Health and medicine
- What is the flu?
- Catching and spreading the flu
- When flu viruses attack!
- Three types of flu
- Naming the flu: H-something, N-something
- Testing for the flu
- Antiviral drugs for the flu
- Genetic shift in flu
- Flu vaccine efficacy
- Flu shift and drift
- Two flu vaccines (TIV and LAIV)
- Flu vaccine risks and benefits
- Making flu vaccine each year
- 5 common flu vaccine excuses
- Vaccines and the autism myth - part 1
- Vaccines and the autism myth - part 2
- Flu surveillance
Learn about the three types of influenza virus (Type A, Type B, and Type C) and what makes them differ from one another. Rishi is a pediatric infectious disease physician and works at Khan Academy. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Rishi Desai.
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- Why would there be more people sick when it is colder? would there be less germs out there because it's cold or does this have to do with your body trying to keep yourself warm, so your body can't fight off the germs?(12 votes)
- Well mostly because the air in winter is more stable and viruses are better in colder and dry weather or indoors. and same in school because it's mostly cold sometimes and it's also cold outside. And again because of that you can get higher rates in those months because people are in schools, subways, planes, buses all year round. and again because more people all inside and compacted into areas such as school they will get sick then pass it onto their family then the cycle is then complete and stops because it becomes hotter and and damp (like in the south-east part of America like Florida you will not see rates go up much in winter) the air then would not be as stable as it was in winter. then the cycle restarts in winter in the upper parts of America.(15 votes)
- At1:14, Mr. Rishi says that it is very hard to know whether I have type A flu or type B flu. So why do we have A and B types? Can't there be only one for these two?(4 votes)
- The mutation rate and genetic shift are stronger in type A, which means you can get pandemics, and you get animal flus passed to humans. It's also harder to fight type A with vaccines, because you need to keep changing the vaccine. So the A and B categories are important for that. But there are also differences in the structure of the virus.(8 votes)
- All type A,B and C must have a name.Please comment if you know!(3 votes)
- I don't think there are any names for the types of Influenza. Their viruses just have minor differences like size of their parts and no. of protein chemicals which is why there is no significance of nomenclature.
Source:Structure, properties, and sub type nomenclature, http://en.wikipedia.org/wiki/Influenza(3 votes)
- How is the chance of getting the FLU higher in cold weather? Khan I think you should do a video mainly on that.(2 votes)
- Why are flu epidemics so predictable? Is it due to people spending more time inside?(2 votes)
- and the other way, but how do they spread it if they stay inside. i guess it's just logic, there's nothing unexpected or waiting to caught you out of guard,but i believe it isn't the case,because they mutate(1 vote)
- At7:26it mentions that animals that people are around can be affected by the virus. Would cats, bunnies, or goats be affected too? I'm just curious to know since they are all within the same category of birds, pigs, horses and dogs.(2 votes)
- Influenza virus A can infect a variety of animals as well as humans, and its natural host or reservoir is birds, whereas influenza viruses B, C, and D do not have animal reservoirs
"Influenza A viruses are found in humans and animals, whereas B and C strains infect only humans"
animal influenza viruses: https://www.cdc.gov/flu/other/index.html
- are there specific names for type A,B and C? if so, what is it?(2 votes)
- I'm almost definite that there are no specific names for type A, B, and C. It's kind of like a blood type. If you have type A positive, it's just that. Not the science version. If I am wrong, please correct me.(1 vote)
- Why would there be more people sick when it is colder? would there be less germs out there because it's cold or does this have to do with your body trying to keep yourself warm, so your body can't fight off the germs?Does germs increase when it gets hotter?(2 votes)
- Some scientist tested how well the cells that line mouse airways fought off the virus at different temperatures, finding that cooler temperatures meant a more sluggish immune response and a greater susceptibility to infection.
This website had more information.
- At3:45, does Rishi mean epidemic or endemic? Because there is a flu epidemic during the winter, therefore wouldn't the epidemic be endemic?(1 vote)
- If a problem is endemic in a population, then it is always present. A common example is malaria. It is in mosquitoes and some people are carrying it so it continues to persist in the region. Typically an epidemic is an outbreak of a disease that is sudden and severe in a region. The population was free of it, but suddenly there is a large outbreak and many people are obviously ill. A pandemic is an illness that crosses national borders. The flu is a good example of an illness that is a different epidemic every year. We fight it and overcome it so no one in the population has the disease. Then a new and different virus emerges from say an Asian country and it eventually comes into the county you are in. Suddenly many are sick from this new flu epidemic. Over a few months, the population is sick but then recovers and becomes free of the disease again . It does not remain in the region.(2 votes)
- can influenza virus become immune to anti-bio tics?(1 vote)
- Antibiotics would not be effective against a virus in the first place; they are only effective against bacteria.(2 votes)
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 systematically. So the first thing I want to talk about are the symptoms. If you actually get these types of influenza, what are the symptoms you would expect? Well, for type A you expect the classic things that we talk 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. Constit. And that would be something like a fever or a malaise or body ache. Something like that. And for type B, it's actually pretty much the same. Sometimes people say 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 the classic way we think about flu. Respiratory symptoms and constitutional symptoms. Now, type C is actually kind of different. It's actually usually only respiratory symptoms. Now, of course I'm not going to use the word always whenever I do this kind of thing because everyone can find an example of an exception. But type C is usually going to be just a respiratory symptom. It's usually more mild. So you might have a stuffy nose and 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. As I go through I'm going to kind of circle some things 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. And we would actually-- if someone had a runny nose and a sore throat-- I would think that they had the common cold. So here I'm getting tricked again. 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 actually just draw out quickly the idea of an epidemic 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. This is the calendar year. Now, if I'm thinking of type A or B, I would actually probably expect something like this. Where you have a high level of activity in the winter. And then in the summer it 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 in a red color. Usually you have 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 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 than the baseline. It rises away from the baseline and then it 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 type C is not. And this actually makes sense because with the vaccine you're really worried about people who are going to get very sick. 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 an interesting and important fact about influenza. And what about the idea of genetic drift? And this alludes to the idea of mutations building up. 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 all three of them actually-- they mutate at a different rate. So interestingly, the mutation rate is lowest for type C and highest for type A. So type A has the highest mutation rate. So this is the mutation rate 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 shuffling bits of RNA, or pieces of that genetic material around when two viruses infect the same cell. And we know that this is a major issue when 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 what we always worry about, right? We don't want a virus or an influenza virus to just 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 past 100 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. 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 jump 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 A's. 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 regularly deal with or are around. So farmers might be around pigs. And if you're into horse riding you might be around horses. Many of us have dogs. And birds are 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 an important point and it really goes together with this idea of genetic shift and pandemics. Because you remember you can get all this shuffling of genes that happened 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 goes together.