BBC Learning English. I'm Neil.

And I'm Georgina.

Covid-19 has changed everyday life for

people in countries around the world.

But coronavirus

wasn't the first pandemic to cause mass

sickness and disrupt daily life.

Between 2002 and 2004 an outbreak

of the disease known as SARS

or 'severe acute respiratory

syndrome' caused hundreds of deaths

in southern China before

spreading to other parts of the world.

The virus that caused SARS survived

by mutating - changing as

it reproduced itself in the

bodies of infected people and this

caused the virus to create

strains - slight variations

of the original.

Covid-19, the disease caused by

the strain of the original SARS virus

we are experiencing

now, has been called SARS 2.

In this programme, we'll be looking at

the origins of Covid-19 and

hearing new evidence

about the scale of the threat we face

from the disease. And of course

we'll be learning

some new vocabulary as well. But first

it's time for our quiz question.

We know that white

blood cells make up part of the immune

system our body needs to fight

infectious diseases

like Covid-19. But how many white blood

cells per microlitre does the

average adult human

need? Is it: a) 7,000, b) 17,000,

or c) 70,000?

Hmmm, in that case I'd say more

is better, so c) 70,000.

OK, we'll find out the answer at the end

of the programme. Now, Georgina,

you mentioned

that the disease spreading across

the world today wasn't the first

Covid-19-type disease.

That's right. In fact a recent research

project in China has identified

over 700 different

types of coronavirus carried by bats.

Some of these virus strains

are thought to have

already crossed over to humans.

Dr Peter Daszak of New York's Eco-Health

Alliance thinks that new

strains of the virus have

the potential to cause future pandemics.

He spent years in the Chinese

countryside looking

for the coronaviruses that could

jump from bats to humans.

Here he is talking to the BBC World

Service programme, Science in Action...

It would have been great to have found

the precursor to SARS 2, but

what would have been

even better was to have found it before

SARS 2 emerged and raise

the red flag on it and

stop the outbreak. But we didn't do that.

What we were looking for were...

at the time

... our hypothesis was that SARS 1,

the original SARS virus which

we all thought had disappeared,

was still out there in bats ... and that

was what we were looking for.

So we found

a lot of SARS 1-related viruses.

Covid-19 may have been contained if

scientists had known more

about the disease's precursor

- that's a situation which existed before

something and led to the development of that

thing. Here, the precursor of Covid-19

was the original SARS 1.

Any new cases of the virus would

have been a red flag for another

outbreak - a symbol

of danger and that some action

needs to be taken.

Dr Daszak believed that some form of

SARS remained in bats and

based his investigations

on this hypothesis - an idea which is

suggested as a possible explanation

of something but

which has not yet been proved correct.

Another scientist working to prevent new

epidemics is the pathologist

Professor Mary Fowkes.

The original SARS was treated as a

respiratory disease which

attacks the lungs.

But when working with infected patients,

Professor Fowkes noticed that

Covid-19 was damaging

the brain, blood and other organs as well.

Clinicians have recognised that a lot of

patients that have Covid are

exhibiting confusion,

are not necessarily aware of their

environment appropriately,

some are having seizures, so

there are some central nervous system

abnormalities. And as you know,

a lot of patients are exhibiting

loss of sense of smell and that is a direct

connection to the brain as well.

In some infected patients coronavirus

attacks the central nervous

system - the body's main

system of nerve control consisting

of the brain and spinal cord.

When severe this can cause seizures -

sudden, violent attacks of an illness,

often affecting

the heart or brain.

It seems that Covid-19-type diseases are

not going to disappear any time soon.

Reminding us of the importance of the

scientific research we've

heard about today.

And the importance of boosting your

immunity - which reminds me

of today's quiz question.

You asked me how many white blood

cells per microlitre the human body has.

I said c) 70,000.

Well, if that's true you've definitely

boosted your immunity, Georgina,

because the correct

answer is c) 7,000.

Today we've been discussing the strains -

or slight variations, of the virus

which causes

Covid-19.

Covid-19 has a previous disease called

SARS as its precursor - a situation

which existed

before something and caused the

development of that thing.

Researchers used the idea that the virus

have passed to humans from

bats as their hypothesis

- possible explanation for something

which has not yet been proved true.

By identifying new virus strains, doctors

hope unexplained cases can act

as a red flag

- a warning sign of danger, to prevent

further outbreaks.

Knowing about new strains is increasingly

important as we find out more

about how coronavirus

attacks the body's central nervous system

- the brain and spinal cord, which in some

patients can cause seizures - sudden,

violent attacks of an illness,

especially affecting

the heart or brain.

So try to stay safe, wash your hands and

remember to join us again soon.

Bye for now!

Bye!