0:00Total duration:9:54

Naming the flu: H-something, N-something

Video transcript

so we often talk about influenza in terms of letters you I'm sure you've heard of h1n1 or something like that and what I wanted to do is explain where that naming system comes from what it means and how it relates to the three types of influenza that exist a B and C now let's say I went around the world collecting all the different influences I could find it I might find some type C influenza and I find some type B influences as well and I would find probably lots and lots of type aids because there's so much diversity among the A's lots of different types now when you have a few viruses it's fine to say well as a type B or it's a type C but when you have this many viruses like I'm drawing for Type A it becomes a little overwhelming to simply say well it's a Type A because you're probably thinking well there's so many different types tell me more I want to know more about it and so in order to find out more about it or tell someone more about it what people have come up with is a new naming system or kind of a different naming system other than just the letter so what they do is they say okay let's go back to what the virus looks like we know that the the virus has kind of an outside and envelope right that's what I'm drawing here and on the inside the influenza virus has RNA and if it's a type A virus or type B virus that means it has eight chunks of RNA the type C actually has only seven so this one that I drew here this must be a type A or B and I'm going to go ahead and tell you it's a type A and we know that on the outside type A's have some proteins right they have some proteins I'm drawing as kind of a little hand because this is to remind me that it's an H protein or hemagglutinin protein and they also have a type n protein n protein and so type H and type n remember H is hemagglutinin helps the virus get into cells or hold onto psionic acid and type n is neuraminidase and it kind of Nick's the salic acid and helps the virus get out of a cell now scientists have been looking at these proteins for a while and they've actually counted all the different types of H proteins they could find they found that there are about 17 types meaning they all do the same thing they all have the same job but they're slightly different they're protein their structure might be slightly different and if you count up all the different end proteins that are actually only ten so ten different types of n proteins and seventeen types of H proteins now if every virus has to have some H and some n how many different combinations would you get well you simply multiply them right you simply multiply seventeen times ten and that means there are 170 combinations you can actually come up with in terms of different types of HS and ends coming together so if that's the total number then we can use that to actually name the different types of influenza is you can actually say well maybe this guy maybe this guy has the third type of H and the second type of n and if that was the case we call it an h3n2 and maybe this guy has the first type of H and the first type of n and that would be h1n1 and maybe this guy is h5n1 or maybe this is H 7 n 2 I think you get the idea basically you just kind of name them based on the H and the end that they have on the outside now here's something to think about what happens if you actually look at this little virus and you find that this virus has the first H and the first n does that mean that these two are identical are they the same well the answer is no they're not necessarily the same I guess they could be the same right but they may not be the same and you're thinking well why they have the exact same H and n how could they be different well remember that there's a lot of RNA in here right there 8 segments of RNA 8 RNA segments and H and n are just two proteins there are other proteins that this virus has inside of it that might distinguish these two from each other and so if this is the newer one you might say well this is the novel h1n1 to distinguish between the two different viruses so whenever you see words like novel h1n1 now you understand why they're coming up with that name they're just trying to help you distinguish new from old so actually what I did is I went ahead made a grid I made a grid up to H types and the end types all 17 HS and all 10 ends and what I wanted to do is show you that you can actually kind of make this really simple you could say well obviously if you have this first H in this first n then in this grid I would type in h1n1 so there is where this is where h1n1 would go and at the other end of the grid let's say down here you can actually say well this guy down here would be H 17 and 10 and I could do this for all hundred seventy right I could go ahead and name all 170 using this grid so out of these 170 combinations the one that humans care most about are the ones that most commonly affect us and it turns out that h3n2 and h1n1 are two that are dominant in human societies human populations now this wasn't always the case but it at the moment in 2013 that is the case actually back let's say about four or five decades ago a more common one was h2 n2 in fact h2 n2 caused lots and lots of disease many people got sick from h2 n2 and it was a cause of a pandemic but since then h2 n2 has kind of been replaced by these that we see now so I'm going to erase h2 into entirely because nowadays we see more of the h1n1 and h3n2 now why do you suppose that would be the case why would some be more dominant or more common in human populations over others I mean there are so many combinations you could think of right why did these two do such a good job well the answer is that from a virus's perspective if it's trying to get to as many people as possible it's got to do a really good job of transmitting from one sick person to another so that I can spread really really quickly through a whole population and both of these viruses do that they actually spread from person to person really effectively so if you have the flu and we know that it's a Type A I should have written that earlier because this naming system we said is only for type A's if you know you have a Type A flu the chances are pretty high that you have either one of these either h1n1 or h3 and two now with all these other possibilities where do we see all these other H&N viruses well turns out that unfortunately for the birds a lot of these viruses affect them so birds are actually where you find a lot of these viruses so here's my bird and it turns out that almost every virus that we've found can be found in a bird and these are pigeons ducks you know you get the idea there's only one virus actually or one type of h/n combination I should say that you don't really see in birds and that's this one this H 17 and 10 interestingly this one is seen in bats so all the other combinations are seen in birds and in fact not just birds some of these you'll see in let me write out here horses some of them you'll see in pigs you'll see in dogs and and birds as well so a lot of different animals can get these other H n type viruses but again just to stress the point the ones that we see in humans are usually h1n1 or h3n2 now let's say that you do work with birds that's part of your job and one day you actually see that there's a sick bird and unfortunately for you you pick up the flu from it and this could be one of the other H combinations right H n combinations so maybe you pick up h5n1 from this poor sick little bird or maybe pick up h7 into this has all been actually shown that these viruses can spread from birds over to humans and so maybe pick up h7 and 3h9 into there a few of them right if you pick up one of these viruses then you would get sick obviously because you got the flu so it does cause symptoms in humans but the key idea is that at the end of the day it doesn't circulate these viruses don't seem to circulate as well between humans and as a result the dominant viruses still remain these ones that actually do a better job of going from person to person these two human viruses or these two dominant human viruses I'll write dominant because again you can get like with some of the other ones but these are the ones that we most often see in human populations so the last thing I want to mention is the naming structure it gets a little bit fuzzy and confusing because sometimes we actually name things like avian sometimes you might see avian which is another word for bird or you might see swine which is another word for pig so if you hear the terms swine flu or avian flu what do they mean well because RNA pieces get shuffled back and forth between birds and humans and pigs from time to time what they do is they basically try to identify where the genes come from for this particular virus did it come primarily from a bird or from a pig and based on what they find they think okay well let's call it avian flu or let's call it swine flu but honestly I think those terms are very confusing for a lot of people and it's probably easier to just think about them in terms of h's and ends