Three types of flu

let's talk about influenza viruses and the three different types of influenza that there are there are actually three types or three families I think of them as and we're going to go through each family and we're going to talk about the differences between them and so let's actually just label the type over here there's Type A and this is the most common type you usually hear about and type B and C I think are less often talked about but we're going to go through them kind of systematically so the first thing I want to talk about are the symptoms you know if you actually get these types of influenza what are the symptoms you would expect well for type A you expect kind of the classic things that we talked about with flu some respiratory symptom like maybe a cough and also some constitutional symptom I'm just going to write constitutional kind of a short form constant and that would be something like a fever or a malaise or body aches something like that and for Type B it's actually pretty much the same sometimes people say you know type B is a little bit more mild than type A but generally speaking it's very hard to know whether you have type A or type B flu so these are the first two right these are kind of the classic way we think about flu respiratory symptoms and constitutional symptoms right now type C is actually kind of different it's actually usually only respiratory symptoms now of course I'm not I'm not going to use the word always whenever I do this kind of thing because you know everyone can find an example of an exception but type C is usually going to be just a respiratory symptom and it's usually more mild right so you might have a stuffy nose in a sore throat but you wouldn't have the other things you wouldn't have any of the fever the malaise body aches none of that kind of stuff usually so that's one key difference right and actually as I go through I'm going to kind of circle some things that I think are kind of interesting and this is to me very interesting because here we have an example of influenza type C that's actually causing symptoms that we don't classically think of as flu I mean we would actually have someone had a runny nose in a sore throat I would think that they had the common cold so here I'm getting kind of again right so initially we talked about how you have copycat viruses but here's an example of the opposite where the influenza virus actually isn't even causing what I would clinically call the flu so what's another difference between these three types that we have listed here let me actually write out the term epidemic and you may not be totally comfortable with what this word means and sometimes people use the word differently so I'm going to mention what I mean but type A and type B can both cause epidemics and type C really doesn't and what I mean when I say epidemic let me ask you just kind of draw out quickly the idea of an epidemic kind of in my mind let's say you have one year at the bottom January February March April May I'm going to go through the whole calendar year this will be June and July and then August September October November December right this is the calendar year now if I'm thinking of type A or B I would actually probably expect something like this where now you have a high level of activity in the winter and then in the summer it kind of goes down and then as the winter months approach again you see the activity go up and so this would be type A and type B now with type C it's actually really different so type C I'm going to do it a red color usually you have kind of a low level of activity all throughout the year so it doesn't really change a lot so when I say epidemic what I'm really kind of referring to is the fact that you can see that there's an elevation in terms of the number of cases this is number of cases you're seeing more cases during some months of the year then the baseline right it kind of Rises away from the baseline and then it kind of dips down in the summer months so whenever you see more cases than you would expect we sometimes think of that as an epidemic and in this case you might even call it a winter epidemic so type A and B cause these winter epidemics where more people get sick and type C doesn't usually do that now we haven't talked a whole lot about it but what about vaccine which of these influenza viruses can you find in the vaccine well type A is in the vaccine and so is type B but types is not and this actually makes sense because with the vaccine you're really worried about people who are going to get very sick right so these are people that have fevers and malaise and these are the people that are probably going to go on to get more sick because it's a more severe disease and again you want to prevent as much disease as possible so this is the epidemics that you're trying to prevent so it makes sense that type A and type B are in the vaccine whereas type C is not so let me circle that because I think that's also kind of an interesting and important fact about influenza now what about the idea of genetic drift genetic drift and this kind of alludes to the idea of mutations kind of building up right and all three types a B and C all have mutations from time to time that causes changes in the way the virus actually looks to your immune system so the proteins might change a little bit and ultimately if I'm actually they mutate at a different rate so kind of interestingly the mutation rate is lowest for type C and highest for type A so type A is the highest mutation rate so this is the mutation rate kind of creeping up and it's interesting that it's actually quite high for type A which is again that's one of the ones that's in the vaccine remember and alongside genetic drift I want to mention the other one remember we talked about genetic drift and genetic shift and this actually is more about kind of shuffling bits of RNA or pieces of that kind of genetic material around when two viruses infect the same cell and we know that this is a major issue and we think of type A but this doesn't really happen in any clinically significant way for type B or type C it's not a major issue for those types but it is a major issue for type A and next to genetic shift let me write pandemic because this is kind of what we always worry about right we don't want a virus or an influenza virus to just kind of rip through a population and cause massive massive numbers of deaths and hospitalizations and again that is a concern with type A we've seen it many times in the in the past hundred years or so with type A and that's not a concern with type B or C and it's related of course directly to genetic shift right and finally the last category I want to write up is animals we know all three types of influenza are going to affect humans but which ones actually affect animals as well now type A this is the one that affects tons and tons of animals in fact birds are probably the one that jumped to mind you always hear these words like avian flu swine flu right that has to do with pigs and there's actually also horses can get some of these type ace dogs can get them so lots and lots of animals are affected and I want to point out that all these animals I'm writing up here are animals that humans kind of regularly deal with or around right so farmers might be around pigs and you know if you're into horse riding you might be around horses many of us have dogs and birds are kind of flying above us all the time and by comparison there really aren't any animals that humans are regularly in contact with that get type B so that's not really an issue animals are not an issue for type B and for type C there are a couple of animals here I can mention pigs dogs it's not as big a deal as it is for Type A so really type A this is kind of an important point and it really goes together with this idea of genetic shift and pandemics because you remember you can get all this kind of shuffling of genes that happen between birds and pigs and humans and that's sometimes what sets up genetic shift and of course if that happens you might have a pandemic so it all kind of goes together