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’re going to start.
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 virus.
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 have evolved from viruses.
More recently, however, 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 know exactly how.
So for now, it’s best to just think of viruses as being something separate
because they do differ from everything else
in 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.
If you put a few bacteria 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 little 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 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 and Nobel Prize winner
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.
但是在这些数字之后 我们细分了目 科 属和物种
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 and more we can do
during the current outbreak in a moment.
So some other 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, or negative RNA 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.
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 Ⅵ and Ⅶ viruses,
both of which are called “retroviruses”.
I’ve only listed one example here, the HIV virus,
which is a type VI, 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 some sort of 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.
Interestingly, 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,
indicating 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,
比如 沙门氏菌 大肠杆菌 霍乱
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,
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
before you finally rinse all that soap off.
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 even without noticing.
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 the virus is going to enter you.
Space. Keep a safe distance.
Seriously, if you don’t need to go out and come into contact with others,
Watch YouTube instead.
And finally, FEEL sick? Stay home.
最后 感觉不舒服? 呆在家里
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.
基本上 你要找的是发烧 咳嗽和呼吸困难
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 safe everyone.
Thanks for watching.
Today I’m going to talk about viruses –