Articles, Blog

Three types of flu | Infectious diseases | Health & Medicine | Khan Academy

September 28, 2019


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.

49 Comments

  • Reply drppenev January 11, 2013 at 8:10 pm

    Very nice.

  • Reply TheLordShinnok January 23, 2013 at 7:23 am

    A pandemic is very likely to happen and bird flu isweaponized

  • Reply Helen Frey April 28, 2013 at 6:38 am

    Good job. Easy to understand. Appreciate the effort

  • Reply Chris Boggus January 16, 2014 at 1:11 am

    Finally a smart flu video thanks man

  • Reply Kittymewmew1000 April 26, 2014 at 8:18 pm

    Now what if I'm throwing up and have diarrhea? I also have fatigue, body aches and slight chills but zero respritory symptoms

  • Reply The WelshWale October 17, 2015 at 2:46 pm

    there is more there is Asian flu birdflu Spanish flu swine flu stomach flu and more

  • Reply FreakShow91 October 19, 2015 at 1:49 am

    i had type b now i think i have type c

  • Reply Brittney Waters November 19, 2015 at 2:55 pm

    i had type b and b is worse than a

  • Reply Divine Destiny January 21, 2016 at 6:29 am

    Well, lets also mention that the SWINE FLU also has (3) strands in One Virus… Yes, the SWINE FLU was biogenetical developed in a lab.. How do I know this? We'll, I, personally got it in 2009.. I had a temperature of nearly 104, incredibly weak, and literally thought that I would die. My doctor though that it was a good idea to shoot me up with more of the virus, thus it sterilized me!!! Now, I can no longer have kids!!! Do the research and you will learn about "Agenda 21 & Eugenics." There are some very mentally sick people running our planet at this time; AND they are SICKER than I was, because, I AM very well now, despite it all.. I have Almighty Mother/Father God in my life as well as Christ & My Angels.. They said it wasn't my time to go, so I'm here to share my story with you all, that I WILL NEVER TAKE ANOTHER VACCINATION AGAIN.. LIFE OR DEATH.. NEVER.. THEY ARE VERY LETHAL .. AND DESIGNED WITH EVIL INTENTIONS. Infinite, Love, Compassion, & Forgiveness to the Evil-doers on this planet……… & Love, Compassion & Protection to my fellow Brother's & Sister's… The Light of Almighty God shall over-come ALL Darkness of ALL Evil-doers<3

  • Reply Victoria Afolabi Aiyelokun February 28, 2016 at 11:31 pm

    can these happen to teenagers to catch the flu and do they have a cure for all the influenza disease

  • Reply Ahmed-G March 29, 2016 at 5:38 pm

    I was diagnosed with influenza B today. It is a lot worse than A.

  • Reply Wills Pram April 1, 2016 at 4:35 am

    I have the flu right now (Type B), that's why i'm watching this. Haven't slept in days, head hurts too much.

  • Reply Jesus ortiz October 29, 2016 at 2:30 am

    Right now I have flu type A

  • Reply Ali and Mohammed Basheer November 15, 2016 at 7:42 pm

    thanks

  • Reply Ayumi Kawashima December 15, 2016 at 11:21 pm

    Right now ihave the flu type a its horrible I can't move and can't talk can't even go to school

  • Reply G C January 28, 2017 at 4:46 am

    dogs can get the same flu i have a elderly dog just got this week bad

  • Reply infiniteuniversalthinking January 29, 2017 at 10:49 pm

    OMG are you the same guy who does chemistry as well? The voice sounds the same…

  • Reply infiniteuniversalthinking January 29, 2017 at 10:54 pm

    I got alll of them this winter. First I got B, A and now C however I'm finding it hard to breath as the cough is so strong.

  • Reply Sarah Teasley January 30, 2017 at 12:54 pm

    I have influenza type B

  • Reply Amanda Misroame February 17, 2017 at 10:41 am

    i have it now went to stay in hospital for days….

  • Reply monia February 18, 2017 at 3:30 pm

    It won't be a winter epidemic. Since you are expecting the elevation, it would just be an endemic. I think.

  • Reply koki nagashima February 23, 2017 at 4:01 pm

    Guys I have influenza type A but I don't feel anything only the first day but now to at all I fell nothing weird right last year I hade influenza type B and I was very sick but now no

  • Reply Hopewashere March 9, 2017 at 6:12 pm

    I have Flu B right now! Everyone has it at my school and in my area right now!

  • Reply kiwi sister April 4, 2017 at 4:41 pm

    I got flu b right now

  • Reply fathmath Ulya October 6, 2017 at 2:39 pm

    your handwriting is so talented when you are just writing in computer ….

  • Reply Drawings of EggNugg December 30, 2017 at 11:36 pm

    I am fucked I got type A because my Co-woker had a flu and i got the flu from him ughhh

  • Reply Marissa Perez January 6, 2018 at 6:02 am

    I have type A

  • Reply TypicalNinjaGamerKD3 January 13, 2018 at 12:06 am

    I have the flu

  • Reply Auston Allen January 28, 2018 at 2:53 am

    I have type b

  • Reply food islife February 1, 2018 at 5:58 pm

    I have type a….. This is the second time I've had it in my life… Had it the same time last year….first time headache . vomiting.stomach issue and body ache . Now in just stuffy

  • Reply Jacob S. February 2, 2018 at 9:33 pm

    I have Type A…fml

  • Reply Paul Michel February 3, 2018 at 3:04 pm

    Well done, but need more differentiation of type A to type B.

  • Reply ***** February 4, 2018 at 3:23 pm

    Blame Britain we got the bad strains from them

  • Reply ItzLiterallyLondon February 6, 2018 at 8:09 pm

    You said circle not rectangle

  • Reply Di anne February 9, 2018 at 4:38 am

    I had Influenza A last year(Jan2017). High grade fever, cough, green phlegm, sore throat and all that nasty stuff; it was one of the worst!
    Today (Feb2018) I have Influenza B and I am heavily congested, random chills and low grade fever.

    Both times I was advised to stay home for 5 days!!

  • Reply MISSTHANG NAYA February 25, 2018 at 10:15 am

    How can u heal yourself

  • Reply Sweet Tea February 26, 2018 at 11:52 am

    My sis has type A flu but she is acting fine .

  • Reply Ana Bautista February 27, 2018 at 1:51 am

    Type c

  • Reply yan tang March 4, 2018 at 1:27 am

    I got flu b last year

  • Reply Mikail M May 1, 2018 at 4:29 pm

    I have type a

  • Reply Shana Harris September 22, 2018 at 5:25 am

    I have type A

  • Reply Charee Pringle November 7, 2018 at 4:49 pm

    Does flu fit under airborne or droplet precaution

  • Reply alisha hughes January 23, 2019 at 10:00 pm

    Type A

  • Reply Angel Bulldog February 9, 2019 at 2:27 am

    I have type B right now. Almost 70, only 2nd time I've had the flu. NEVER would I take the flu shot. Every vaccine in America contains cancer enzymes. Newborns are getting this, too. Just say NO to vaccines!

  • Reply Sherry Messer February 11, 2019 at 4:00 pm

    So I got Flu A from my new puppy? Because I have not been sick in literally over 15 years, and had no pets at all till recently and then I get my pup… I been sick off and on ever since. Or at least for the past week and my pup is three months old.

  • Reply Sarah Watson February 20, 2019 at 3:40 am

    I have type A right now and feel miserable. I always have a habit of researching what I’m diagnosed with and learning as much about it as possible (Nerd Alert! I know.)

  • Reply Fallen FN March 18, 2019 at 11:49 pm

    I have the worst type a

  • Reply Harneet kaur April 16, 2019 at 4:40 pm

    Hello Khanacademy, first of all, your videos are awesome, beyond any word can describe. I am preparing for Canadian board exams and they are helping me a lot to understand the concept. My only concern is the references. What are the references to these videos? Are they per Canadian medicine guidelines as well? Thank you!

  • Reply Angie Gutierrez August 30, 2019 at 2:00 am

    I got A and B✌️

  • Leave a Reply