How are Viruses Classified?

How are Viruses Classified?


Today I’m going to talk about viruses – what
they are and how they can be classified into a family tree of sorts. Obviously, one particular
virus has been on people’s minds a lot these days and several people asked me to do a video
on this topic using my Evolution & Classification of Life chart. So that’s what I’m going
to do. If you’ve seen my previous video on this particular chart (which I’ll link
to in the description) or if you own a copy of the chart yourself, you’ll notice that
the virus section is located in the bottom right-hand corner. And that’s where we are
going to start. Intro So the first thing you’ll notice is that
everything on this chart – from single celled bacteria to human beings – is located on
one big tree. Everything that is, except viruses. They get their own tree, down here to the
side. That’s because, generally-speaking, they are considered to
be non-living. Hence they are not part of the “tree of life”. Now there’s actually
some debate about this – about how exactly viruses evolved and how exactly they relate
to this big tree over here. Some scientists think that viruses perhaps came first and
that life maybe evolved from viruses. More recently, others scientists have come
to think that perhaps life actually evolved first and that viruses are perhaps some sort
of strange spin-off that occurred at a later point. Either way, we do know that this little
tree actually does somehow connect to this big tree – we just don’t exactly how.
So for now, it’s best to just think of viruses as being something separate – because they
do differ from everything else several very important ways. The most important difference is that life
can replicate by itself. So, let’s take bacteria. Bacteria, like viruses, can make
us sick. But they are very different. They are actually teeny tiny single-celled lifeforms.
If you put a few in a petri dish, they will actually – given the right circumstance
– multiply and form a colony that will continue to grow larger and larger. Viruses cannot do this. Simply put, a virus
cannot replicate or multiply on its own. So if two littles viruses are sitting by themselves
on a counter, you’re never going to get a third one. The two initial ones are going
to just sit there until they die. Or until a living thing comes along and allows them
to hitch a ride. You see, for a virus to multiply, they need to attach themselves to something
living – like a human. Once a virus gets inside a human (or some
other creature), it then IS able to replicate and multiple. And this is why they are just
as dangerous to us as bacteria. So now lets look at how they are classified.
Most scientists use a system called the Baltimore classification, named after an American scientist
named David Baltimore. That system divides viruses into seven different categories using
Roman numerals. This chart only shows some of the main viruses that impact humans and
therefore only 4 of the 7 categories are represented. So viruses don’t have kingdoms, phyla or
classes, like living things. They just have this simple numbers. But then after those
numbers, we do get orders, families, genera, and species. Okay, let’s start with Type I viruses. Type
I viruses are made from double stranded DNA, just like living things are. A good example
of a virus with double stranded DNA is the smallpox virus. Smallpox is the virus that
killed more humans throughout history than any other, including the majority of indigenous
Americans after European contact. But you’ll be happy to know that it no longer exists.
Because of vaccination efforts, it was completely eradicated in 1979. A less serious group of
Type I viruses is the Herpes order of viruses. Included are the types of Herpes that are
transmitted sexually but also chickenpox, a virus that used to be a very common childhood
illness. Type 4 and 5 viruses are the ones that are
made up of standard single-stranded RNA. So, to recap what you probably already learned
in school, DNA is often called the “building blocks of life”. It has this now famous
double helix structure. RNA, on the other hand, usually consists of just a single strand
of genetic material. Now there are actually some exceptions. Type II viruses are actually
made up of single stranded DNA and Type III viruses are actually made up of double stranded
RNA but that subject is way beyond the scope of this video. For our purposes, you can just
remember that DNA has a double strand and RNA has a single strand. But those singe strands can be categorized
as either positive or negative and that’s the difference between Type IV and Type V.
Type IV viruses are positive and Type V are negative. Now, by positive and negative, I
don’t mean good or bad. It just has to do with how the virus attaches itself, kind of
like the positive and negative ends of a battery. So Type IV includes an order called Picornavirales.
Included in this order is the most common virus to infect humans – the rhinovirus.
It’s the virus that causes the common cold. “Rhino” actually comes from the Greek
word for “nose” which is also how the rhinoceros got its name. But the main thing
I want to point out here is that colds are not caused by the influenza virus, which we’ll
get to in a second. A lot of people, use the terms Cold and flu interchangeably but they
are actually two different types of illnesses caused by two different types of viruses.
Colds are generally less serious and are usually limited to a runny nose, sore throat, and
cough. Flus, on the other hand, often involve additional symptoms such as a fever and muscle
pain all over your body. One virus that is closely related to the rhinovirus,
but far more serious, is the polio virus. The polio virus was a big problem in the 1950’s
but has since been almost eradicated, again, due to vaccination. Okay, now we’ve come to the one everyone
is talking about. The corona virus. The current corona virus, also called Covid-19, belongs
to Order Nidovirales and is closely related to the viruses that caused the earlier SARS
and MERS outbreaks. From what we know so far, the Covid-19 coronavirus is far more serious
than the influenza virus. It seems to spread more easily and seems to have a death rate
of at least 10 times that of the seasonal flu virus. More on what we can do during the
current outbreak in a moment. So previous viral outbreaks that you have
probably heard of include H1N1 and H5N1. Both of these are subtypes of the same virus that
causes the seasonal flu, a common Type 5 virus. In more recent years, H1N1 has been referred
to as swine flu but H1N1 it is actually the same type of virus that caused the major Spanish
Flu pandemic back in 1918. And this is probably a good time to point out the fact that some
viruses can in fact pass between animals and humans. So far, it seems that Covid-19 cannot
be transmitted via your dog or cat so don’t worry about that but do understand that viruses
are not something that effect humans only. Other type 5 viruses include Ebola, which
was a concern a few years back, as well as Measles and Mumps, two diseases that people
now get vaccinated for and are hence less of a concern than they once were. This leaves
us with Type 6 and 7 viruses, both of which are called “retroviruses”. I’ve only
listed one example here, the HIV virus, which is a type 6, and of course causes the disease
known as AIDS. Now, we often associate the word “retro”
with things that are old-fashioned. But “retro” simply means “backwards” and Type VI viruses
are called retroviruses because they replicate in a backwards manner.
Retroviruses are also special because they can actually insert themselves into the DNA
of living things. And when that DNA gets copied and passed on to the next generation, the
retroviruses are passed on too. It is estimated that about 5% of every human’s DNA is actually
retroviruses, most of which were inserted into our DNA millions of years ago. These
viruses no longer make us sick but serve as a record of our species’ genetic past. This actually ends up being one of lines of
evidence that can be used to support the theory of evolution. For example, if you compare
the DNA of a human with the DNA of a chimpanzee, you will find the same retroviruses in the
same locations, indicated that we share a common ancestor somewhere in the distant past. Okay, before we wind up, let me point out
that if there are any infectious diseases that we haven’t covered yet, it’s probably
because they are bacteria, not viruses. So, for example, the “bug” that caused the
Bubonic Plague, a.k.a. the Black Death, was not a virus. It was a bacteria – a single
celled living organism, as is Salmonella, E.Coli, Cholera, and a bunch of other so-called
“bad bacteria” that frequently cause human disease. And, in fact, it’s not just viruses and
bacteria that cause human infections. Malaria, for example, is a eukaryote cell, much larger
than a bacterial cell, and things like yeast infections and athlete’s foot are caused
by members of the fungus kingdom. But the thing that all of these infectious
agents have in common, whether they are viruses, bacteria, or fungus – is that they can be
passed from human to human. And how they are classified on this chart is no indication
of how serious they are. What we do know is that the current “bug” that we are worried
about – Covid19 is unfortunately, very serious. Not serious, as in, if you get it, you’re
definitely going to die but serious in that it spreads easily and therefore even if the
death rate is low, if we let it spread to millions of other humans, well, you do the
math. So, before I go, let me show you a few important
charts. First of all, from Google, here’s Do the Five. The one we’ve been hearing
a lot about is Hands. Wash them often. Soap literally kills the virus. So turn the tap
on. Wet your hands thoroughly with warm water. Then turn the tap off and soap them up good.
But here’s the important thing that most people forget – you have to get the whole
hand. This chart from an old nursing article shows the parts that tend to get missed. So
make sure you concentrate on them too. We then have Elbow. Cough into it. Coughing
is the number one way the virus is spread. When you cough without covering, you’re
spewing particles into the air that then land on surfaces or can be breathed in by other
people. Face. Don’t touch it. We touch lots of stuff all the time. Therefore, we could
have the virus on our hands. So until you can wash them, keep them away from your face
– because it’s through your ears, nose, and mouth, that that thing’s going to enter
you. Space. Keep a safe distance. Seriously, if
you don’t need to go out and come into contact with others, simply don’t. Watch YouTube
instead. And finally, feel sick? Stay home. Which brings me to this last chart by Toby
Morris. Basically, what you’re looking for is a fever and cough combined with difficulty
breathing. With the flu, it’s going to be a fever and cough combined more with body
aches and tiredness instead. And the cold’s totally different. If you just have a runny
nose and sore throat with no fever, it’s probably not Covid-19 Okay, stay say everyone. Thanks for watching.

64 thoughts on “How are Viruses Classified?

  1. Great job explaining all of these kinds of viruses. I learned something today (for once) even though those images kind of give me the heebie jeebies.

  2. I learned more in this video than I will on my crusty nasty online school.

    Also wow this is the smartest YouTube comment section lol. There are actually people who are being respectful and civil when making critiques and the creator responding respectfully to those suggestions.

  3. Hey Matt, Why don't you get into Taxonomy? I like the way you tell of classifications groupings categorisings.
    Birds, fish, places/origins of fruits vegs we eat, How about trees ?, Mushrooms ?

  4. but where are covid-1, covid-2, covid-3, covid-4, covid-5, covid-6, covid-7, covid-8, covid-9, covid-10, covid-11, covid-12, covid-13, covid-14, covid-15, covid-16, covid-17 and covid-18?

  5. If they need living things to survive and multiple, then they are parasites? Or they only have parasitic property. 😃

  6. 2:47 you don't need two bacteria to get a third bacteria either lol ! they self-replicate (asexually) like many other single-celled organisms

  7. Just one clarification: COVID-19 (Coronavirus disease 2019) is the disease, not the virus causing the disease. The virus is SARS-CoV-2 (Severe acute respiratory syndrome Coronavirus 2); the "2" is to distinguish it from SARS-CoV, the related virus which caused the SARS epidemic of 2003.
    So, just like HIV (Human immunodeficiency virus) can lead to AIDS, SARS-CoV-2 causes COVID-19.

  8. Can you make: A visual history of pandemics | World Economic Forum? How they're related one of the another or how the impact

  9. Small pox still exists within the USA's CDC virus storage labs, and both the Russian (known) and Chinese (assumed) equivalent government controlled labs.

  10. This video, like most Covid-19 videos, is demonetized (ad-free) and therefore won't be promoted as much by the YouTube algorithm. If you found it useful, please share via social media so that others can see it too. Liking and commenting helps too.

  11. i know how to categorize these viruses

    Coronavirus:
    COVID-19

    Not Coronavirus:
    Everything else

  12. I don’t believe in evolution. But there is an answer to this. If Viruses need a host, life would have had to evolved first right?

  13. COVID-19 is not a virus. It is a disease caused by the virus SARS-CoV-2. Please don't further the spread of misinformation regarding COVID-19 and SARS-CoV-2.

  14. @2m55s: "…The two initial [Non-living] viruses are just going to sit there until they DIE."
    Non-Living things can die? Semantics, yes I know. 🙂

  15. Can you possibly do the evolution of language so stay with the oldest language that are connected to the modern day language

  16. Thanks for the video. Good information and I have shared with others who may get confused between viruses and bacteria. 💖

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