Viruses are one of the earliest forms of life as we know it.

They're little strings of genetic material (called RNA) coated in a protein jacket.

They've evolved to make people sick in very specific ways.

They hijack cells and use the cells to produce more viruses.

Once the virus is ready, can force its host to share it with others.

For example, the varicella-zoster virus (VZV) causes little red spots to appear all over

the infected person.

We call them chicken pox!

They are…

VERY.

ITCHY, and the virus did that on purpose!

It fills the pox with more viruses, so when people scratch them, they let the virus out

of their body, spreading it to people nearby.

It's actually pretty smart.

And this is how lots of viruses move through the population.

They get inside a body, and after a few days -- or, sometimes, years -- they'll try and

hitch a ride to another body.

The time from when they get inside a person to when they try and spread, is called the

incubation period.

During that time, the virus is invading cells, and fighting the immune system.

During the incubation period, if you have a virus, you might not even notice!

Chickenpox can take weeks before the first pox appear!

The flu, another common virus, is less patient.

Its incubation period is only half of a day.

It really wants to get out into the world again.

The flu spreads so fast through your friends because it can spread so fast in your body

too.

The influenza virus evolved to make you cough and sneeze, so it can hitch a ride on the

tiny droplets of water that come out when you do so!

Let's say Ian has the flu and coughs, then Autumn inhales a few droplets (even way later

in the day)...

Once inside her body, influenza virus hopes to hit an epithelial cell.

Epithelial cells line the airway and are the perfect place for a new flu virus to set up

shop.

Once it finds the right cell, it has to get inside, but cells don't just let anyone off

the street inside their membranes.

So, to convince the cell to let it in, viruses have little bumps on the outside of their

jacket -- called receptors.

Receptors are like keys, and if the virus has the right key, our cell will surround

it -- called endocytosis.

This can happen less than 10 minutes after a flu droplet is inhaled!

Once inside the cell, the influenza takes off its jacket -- it transforms.

From there, the little bit of genetic RNA material heads to nucleus of the cell, and

does something called "cap snatching."

It steals a "cap" from the host cell's RNA molecules and puts it on itself.

Once it's wearing the cap, the flu virus can trick the DNA in the nucleus to make more

flu virus -- again and again and again.

As more and more virus fills up the cytoplasm, the new guys steal bits of the cell's outer

membrane to put on a jacket and head out into the body.

Even though the influenza virus invades human cells really quickly, it can take a day or

two before you'll feel sick.

The immune system is on the prowl looking for infected cells and any virus in your bloodstream.

It's huge battle!

If you have a fever, or feel sore and achy, that's a side-effect of your immune system

attacking an infection.

Fevers change the body's temperature to try and slow the virus down.

The achyness comes from our own body try helping the immune cells trying to fight the infection.

After a few days, the immune system usually wins out, but chances are you've already spread

the virus to someone else.

Which means you've won the battle, but lost the war.

In the end, viruses aren't trying to hurt us, they're just fighting to survive.

They can be annoying, dangerous and even deadly, but learning about how they work has taught

us a lot about ourselves, and the history of life on our planet.

This video was written by our good friend Trace Dominguez.

He's got a YouTube channel where he looks at how the world works through the lens of

history and science.

Check out his latest series here where he explores the how the television business got

so big!

Make sure you come back every Monday for a brand new video.

As always, I'm Blocko and this has been Life Noggin.

Don't forget to keep on thinking!