Horizon (1964) s48e09 Episode Script
Why Do Viruses Kill?
In April 2009, the world was sent into panic by a mysterious agent.
One with the power to kill.
These are real people, real lives are being lost.
A disease was sweeping through populations, caused by an organism invisible to all but the most powerful instruments.
A virus.
The World Health Organisation says swine flu has now spread to nearly every country in the world.
For all our scientific advances, we still have a lot to learn.
We've no idea, basically, how viruses make a living, other than the fact that they have to infect something and replicate.
Why do viruses exist? We don't really know the answer to that question.
We don't even know how many there are.
There could be thousands of other viruses out there and we have no idea what they are, how they spread, what populations.
And because we struggle to understand them, they cause mass terror.
People must not panic.
But the carnage that was expected hasn't yet materialised.
'England's chief medical officer, Sir Liam Donaldson, 'says the swine flu pandemic is considerably less lethal than had been feared.
' Once more, we appear to have got the calculations wrong.
So when, and why do viruses kill? Here in Atlanta, Georgia, at the Centres for Disease Control and Prevention, teams of people are continually scanning the world for tell-tale signs.
Picking up clues from thousands of different sources, they're on the lookout for emerging diseases.
In April 2009, the alarm bells began to ring.
It happened on a Friday night.
I think I happened to be on call then.
I saw the e-mail traffic.
It was, at that point, routine.
Two children in San Diego, California, had come down with a new variant of flu.
The "new" wasn't that big a deal, because there were only two cases and the kids had already recovered.
The emergence of a new flu virus isn't that unusual.
The CDC regularly registers new outbreaks.
It's when particular patterns of infection emerge that they get concerned.
And this one stood out.
The big thing was, we knew something serious was going on in Mexico.
When the scientists said, "Those are the same virus that "we found in California," that's when people got excited.
The pattern of contagion convinced the CDC to set in motion a chain of events they'd been preparing for years.
from this getting as bad as it could.
Quarantines were ordered and emergency protocols were initiated to stem the outbreak.
We need to protect the vulnerable first.
They're more likely to be at risk of dying from this condition.
But it was already too late.
More cases of swine flu confirmed, this time in New Zealand and Israel.
Swine flu became the first global pandemic of the 21st century, sending a wave of panic across the world.
'The government closed all public places in a desperate attempt to stop the spread.
' 'Fear of the swine flu virus seems to be spreading at least as quickly as the disease.
' Of course I'm worried, I've got children.
'Health officials are watching this outbreak closely.
' As events spiralled, so, too, did rumour and fear.
Don't have the vaccine.
Tell as many people as you can, don't have the vaccine.
Want to know where swine flu came from? It came from Mexico.
What's next? What's next? What's next?! Predictions were made that up to 120 million people worldwide could be killed by the virus.
In the UK alone, the authorities were preparing for 65,000 deaths.
The reality so far has been altogether different.
The fatality rate for the swine flu virus in England has been published for the first time.
It shows the outbreak is less deadly than had been feared.
A study in the British Medical Journal suggested chances of dying, once infected, are around one in 4,000.
The nightmare scenario everyone feared hasn't materialised.
What this episode has taught us is how difficult it is to predict how viruses behave.
These tiny organisms continue to challenge even those that spend their careers studying them.
The virus is probably the smallest living organism.
If you think about the head of a pin, which is about one millimetre across Must have got one Isn't it amazing, in a lab, you can't find something simple like a pin? To give you an idea of how small viruses are, the rhinovirus that causes the common cold is about 20 nanometres in diameter.
If you lined up a whole load of rhinoviruses in a row, you'd need 50,000 of them to just cross the head of that pin.
They really are tiny.
Viruses come in all different shapes and sizes.
They can be just little round balls, they can have incredibly complex capsids that are made of proteins linked together with incredible symmetry.
And those are beautiful.
They're like looking at stained-glass windows.
They're wonderful, ordered structures.
Viruses may seem alien, but at their core, they're made of the same building blocks as ourselves - genes.
Think of it like a pill you're going to take, one of those capsulated pills with a little bit of stuff inside.
If you pulled the capsule apart, those little things that would fall out, that would be the genetic information inside the virus.
Kind of like an M&M.
It's got a chocolate shell on the outside, and genetic material on the inside.
Whilst viruses are made of the stuff of life, their existence questions what life is.
If you ask me whether the virus is alive or it's dead, my answer is yes.
Now, you may say, that's not an answer.
But I think it is, in fact.
A virus goes through a phase that's non-living.
It's floating around, and it's as dead as a ping-pong ball.
When the virus gets into a cell, it begins to have the attributes of something living.
While the virus is inside the cell, it can be looked at like a living entity.
It is once a virus infiltrates a cell that they reveal their potential, because this is where they reproduce.
They have to replicate inside a cell.
They can't just grow, if you give them growth medium like a bacterium could, for instance.
They have to find a particular cell that they can enter, and replicate in.
That particular place can be a plant cell, a microbe in the sea, or a cell in your nose.
The virus takes it over, forcing it to manufacture more virus particles.
It does this with tremendous efficiency.
You could imagine a virus being minute as compared to a human cell.
Yet this small virus particle will kill the cell, and reproduce 100,000 copies of itself within six hours.
When the cell has manufactured all it can, the virus can take a more devastating turn, causing the cell to explode, scattering millions of new virus particles.
It's a process studied in detail by Professor Geoffrey Smith.
Can you amplify that up a bit? Magnify it up? He stains virus particles green with a fluorescent colouring so he can see them in action.
So, the virus wants to spread from cell to cell.
What we're looking at here is the virus spreading from the top down to the bottom, across a lawn of cells that it can infect.
The green dots are individual virus particles and these larger aggregates of green, like this, are factories where new particles are being produced.
They're spreading down.
Here is a new cell that's just becoming infected.
A factory has now reproduced, new particles are being made, and those are then coming out and spreading to another cell further down.
This prodigious ability to replicate means there's no escaping viruses.
But the ones we fear are a tiny proportion of the total number of viruses on this planet.
To get a true understanding of the world of viruses, we need to examine their relationship with all life on Earth.
Professor Curtis Suttle is amongst those beginning to discover the diversity of viruses' existence.
In his half-litre of water, there are more viruses than there are people on the Earth.
We're probably looking at about 30 billion or so viruses in this half-litre of water.
Probably more than 100,000 different kinds of viruses.
And so It's about 22 parts per 1,000, sea water.
Completely harmless to humans.
That's why every time you swim, you'll swallow about 30 millilitres of sea water.
But it does you no harm at all.
Because these aren't viruses which infect us, these are viruses which infect the microbial life in the ocean, the plankton.
I'm letting them go, so they can live free.
Viruses are one of the dominant life-forms in the oceans.
It's not things like the fish that are driving the oceans, it's things like the viruses.
Those are the things that are really driving ocean ecosystems.
Viruses kill 20% of all the living material in the sea every day, releasing their contents for other organisms to use.
If there were no viruses in the ocean, things would just stop.
Things wouldn't grow.
There wouldn't be food for other organisms.
And they're not just in the sea.
Viruses can be found anywhere.
Viruses can survive vacuums, they can survive ultra cold, they can survive desiccation and they're so small that they aerosolise, so the air that we're breathing right now, that's going to be full of viruses coming off the ocean, because they're just suspended all the time.
They're so small, they're no different than water vapour, almost.
Viruses are the most abundant life-form on Earth.
If you laid all the viruses on the planet end to end, they would form a line 200 million light years long.
To understand why there are so many, we have to go back to the beginning of life on Earth.
Today, this is about as close as it gets to the conditions of the early Earth.
Yellowstone Park, Montana.
You go to weird places and you find weird things.
Yellowstone, if you ask most biologists, is a weird place.
Mark Young is Professor of Virology at Montana State University.
For him, going to Yellowstone Park is not just a field trip, it is a voyage back in time.
If you go back on this planet in the vicinity of 4 billion years ago, early Earth was a lot like what Yellowstone is today.
The organisms that we find in places like Yellowstone living in these kinds of environment are probably the cousins of some of the earliest life-forms on this planet.
Research undertaken here has led to an extraordinary new discovery that is shedding light on how long viruses have been on the Earth.
All life came from a last universal common ancestor, all life that we know about on the planet today.
We affectionately call that Luca.
That was the route from which all life stemmed at least 3.
5 billion years ago.
First came bacteria.
Then another branch called the eukaryotes evolved.
All the complex life-forms like fungi, plants, animals, including us.
In the 1970s, scientists discovered a third category of life that was entirely new to science.
They called it archaea, meaning the ancient ones.
The trick is not to lose the bottle in the hot springs.
It is a single-cell form of life that is really quite amazing.
We know in these hot springs if it is acidic and really hot, that there really isn't even any bacteria.
It is all archaea.
If you were using this as a hot tub, you would be poached alive very quickly, but if you are an archaea, you HAVE to live in these environments.
Many scientists believe archaea are the earliest form of life, older even than bacteria.
But Professor Young was looking for something else.
To our surprise, no one had ever come to look for the viruses that live and replicate in these hot springs.
He uncovered something remarkable.
The archaea were riddled with viruses.
It has been a rock'n'roll ride looking at these new viruses because they are completely different to any viruses we have ever seen before on this planet.
An ancient life form with ancient viruses, this discovery convinced Professor Young that viruses are much older than we previously thought.
What we think now is that viruses certainly are ancient, that they were here when life was first evolving.
Some of us even push it further and speculate that viruses actually preceded cellular life as we know it today.
Viruses have been infecting life from the moment it first emerged.
They're a huge evolutionary driving force.
They have helped determine what has lived and what has died.
Viruses play such a critical role in the evolution of life, it is hard to imagine that life could have evolved on this planet without viruses.
As complex life-forms like plants and animals began to evolve, the viruses found their way into them too.
Over millennia, viruses have come to dominate the world, infiltrating every type of living thing.
To do so they had to find a way to do the one thing a simple packet of genes can't do alone.
Move.
This cage here contains probably one of the most notorious virus vector species in the world.
It is a whitefly species called bemisia tabaci.
The common name is the tobacco whitefly or cotton whitefly.
As neither viruses nor plants can move by themselves, viruses evolve to infect those species which can.
This whitefly is completely oblivious to the fact that it is carrying around a dangerous cargo .
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up to 100 different plant viruses.
This insect which is less than a millimetre in length is actually responsible for phenomenal crop damage around the world.
Wanting to make the most of their transport, the viruses get into the whitefly's stomach but don't harm the fly.
The virus travels with the fly to the next plant and then, as the fly feeds, it unknowingly injects the virus into the plant.
At the same time the insect's feeding and putting the virus into the new plant, it is also laying eggs, so you end up with a small population of the insect developing on there.
Which, when it goes through its life stages and emerges as a new white fly, it will have the virus in it and pass that on to another plant.
It continues the cycle that way.
This is one of myriad methods that viruses use to spread.
They can co-opt our most basic actions.
Viruses like hepatitis B use our need to reproduce to pass themselves on.
Other viruses have even evolved to manipulate our very behaviour to their own ends.
The rabies virus gets into the brains of those it infects, making them aggressive, actually encouraging them to bite and pass it on.
The flu virus has an equally ingenious transmission mechanism, one that is highly efficient and practically unavoidable.
If we believe the idea that coughs and sneezes spread diseases, then of course when you are infected with the respiratory virus it attacks that very part of your nose and then induces you to sneeze.
It has engineered a way to jump out from one host to another which, for a tiny virus, is quite a big barrier to overcome.
Flu forces you to unwittingly pass it on.
Today it uses a slightly less natural means of transport.
Their only needs to be one person in this group here with flu.
Get on the bus, be coughing, on their hands, put it on the bus rail, I come along and touch it and I have got myself infected.
The cold weather is coming on.
This temperature makes the virus more stable.
It will hang around for much longer, there is no bright sunlight to destroy it, no high temperatures, all nice and cool.
This is flu's moment and it will take it.
Being able to transmit easily is what makes the influenza virus so dangerous.
The textbook viruses, like Ebola, and Lassa, students love them because they cause horrible diseases and they kill 50% of people they infect.
But they're not very infectious.
But other viruses that people might view as less threatening and, mistakenly, a lot of people view influenza as like a common cold virus, but they are mistaken.
Because that is the single virus that can take off from any spot in the world.
You've seen it take off from Mexico.
It can take off from any spot in the world, circumnavigate the world in a matter of months and cause untold devastation.
Viruses can transmit so effectively that they have infiltrated every living species in the world, and we are no exception.
I think it is remarkable, each person walking by has a plethora of viruses in them.
They have at least four viruses, everyone, me included.
We will have an enterovirus, a chicken pox virus, a herpes virus, a wart virus as well.
Throughout our lives, we suffer a continuous onslaught.
Over a lifetime, one would be attacked by probably 500, 600, 1,000 different viruses of all kinds of families.
Each of these has a different way to attack its host.
HIV appears to be particularly cunning.
HIV is the king of clever viruses.
It replicates in the kinds of cells that are designed to detect and destroy incoming viruses in the human body.
So, it's perfect.
Others go for different parts of our bodies.
Some viruses are transmitted sexually and they cause lesions in that area of the body.
Other viruses spread around the whole body, like smallpox.
Fair enough, the virus is exemplified by all the pox, but really, that's not killing you.
What is killing you is the virus replicating in your internal organs.
The most deadly virus of all hides in dogs, rodents and bats.
Rabies is probably the only virus that I know that can cause death in 100% of victims.
The reason for that is, of course, it invades the central nervous system.
It might take a long time to do it.
It will depend where you were bitten.
If you're bitten on your arm, it will take quite a long time for that virus to move up the nerve system to the brain, but in the end it will.
It might take two months or three months, but in the end, rabies will get to your central nervous system, replicate, destroy cells in the central nervous system and that will give you the symptoms of hydrophobia, dizziness, all the symptoms that will in the end kill you.
Respiratory viruses like SARS or influenza replicate in the airways and air sacs of our lungs causing an immune reaction.
It's when this response escalates that it causes problems.
These are people that, for some reason or another, have not managed to contain the virus well in the nose and throat, which is where the virus entered their body, and the virus has then managed to penetrate deeper into the lung.
There it's destroying cells of the lung that are important in helping the lung work and it's also of course triggering an immune response to itself, which is clogging up the lungs and stopping the lungs from doing their job as well.
And the people are dying of pneumonia.
Every virus has its own little way of digging in.
Every virus has its own little way of replicating and you have your way of responding.
The combination sometimes is overwhelming.
Although viruses infect each and every one of us, somehow life continues.
That's because if a virus has been around for a while, our immune systems have a chance to adapt and build up protection.
The viruses that do most damage are the ones that are new to us.
But these don't come along very often, for the simple fact that most viruses don't belong in humans.
A lot of human viruses and particularly the most important ones - hepatitis B, for example, HIV, influenza - they came from the animal or bird reservoirs on this planet.
I think in influenza, it's not basically a human virus.
It can be humanised, but basically at heart it's a bird virus.
At heart it loves to be in a great migrating swan, in a duck, in a goose.
It doesn't really want to be in humans, I think.
Avian flu can be mild in a bird, but fatal in a human.
But for a virus to move from infecting an animal to infecting a person, it has to overcome a massive barrier.
The biggest hurdle they have is what's called the lock and key problem.
That is, it's got to latch on to a human cell.
I mean, with influenza for example, I mean, here's an influenza virus, it's got its little latch here on this protein here.
Right at the tip of this protein.
Because if this virus is living in a migrating bird for example, the little tip here is always adjusted so that the virus can infect bird viruses, other birds.
And that small protein tip is what stops the virus from infecting us.
Most of the time.
It has a big difficulty, because it won't fit onto a human cell.
And so it has to mutate along the tip here.
And by chance, you'll have a mutation here.
A change at the tip which enables one particular virus, on one particular day, in one particular place to latch on to a human cell in a human.
From that chance event, viruses can jump the species barrier and get a foothold in human populations.
Nowhere is this more vividly experienced than here - the Democratic Republic of Congo.
This region of jungle is the front line of our battle with viruses.
Some of the most dangerous diseases in history have jumped into humans from these rainforests of central Africa.
In the last 20 years, there've been a number of viruses that have been discovered in these areas, including Ebola and monkey pox.
HIV has also come from this area.
So, there could be thousands of other viruses out there and we have no idea what they are, how they spread and what populations.
Epidemiologist Dr Anne Rimoin is in search of the next disease threatening to cross species.
It's called monkey pox.
Well, monkey pox is a disease, it's a cousin of smallpox.
It's found in animals, originally, and not in humans.
What makes this area so fertile for fatal human viruses is that humans here interact so closely with wild animals.
Monkey pox is found in a lot of the local monkeys and squirrels and some of the rodents that people eat on a day-to-day basis here.
GUNSHO It's this close contact between monkeys and humans which gives the virus opportunities to spread.
ALL CHAT IN FRENCH They're very, very forcefully, they were saying yes, indeed.
They eat it every single day.
And, in fact, if they don't eat it, they lose power.
They're less forceful.
They're less able to work.
So, we're saying you have to be very, very careful with these monkeys because you can see that there are, these teeth are very, very sharp.
And so you can see it's a very easy way for viruses to spread between humans and animals.
People are cutting these animals, there's blood everywhere, they're getting bitten and scratched by these animals.
This is just a very typical scenario of how viruses can cross species between animals and humans.
Monkey pox is a devastating disease that kills up to 10% of people it infects.
We're looking for pock marks.
You can see some pock marks here, here He has another scar right here as well.
Here, here Cases of human-to-human transmission have occasionally been recorded.
But at the moment, it's mainly those who have direct contact with infected animals who contract it.
They found dead squirrels, brought them home, they ate them and they all ended up getting monkey pox.
So, they didn't get monkey pox from each other.
They got it all from the same source at the same time.
It can be passed from one person to another.
There have been documented up to eight serial transmissions, meaning that up to There have been up to eight generations of monkey pox passed from one person and then onto the next person, on to the next person, on to the next person.
It's because the monkey pox virus is only limitedly contagious between people that it's currently contained here in central Africa.
But if it does evolve to pass freely from human to human, the way we live today makes its spread inevitable.
As people and populations become more urbanised, viruses will more easily find themselves into urban centres, like here in Kinshasa, and then, through international travel, be spread throughout the world.
Our first lines of defence remain intelligence of emerging diseases and containment when we find them.
There's no way to prevent viruses from emerging.
New viruses emerge all the time.
The question is, are we aware of them or are we not? So, the only way we're going to know is if we have good disease surveillance.
For example, if we had known about HIV early on, we would have been able to do more to prevent the spread of HIV in populations.
Here in Congo, for example, the first case of HIV that was reported was in 1958.
Now, that's based on recent analysis.
It wasn't in 1958, we didn't know But if in 1958 we had known that HIV was lurking in populations, we might have been able to do more to be able to prevent what's happened and having it become a worldwide pandemic.
But we're not totally defenceless.
For some viruses, we have vaccines.
It's quite possible that this man has saved more lives than anyone else alive today.
His team fought a battle against one of the deadliest diseases we've ever encountered - smallpox.
Oh my God.
Oh my God.
What a life.
Disgusting.
Awful.
Ugh.
No.
Oh my God.
This little girl, my goodness.
Look at these lesions here.
They're just almost all bumping against each other.
The mother holding a baby again with a quite extensive rash.
The baby has a face that's swollen.
He's got a lot of pustules there.
He looks miserable enough.
And in a young child like this, I think the probability of death is fairly high.
The smallpox virus kills about one in every three people who catch it.
Smallpox, throughout history, has been the world's worst pestilential disease.
And it was greatly feared everywhere.
There are approximately 10 million cases a year and about 2 million deaths.
Not only deadly, but also highly infectious.
Smallpox is transmitted from person to person really with droplets.
An individual with the disease and the rash has the rash inside the mouth and little pustules.
He speaks and the droplets are expelled and there's a smallpox virus, so you inhale the virus and that's the way you get the disease.
Just by talking to somebody.
Yet smallpox is one of the few viruses for which we have a vaccine.
Using an agent that resembles the virus, the vaccine stimulates the body's immune system to recognise the real virus in future, protecting you from infection.
And there is one other feature of the smallpox virus that makes it vulnerable.
It's been circulating in humans for so long, it's lost the ability to infect other animals.
It's only possible host is us.
Back in 1967, the World Health Organisation realised this presented a strategic opportunity.
If they could vaccinate enough people, they would leave smallpox nowhere to go.
Nowhere to hide.
So a WHO team, headed by DA Henderson, hunted down outbreaks of smallpox and vaccinated everyone who might be at risk.
Considering the 10 million infections per year, it was a daunting task.
But just a decade later, smallpox was completely eradicated from the community.
We felt we had finally won a real battle.
We'd outwitted the virus and eventually removed it from the face of the Earth.
The eradication of the smallpox has got to be one of the great achievements of mankind.
The co-ordination that a vaccination campaign like that takes is just incredible.
In the 20th century, 300 million people died of smallpox.
It's the only human disease that has been eradicated and one cannot really estimate the value of this to mankind.
The smallpox virus presented a unique set of biological circumstances that meant it could be eradicated.
Other viruses have abilities that smallpox doesn't.
They can change their structure, so they're always one step ahead of a vaccine.
They can mutate.
And one virus does this with incredible efficiency.
About twenty years ago, I felt fine about life.
I felt good about life.
My partner and I were expecting a baby in '92, and I was full of excitement about that.
I think he was feeling a bit terrified! In 1992, Alice Welbourne already had two children.
Her GP recommended several routine antenatal tests.
She phoned me up, I guess a week or so later, and I could just tell by the tone of her voice that something serious was up.
And I went in and I sat down, and I can still remember the Venetian blinds, you know, those horrid grey metal Venetian blinds, across the window.
And she just said, "It's HIV.
Everything else is fine.
"It's the HIV.
" It was just completely devastating, because I was completely fit and well.
I had no realisation at all that I might have anything the matter with me and instantly thought, "OK, well, I'm obviously just going to have to prepare for my death.
" HIV is able to pass under our immune radar.
Thousands of virus particles can infect human cells, initially without a person even being aware.
They then quietly multiply, undisturbed, in Alice's case threatening both her and her unborn baby.
We made the decision that we were just going to have to go ahead with a medical termination, and that's one of the toughest decisions I've ever had to make in my life.
HIV has a particular strategy that's meant it's beaten our attempts to produce a vaccine.
HIV mutates at an alarming rate.
As it copies itself, it's continuously changing.
One of the reasons that vaccine development against HIV is so difficult is that, like influenza virus, it can change and makes mistakes, it's sloppy.
You might think that's a bad thing, but actually it's not.
If you're a virus, it's very good.
The genes of HIV can be represented as a series of letters.
Once the virus gets into us, it copies itself.
But because it's constantly making mistakes, some of the offspring will be different .
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presenting our immune system with an enemy that is never quite the same.
So it's a very quick and dirty strategy that viruses like to use in order to be able to change rapidly in response to things we throw at them, like drugs and vaccines.
So that if we did make a vaccine against one particular strain of HIV, there would be so many others appearing rapidly that the vaccine really would not be effective.
There is now a successful treatment for HIV, using antiretroviral drugs, but these, too, have to overcome HIV's ability to mutate.
Whilst single antiretroviral drugs don't work for long before the virus acquires resistance, a combination of three different drugs at the same time can overcome this.
For Alice, the nine years of taking them has had a remarkable effect.
I've probably got as good a life expectancy here in the UK as anybody else of my age.
But it's a constant battle.
The virus can still mutate and become resistant to these drugs.
You know, we have so much science, we have so much technology, the assumption is there that surely we ought to be able to control viruses.
But of course, what having HIV has brought home to me is how unreal that illusion is, and how we are all living on the edge.
HIV's ability to endlessly mutate and evade our immune system has so far caused the death of over 25 million people.
Today, more than 35 million people worldwide live with the virus.
An ability to mutate is what defines some of the most successful viruses, including H1N1.
Against an individual virus, you can clearly make a vaccine, and we know how to do that, and we are making a vaccine at the moment for H1N1.
But then the virus will change, and next year we'll have a slightly different virus, or some time in the future we may have a radically different virus.
So we're always having to make new vaccines to combat the new strain that arises.
Alongside mutation, influenza exploits another ability of viruses.
We can be infected by more than one virus at a time.
And if these viruses meet, they can swap their genes around, giving birth to totally new viruses.
This process is called re-assortment.
It's formed by two swine viruses co-infecting the same cell, shuffling their pack of genes, and a new variant coming out that has got genes derived from both parents.
That's what I like to call "viral sex", because it's like two parents mixing their genes up together and making a new type of progeny.
In the case of H1N1, swine flu, it was a multiple re-assortment.
What we can sum up with swine flu is that it's got two genes that were very recently in a bird virus, it's got one gene that was very recently in a human virus, and then the remaining genes were recently in pig viruses, but in two different pig viruses that were in two different continents.
In an instant, this re-assortment created a new virus that was able to infect humans, one that was shockingly new to our immune systems and highly infectious.
This could be the first flu pandemic for over forty years.
Swine flu went from a few isolated incidents in Mexico in mid-April 2009 '.
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advising caution when travelling to the affected areas.
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to a worldwide pandemic in just two months.
The first case of swine flu in Europe has been confirmed in Spain.
Swine flu has now spread across at least five countries.
The Health Protection Agency says as many as seven hundred potential cases are being investigated.
The World Health Organisation says swine flu has now spread to nearly every country in the world.
But whilst highly infectious, it wasn't as dangerous as feared.
For all our modelling, we were still unable to predict the effect of the pandemic with any accuracy.
'The swine flu pandemic is considerably less lethal 'than had been feared.
' But maybe that shouldn't have come as much of a surprise, because the one thing viruses don't want to do is kill us.
I think viruses don't really want to kill us, if you see what I mean.
It's not much advantage to them if they're replicating in us and suddenly we fall over the table.
You know? They can't transmit onto someone else.
Every virus has to strike a fine evolutionary balance between being able to replicate successfully and multiplying so much it destroys its host.
In reality, when you go and look in nature, you actually see that many viruses don't kill their hosts.
They've evolved with their hosts so that they're living in a wonderful symbiosis of being able to still replicate without destroying their host, because it really doesn't make any sense to kill the home that you need to make more of yourself.
You know, even the viruses beloved of medical students like Ebola, Lassa, they're not huge killers.
They're not killing 80% of people or anything like that.
So it's a very exceptional virus that kills more than about ten per cent, and most viruses kill many, many, many fewer than that.
The most successful viruses infect millions but kill few.
On that basis, swine flu, with its high levels of contagion but relatively low death rate, is, arguably, successful.
But that's not to say there may not one day be a flu virus that can kill millions.
The current viruses can mutate and give new strains, but also there's a fantastic opportunity for new strains to come along that we don't have immunity to.
The question is, what's going to be the next pandemic? Already we're thinking about the next one.
For that day, we need to be ready, and one man is doing all he can.
Professor Eckard Wimmer had an incredibly simple idea.
He believed if he were able to build a virus from scratch, we would learn so much about how they work it would open new opportunities to create vaccines or even cures.
But to achieve this would mean attempting something highly controversial that had never been done before.
Professor Wimmer would need to recreate life itself.
That's what I was called.
I was Frankenstein in one of the papers.
Except they said I was Little Frankenstein, and I was insulted.
In 2002, Eckard Wimmer realised viruses are simply strings of chemicals.
This is the formula for the polio virus.
He wondered whether they could mix a set of these chemicals together and recreate the living, reproducing polio virus just from its basic ingredients.
We were nervous about that.
You're doing an experiment nobody else had done, and so there's always a possibility of a surprise.
Like all viruses, polio is simply a collection of genes protected by a shell.
In the case of polio, this genetic material is made of chemicals similar to DNA, called RNA.
It's this long string of genetic material that Wimmer was trying to make.
The problem was, they needed 7,500 pieces of RNA in an exact sequence.
So, what do you do? You cut up the 7,500 nucleotides on the computer, actually, you do it on the computer.
You cut them up into smaller pieces.
In fact, you mail order them.
All Professor Wimmer had to do was call up a commercial laboratory, order his gene fragments, and wait for the post.
From these fragments, they had to assemble the complete genome of the polio virus piece by piece.
Whilst complex, this stage was nothing new.
It was the next part that was controversial.
They had to make this collection of genes live.
And now we had this RNA, and we had to kick the RNA into behaving like a biological entity.
As you say in the computer language, we had to boot life into this biological program.
We took this RNA, and mixed it with a cell-free juice.
That juice was produced from human cells which we opened up.
We threw away the nuclei and mitochondria which are large organelles, and were left with an almost clear juice still containing lots of goodies that the cell has in the cytoplasm.
And now we took the RNA and mixed that with that juice.
Lo and behold, the RNA woke up.
This was really remarkable.
The mail-order collection of RNA, simple chains of chemicals, started building more copies of themselves and then new shells, and then these component parts assembled themselves into new virus particles.
We had synthesised a virus particle outside living cells, thereby violating the dogma that viruses absolutely need a living cell environment in order to replicate.
These home-made viruses were identical to the natural viruses.
Eckard Wimmer had re-created life and opened the doors to whole new areas of learning.
In terms of what Eckard Wimmer was the first to do, which was to create a virus from a piece of synthetic DNA, that has already massively changed what we can study in terms of viruses and, therefore, our ability to ultimately combat them.
The ability to tailor-make vaccines to new viruses as they arrive, the ability to understand, at every detail, which bits of the virus make it more or less pathogenic and be precise about it, because of what Eckard Wimmer did, it has revolutionised the field.
It is a huge breakthrough.
Discoveries like this have brought us as close as we have ever been to understanding and controlling viruses.
But constraining viruses completely, if even possible, is an impulse we should resist.
Viruses actually have been very important in the development of you and me.
So on the one hand, we still have the enemy.
On the other hand, we know viruses have been good for us.
It's a sentiment shared by many.
Our lives and viruses are intertwined.
They are a major and important component of all ecosystems of this planet and I don't think anyone could imagine how life could have evolved, or could even operate today without the presence of viruses.
And all life includes us.
We don't know, actually, how much we are dependent on the viruses that infect us.
Or replicate in us.
We think of them as pathogens, but actually, we very, very likely are highly co-evolved together.
Our immune defences have been shaped by the threat of viruses.
But, equally, the threat of our defences make the viruses evolve.
Science is beginning to reassess our relationship with viruses and their role in shaping life on Earth.
And I like to think that we're actually here to support the replication of viruses and everyone's been thinking of this backwards.
One with the power to kill.
These are real people, real lives are being lost.
A disease was sweeping through populations, caused by an organism invisible to all but the most powerful instruments.
A virus.
The World Health Organisation says swine flu has now spread to nearly every country in the world.
For all our scientific advances, we still have a lot to learn.
We've no idea, basically, how viruses make a living, other than the fact that they have to infect something and replicate.
Why do viruses exist? We don't really know the answer to that question.
We don't even know how many there are.
There could be thousands of other viruses out there and we have no idea what they are, how they spread, what populations.
And because we struggle to understand them, they cause mass terror.
People must not panic.
But the carnage that was expected hasn't yet materialised.
'England's chief medical officer, Sir Liam Donaldson, 'says the swine flu pandemic is considerably less lethal than had been feared.
' Once more, we appear to have got the calculations wrong.
So when, and why do viruses kill? Here in Atlanta, Georgia, at the Centres for Disease Control and Prevention, teams of people are continually scanning the world for tell-tale signs.
Picking up clues from thousands of different sources, they're on the lookout for emerging diseases.
In April 2009, the alarm bells began to ring.
It happened on a Friday night.
I think I happened to be on call then.
I saw the e-mail traffic.
It was, at that point, routine.
Two children in San Diego, California, had come down with a new variant of flu.
The "new" wasn't that big a deal, because there were only two cases and the kids had already recovered.
The emergence of a new flu virus isn't that unusual.
The CDC regularly registers new outbreaks.
It's when particular patterns of infection emerge that they get concerned.
And this one stood out.
The big thing was, we knew something serious was going on in Mexico.
When the scientists said, "Those are the same virus that "we found in California," that's when people got excited.
The pattern of contagion convinced the CDC to set in motion a chain of events they'd been preparing for years.
from this getting as bad as it could.
Quarantines were ordered and emergency protocols were initiated to stem the outbreak.
We need to protect the vulnerable first.
They're more likely to be at risk of dying from this condition.
But it was already too late.
More cases of swine flu confirmed, this time in New Zealand and Israel.
Swine flu became the first global pandemic of the 21st century, sending a wave of panic across the world.
'The government closed all public places in a desperate attempt to stop the spread.
' 'Fear of the swine flu virus seems to be spreading at least as quickly as the disease.
' Of course I'm worried, I've got children.
'Health officials are watching this outbreak closely.
' As events spiralled, so, too, did rumour and fear.
Don't have the vaccine.
Tell as many people as you can, don't have the vaccine.
Want to know where swine flu came from? It came from Mexico.
What's next? What's next? What's next?! Predictions were made that up to 120 million people worldwide could be killed by the virus.
In the UK alone, the authorities were preparing for 65,000 deaths.
The reality so far has been altogether different.
The fatality rate for the swine flu virus in England has been published for the first time.
It shows the outbreak is less deadly than had been feared.
A study in the British Medical Journal suggested chances of dying, once infected, are around one in 4,000.
The nightmare scenario everyone feared hasn't materialised.
What this episode has taught us is how difficult it is to predict how viruses behave.
These tiny organisms continue to challenge even those that spend their careers studying them.
The virus is probably the smallest living organism.
If you think about the head of a pin, which is about one millimetre across Must have got one Isn't it amazing, in a lab, you can't find something simple like a pin? To give you an idea of how small viruses are, the rhinovirus that causes the common cold is about 20 nanometres in diameter.
If you lined up a whole load of rhinoviruses in a row, you'd need 50,000 of them to just cross the head of that pin.
They really are tiny.
Viruses come in all different shapes and sizes.
They can be just little round balls, they can have incredibly complex capsids that are made of proteins linked together with incredible symmetry.
And those are beautiful.
They're like looking at stained-glass windows.
They're wonderful, ordered structures.
Viruses may seem alien, but at their core, they're made of the same building blocks as ourselves - genes.
Think of it like a pill you're going to take, one of those capsulated pills with a little bit of stuff inside.
If you pulled the capsule apart, those little things that would fall out, that would be the genetic information inside the virus.
Kind of like an M&M.
It's got a chocolate shell on the outside, and genetic material on the inside.
Whilst viruses are made of the stuff of life, their existence questions what life is.
If you ask me whether the virus is alive or it's dead, my answer is yes.
Now, you may say, that's not an answer.
But I think it is, in fact.
A virus goes through a phase that's non-living.
It's floating around, and it's as dead as a ping-pong ball.
When the virus gets into a cell, it begins to have the attributes of something living.
While the virus is inside the cell, it can be looked at like a living entity.
It is once a virus infiltrates a cell that they reveal their potential, because this is where they reproduce.
They have to replicate inside a cell.
They can't just grow, if you give them growth medium like a bacterium could, for instance.
They have to find a particular cell that they can enter, and replicate in.
That particular place can be a plant cell, a microbe in the sea, or a cell in your nose.
The virus takes it over, forcing it to manufacture more virus particles.
It does this with tremendous efficiency.
You could imagine a virus being minute as compared to a human cell.
Yet this small virus particle will kill the cell, and reproduce 100,000 copies of itself within six hours.
When the cell has manufactured all it can, the virus can take a more devastating turn, causing the cell to explode, scattering millions of new virus particles.
It's a process studied in detail by Professor Geoffrey Smith.
Can you amplify that up a bit? Magnify it up? He stains virus particles green with a fluorescent colouring so he can see them in action.
So, the virus wants to spread from cell to cell.
What we're looking at here is the virus spreading from the top down to the bottom, across a lawn of cells that it can infect.
The green dots are individual virus particles and these larger aggregates of green, like this, are factories where new particles are being produced.
They're spreading down.
Here is a new cell that's just becoming infected.
A factory has now reproduced, new particles are being made, and those are then coming out and spreading to another cell further down.
This prodigious ability to replicate means there's no escaping viruses.
But the ones we fear are a tiny proportion of the total number of viruses on this planet.
To get a true understanding of the world of viruses, we need to examine their relationship with all life on Earth.
Professor Curtis Suttle is amongst those beginning to discover the diversity of viruses' existence.
In his half-litre of water, there are more viruses than there are people on the Earth.
We're probably looking at about 30 billion or so viruses in this half-litre of water.
Probably more than 100,000 different kinds of viruses.
And so It's about 22 parts per 1,000, sea water.
Completely harmless to humans.
That's why every time you swim, you'll swallow about 30 millilitres of sea water.
But it does you no harm at all.
Because these aren't viruses which infect us, these are viruses which infect the microbial life in the ocean, the plankton.
I'm letting them go, so they can live free.
Viruses are one of the dominant life-forms in the oceans.
It's not things like the fish that are driving the oceans, it's things like the viruses.
Those are the things that are really driving ocean ecosystems.
Viruses kill 20% of all the living material in the sea every day, releasing their contents for other organisms to use.
If there were no viruses in the ocean, things would just stop.
Things wouldn't grow.
There wouldn't be food for other organisms.
And they're not just in the sea.
Viruses can be found anywhere.
Viruses can survive vacuums, they can survive ultra cold, they can survive desiccation and they're so small that they aerosolise, so the air that we're breathing right now, that's going to be full of viruses coming off the ocean, because they're just suspended all the time.
They're so small, they're no different than water vapour, almost.
Viruses are the most abundant life-form on Earth.
If you laid all the viruses on the planet end to end, they would form a line 200 million light years long.
To understand why there are so many, we have to go back to the beginning of life on Earth.
Today, this is about as close as it gets to the conditions of the early Earth.
Yellowstone Park, Montana.
You go to weird places and you find weird things.
Yellowstone, if you ask most biologists, is a weird place.
Mark Young is Professor of Virology at Montana State University.
For him, going to Yellowstone Park is not just a field trip, it is a voyage back in time.
If you go back on this planet in the vicinity of 4 billion years ago, early Earth was a lot like what Yellowstone is today.
The organisms that we find in places like Yellowstone living in these kinds of environment are probably the cousins of some of the earliest life-forms on this planet.
Research undertaken here has led to an extraordinary new discovery that is shedding light on how long viruses have been on the Earth.
All life came from a last universal common ancestor, all life that we know about on the planet today.
We affectionately call that Luca.
That was the route from which all life stemmed at least 3.
5 billion years ago.
First came bacteria.
Then another branch called the eukaryotes evolved.
All the complex life-forms like fungi, plants, animals, including us.
In the 1970s, scientists discovered a third category of life that was entirely new to science.
They called it archaea, meaning the ancient ones.
The trick is not to lose the bottle in the hot springs.
It is a single-cell form of life that is really quite amazing.
We know in these hot springs if it is acidic and really hot, that there really isn't even any bacteria.
It is all archaea.
If you were using this as a hot tub, you would be poached alive very quickly, but if you are an archaea, you HAVE to live in these environments.
Many scientists believe archaea are the earliest form of life, older even than bacteria.
But Professor Young was looking for something else.
To our surprise, no one had ever come to look for the viruses that live and replicate in these hot springs.
He uncovered something remarkable.
The archaea were riddled with viruses.
It has been a rock'n'roll ride looking at these new viruses because they are completely different to any viruses we have ever seen before on this planet.
An ancient life form with ancient viruses, this discovery convinced Professor Young that viruses are much older than we previously thought.
What we think now is that viruses certainly are ancient, that they were here when life was first evolving.
Some of us even push it further and speculate that viruses actually preceded cellular life as we know it today.
Viruses have been infecting life from the moment it first emerged.
They're a huge evolutionary driving force.
They have helped determine what has lived and what has died.
Viruses play such a critical role in the evolution of life, it is hard to imagine that life could have evolved on this planet without viruses.
As complex life-forms like plants and animals began to evolve, the viruses found their way into them too.
Over millennia, viruses have come to dominate the world, infiltrating every type of living thing.
To do so they had to find a way to do the one thing a simple packet of genes can't do alone.
Move.
This cage here contains probably one of the most notorious virus vector species in the world.
It is a whitefly species called bemisia tabaci.
The common name is the tobacco whitefly or cotton whitefly.
As neither viruses nor plants can move by themselves, viruses evolve to infect those species which can.
This whitefly is completely oblivious to the fact that it is carrying around a dangerous cargo .
.
up to 100 different plant viruses.
This insect which is less than a millimetre in length is actually responsible for phenomenal crop damage around the world.
Wanting to make the most of their transport, the viruses get into the whitefly's stomach but don't harm the fly.
The virus travels with the fly to the next plant and then, as the fly feeds, it unknowingly injects the virus into the plant.
At the same time the insect's feeding and putting the virus into the new plant, it is also laying eggs, so you end up with a small population of the insect developing on there.
Which, when it goes through its life stages and emerges as a new white fly, it will have the virus in it and pass that on to another plant.
It continues the cycle that way.
This is one of myriad methods that viruses use to spread.
They can co-opt our most basic actions.
Viruses like hepatitis B use our need to reproduce to pass themselves on.
Other viruses have even evolved to manipulate our very behaviour to their own ends.
The rabies virus gets into the brains of those it infects, making them aggressive, actually encouraging them to bite and pass it on.
The flu virus has an equally ingenious transmission mechanism, one that is highly efficient and practically unavoidable.
If we believe the idea that coughs and sneezes spread diseases, then of course when you are infected with the respiratory virus it attacks that very part of your nose and then induces you to sneeze.
It has engineered a way to jump out from one host to another which, for a tiny virus, is quite a big barrier to overcome.
Flu forces you to unwittingly pass it on.
Today it uses a slightly less natural means of transport.
Their only needs to be one person in this group here with flu.
Get on the bus, be coughing, on their hands, put it on the bus rail, I come along and touch it and I have got myself infected.
The cold weather is coming on.
This temperature makes the virus more stable.
It will hang around for much longer, there is no bright sunlight to destroy it, no high temperatures, all nice and cool.
This is flu's moment and it will take it.
Being able to transmit easily is what makes the influenza virus so dangerous.
The textbook viruses, like Ebola, and Lassa, students love them because they cause horrible diseases and they kill 50% of people they infect.
But they're not very infectious.
But other viruses that people might view as less threatening and, mistakenly, a lot of people view influenza as like a common cold virus, but they are mistaken.
Because that is the single virus that can take off from any spot in the world.
You've seen it take off from Mexico.
It can take off from any spot in the world, circumnavigate the world in a matter of months and cause untold devastation.
Viruses can transmit so effectively that they have infiltrated every living species in the world, and we are no exception.
I think it is remarkable, each person walking by has a plethora of viruses in them.
They have at least four viruses, everyone, me included.
We will have an enterovirus, a chicken pox virus, a herpes virus, a wart virus as well.
Throughout our lives, we suffer a continuous onslaught.
Over a lifetime, one would be attacked by probably 500, 600, 1,000 different viruses of all kinds of families.
Each of these has a different way to attack its host.
HIV appears to be particularly cunning.
HIV is the king of clever viruses.
It replicates in the kinds of cells that are designed to detect and destroy incoming viruses in the human body.
So, it's perfect.
Others go for different parts of our bodies.
Some viruses are transmitted sexually and they cause lesions in that area of the body.
Other viruses spread around the whole body, like smallpox.
Fair enough, the virus is exemplified by all the pox, but really, that's not killing you.
What is killing you is the virus replicating in your internal organs.
The most deadly virus of all hides in dogs, rodents and bats.
Rabies is probably the only virus that I know that can cause death in 100% of victims.
The reason for that is, of course, it invades the central nervous system.
It might take a long time to do it.
It will depend where you were bitten.
If you're bitten on your arm, it will take quite a long time for that virus to move up the nerve system to the brain, but in the end it will.
It might take two months or three months, but in the end, rabies will get to your central nervous system, replicate, destroy cells in the central nervous system and that will give you the symptoms of hydrophobia, dizziness, all the symptoms that will in the end kill you.
Respiratory viruses like SARS or influenza replicate in the airways and air sacs of our lungs causing an immune reaction.
It's when this response escalates that it causes problems.
These are people that, for some reason or another, have not managed to contain the virus well in the nose and throat, which is where the virus entered their body, and the virus has then managed to penetrate deeper into the lung.
There it's destroying cells of the lung that are important in helping the lung work and it's also of course triggering an immune response to itself, which is clogging up the lungs and stopping the lungs from doing their job as well.
And the people are dying of pneumonia.
Every virus has its own little way of digging in.
Every virus has its own little way of replicating and you have your way of responding.
The combination sometimes is overwhelming.
Although viruses infect each and every one of us, somehow life continues.
That's because if a virus has been around for a while, our immune systems have a chance to adapt and build up protection.
The viruses that do most damage are the ones that are new to us.
But these don't come along very often, for the simple fact that most viruses don't belong in humans.
A lot of human viruses and particularly the most important ones - hepatitis B, for example, HIV, influenza - they came from the animal or bird reservoirs on this planet.
I think in influenza, it's not basically a human virus.
It can be humanised, but basically at heart it's a bird virus.
At heart it loves to be in a great migrating swan, in a duck, in a goose.
It doesn't really want to be in humans, I think.
Avian flu can be mild in a bird, but fatal in a human.
But for a virus to move from infecting an animal to infecting a person, it has to overcome a massive barrier.
The biggest hurdle they have is what's called the lock and key problem.
That is, it's got to latch on to a human cell.
I mean, with influenza for example, I mean, here's an influenza virus, it's got its little latch here on this protein here.
Right at the tip of this protein.
Because if this virus is living in a migrating bird for example, the little tip here is always adjusted so that the virus can infect bird viruses, other birds.
And that small protein tip is what stops the virus from infecting us.
Most of the time.
It has a big difficulty, because it won't fit onto a human cell.
And so it has to mutate along the tip here.
And by chance, you'll have a mutation here.
A change at the tip which enables one particular virus, on one particular day, in one particular place to latch on to a human cell in a human.
From that chance event, viruses can jump the species barrier and get a foothold in human populations.
Nowhere is this more vividly experienced than here - the Democratic Republic of Congo.
This region of jungle is the front line of our battle with viruses.
Some of the most dangerous diseases in history have jumped into humans from these rainforests of central Africa.
In the last 20 years, there've been a number of viruses that have been discovered in these areas, including Ebola and monkey pox.
HIV has also come from this area.
So, there could be thousands of other viruses out there and we have no idea what they are, how they spread and what populations.
Epidemiologist Dr Anne Rimoin is in search of the next disease threatening to cross species.
It's called monkey pox.
Well, monkey pox is a disease, it's a cousin of smallpox.
It's found in animals, originally, and not in humans.
What makes this area so fertile for fatal human viruses is that humans here interact so closely with wild animals.
Monkey pox is found in a lot of the local monkeys and squirrels and some of the rodents that people eat on a day-to-day basis here.
GUNSHO It's this close contact between monkeys and humans which gives the virus opportunities to spread.
ALL CHAT IN FRENCH They're very, very forcefully, they were saying yes, indeed.
They eat it every single day.
And, in fact, if they don't eat it, they lose power.
They're less forceful.
They're less able to work.
So, we're saying you have to be very, very careful with these monkeys because you can see that there are, these teeth are very, very sharp.
And so you can see it's a very easy way for viruses to spread between humans and animals.
People are cutting these animals, there's blood everywhere, they're getting bitten and scratched by these animals.
This is just a very typical scenario of how viruses can cross species between animals and humans.
Monkey pox is a devastating disease that kills up to 10% of people it infects.
We're looking for pock marks.
You can see some pock marks here, here He has another scar right here as well.
Here, here Cases of human-to-human transmission have occasionally been recorded.
But at the moment, it's mainly those who have direct contact with infected animals who contract it.
They found dead squirrels, brought them home, they ate them and they all ended up getting monkey pox.
So, they didn't get monkey pox from each other.
They got it all from the same source at the same time.
It can be passed from one person to another.
There have been documented up to eight serial transmissions, meaning that up to There have been up to eight generations of monkey pox passed from one person and then onto the next person, on to the next person, on to the next person.
It's because the monkey pox virus is only limitedly contagious between people that it's currently contained here in central Africa.
But if it does evolve to pass freely from human to human, the way we live today makes its spread inevitable.
As people and populations become more urbanised, viruses will more easily find themselves into urban centres, like here in Kinshasa, and then, through international travel, be spread throughout the world.
Our first lines of defence remain intelligence of emerging diseases and containment when we find them.
There's no way to prevent viruses from emerging.
New viruses emerge all the time.
The question is, are we aware of them or are we not? So, the only way we're going to know is if we have good disease surveillance.
For example, if we had known about HIV early on, we would have been able to do more to prevent the spread of HIV in populations.
Here in Congo, for example, the first case of HIV that was reported was in 1958.
Now, that's based on recent analysis.
It wasn't in 1958, we didn't know But if in 1958 we had known that HIV was lurking in populations, we might have been able to do more to be able to prevent what's happened and having it become a worldwide pandemic.
But we're not totally defenceless.
For some viruses, we have vaccines.
It's quite possible that this man has saved more lives than anyone else alive today.
His team fought a battle against one of the deadliest diseases we've ever encountered - smallpox.
Oh my God.
Oh my God.
What a life.
Disgusting.
Awful.
Ugh.
No.
Oh my God.
This little girl, my goodness.
Look at these lesions here.
They're just almost all bumping against each other.
The mother holding a baby again with a quite extensive rash.
The baby has a face that's swollen.
He's got a lot of pustules there.
He looks miserable enough.
And in a young child like this, I think the probability of death is fairly high.
The smallpox virus kills about one in every three people who catch it.
Smallpox, throughout history, has been the world's worst pestilential disease.
And it was greatly feared everywhere.
There are approximately 10 million cases a year and about 2 million deaths.
Not only deadly, but also highly infectious.
Smallpox is transmitted from person to person really with droplets.
An individual with the disease and the rash has the rash inside the mouth and little pustules.
He speaks and the droplets are expelled and there's a smallpox virus, so you inhale the virus and that's the way you get the disease.
Just by talking to somebody.
Yet smallpox is one of the few viruses for which we have a vaccine.
Using an agent that resembles the virus, the vaccine stimulates the body's immune system to recognise the real virus in future, protecting you from infection.
And there is one other feature of the smallpox virus that makes it vulnerable.
It's been circulating in humans for so long, it's lost the ability to infect other animals.
It's only possible host is us.
Back in 1967, the World Health Organisation realised this presented a strategic opportunity.
If they could vaccinate enough people, they would leave smallpox nowhere to go.
Nowhere to hide.
So a WHO team, headed by DA Henderson, hunted down outbreaks of smallpox and vaccinated everyone who might be at risk.
Considering the 10 million infections per year, it was a daunting task.
But just a decade later, smallpox was completely eradicated from the community.
We felt we had finally won a real battle.
We'd outwitted the virus and eventually removed it from the face of the Earth.
The eradication of the smallpox has got to be one of the great achievements of mankind.
The co-ordination that a vaccination campaign like that takes is just incredible.
In the 20th century, 300 million people died of smallpox.
It's the only human disease that has been eradicated and one cannot really estimate the value of this to mankind.
The smallpox virus presented a unique set of biological circumstances that meant it could be eradicated.
Other viruses have abilities that smallpox doesn't.
They can change their structure, so they're always one step ahead of a vaccine.
They can mutate.
And one virus does this with incredible efficiency.
About twenty years ago, I felt fine about life.
I felt good about life.
My partner and I were expecting a baby in '92, and I was full of excitement about that.
I think he was feeling a bit terrified! In 1992, Alice Welbourne already had two children.
Her GP recommended several routine antenatal tests.
She phoned me up, I guess a week or so later, and I could just tell by the tone of her voice that something serious was up.
And I went in and I sat down, and I can still remember the Venetian blinds, you know, those horrid grey metal Venetian blinds, across the window.
And she just said, "It's HIV.
Everything else is fine.
"It's the HIV.
" It was just completely devastating, because I was completely fit and well.
I had no realisation at all that I might have anything the matter with me and instantly thought, "OK, well, I'm obviously just going to have to prepare for my death.
" HIV is able to pass under our immune radar.
Thousands of virus particles can infect human cells, initially without a person even being aware.
They then quietly multiply, undisturbed, in Alice's case threatening both her and her unborn baby.
We made the decision that we were just going to have to go ahead with a medical termination, and that's one of the toughest decisions I've ever had to make in my life.
HIV has a particular strategy that's meant it's beaten our attempts to produce a vaccine.
HIV mutates at an alarming rate.
As it copies itself, it's continuously changing.
One of the reasons that vaccine development against HIV is so difficult is that, like influenza virus, it can change and makes mistakes, it's sloppy.
You might think that's a bad thing, but actually it's not.
If you're a virus, it's very good.
The genes of HIV can be represented as a series of letters.
Once the virus gets into us, it copies itself.
But because it's constantly making mistakes, some of the offspring will be different .
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presenting our immune system with an enemy that is never quite the same.
So it's a very quick and dirty strategy that viruses like to use in order to be able to change rapidly in response to things we throw at them, like drugs and vaccines.
So that if we did make a vaccine against one particular strain of HIV, there would be so many others appearing rapidly that the vaccine really would not be effective.
There is now a successful treatment for HIV, using antiretroviral drugs, but these, too, have to overcome HIV's ability to mutate.
Whilst single antiretroviral drugs don't work for long before the virus acquires resistance, a combination of three different drugs at the same time can overcome this.
For Alice, the nine years of taking them has had a remarkable effect.
I've probably got as good a life expectancy here in the UK as anybody else of my age.
But it's a constant battle.
The virus can still mutate and become resistant to these drugs.
You know, we have so much science, we have so much technology, the assumption is there that surely we ought to be able to control viruses.
But of course, what having HIV has brought home to me is how unreal that illusion is, and how we are all living on the edge.
HIV's ability to endlessly mutate and evade our immune system has so far caused the death of over 25 million people.
Today, more than 35 million people worldwide live with the virus.
An ability to mutate is what defines some of the most successful viruses, including H1N1.
Against an individual virus, you can clearly make a vaccine, and we know how to do that, and we are making a vaccine at the moment for H1N1.
But then the virus will change, and next year we'll have a slightly different virus, or some time in the future we may have a radically different virus.
So we're always having to make new vaccines to combat the new strain that arises.
Alongside mutation, influenza exploits another ability of viruses.
We can be infected by more than one virus at a time.
And if these viruses meet, they can swap their genes around, giving birth to totally new viruses.
This process is called re-assortment.
It's formed by two swine viruses co-infecting the same cell, shuffling their pack of genes, and a new variant coming out that has got genes derived from both parents.
That's what I like to call "viral sex", because it's like two parents mixing their genes up together and making a new type of progeny.
In the case of H1N1, swine flu, it was a multiple re-assortment.
What we can sum up with swine flu is that it's got two genes that were very recently in a bird virus, it's got one gene that was very recently in a human virus, and then the remaining genes were recently in pig viruses, but in two different pig viruses that were in two different continents.
In an instant, this re-assortment created a new virus that was able to infect humans, one that was shockingly new to our immune systems and highly infectious.
This could be the first flu pandemic for over forty years.
Swine flu went from a few isolated incidents in Mexico in mid-April 2009 '.
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advising caution when travelling to the affected areas.
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to a worldwide pandemic in just two months.
The first case of swine flu in Europe has been confirmed in Spain.
Swine flu has now spread across at least five countries.
The Health Protection Agency says as many as seven hundred potential cases are being investigated.
The World Health Organisation says swine flu has now spread to nearly every country in the world.
But whilst highly infectious, it wasn't as dangerous as feared.
For all our modelling, we were still unable to predict the effect of the pandemic with any accuracy.
'The swine flu pandemic is considerably less lethal 'than had been feared.
' But maybe that shouldn't have come as much of a surprise, because the one thing viruses don't want to do is kill us.
I think viruses don't really want to kill us, if you see what I mean.
It's not much advantage to them if they're replicating in us and suddenly we fall over the table.
You know? They can't transmit onto someone else.
Every virus has to strike a fine evolutionary balance between being able to replicate successfully and multiplying so much it destroys its host.
In reality, when you go and look in nature, you actually see that many viruses don't kill their hosts.
They've evolved with their hosts so that they're living in a wonderful symbiosis of being able to still replicate without destroying their host, because it really doesn't make any sense to kill the home that you need to make more of yourself.
You know, even the viruses beloved of medical students like Ebola, Lassa, they're not huge killers.
They're not killing 80% of people or anything like that.
So it's a very exceptional virus that kills more than about ten per cent, and most viruses kill many, many, many fewer than that.
The most successful viruses infect millions but kill few.
On that basis, swine flu, with its high levels of contagion but relatively low death rate, is, arguably, successful.
But that's not to say there may not one day be a flu virus that can kill millions.
The current viruses can mutate and give new strains, but also there's a fantastic opportunity for new strains to come along that we don't have immunity to.
The question is, what's going to be the next pandemic? Already we're thinking about the next one.
For that day, we need to be ready, and one man is doing all he can.
Professor Eckard Wimmer had an incredibly simple idea.
He believed if he were able to build a virus from scratch, we would learn so much about how they work it would open new opportunities to create vaccines or even cures.
But to achieve this would mean attempting something highly controversial that had never been done before.
Professor Wimmer would need to recreate life itself.
That's what I was called.
I was Frankenstein in one of the papers.
Except they said I was Little Frankenstein, and I was insulted.
In 2002, Eckard Wimmer realised viruses are simply strings of chemicals.
This is the formula for the polio virus.
He wondered whether they could mix a set of these chemicals together and recreate the living, reproducing polio virus just from its basic ingredients.
We were nervous about that.
You're doing an experiment nobody else had done, and so there's always a possibility of a surprise.
Like all viruses, polio is simply a collection of genes protected by a shell.
In the case of polio, this genetic material is made of chemicals similar to DNA, called RNA.
It's this long string of genetic material that Wimmer was trying to make.
The problem was, they needed 7,500 pieces of RNA in an exact sequence.
So, what do you do? You cut up the 7,500 nucleotides on the computer, actually, you do it on the computer.
You cut them up into smaller pieces.
In fact, you mail order them.
All Professor Wimmer had to do was call up a commercial laboratory, order his gene fragments, and wait for the post.
From these fragments, they had to assemble the complete genome of the polio virus piece by piece.
Whilst complex, this stage was nothing new.
It was the next part that was controversial.
They had to make this collection of genes live.
And now we had this RNA, and we had to kick the RNA into behaving like a biological entity.
As you say in the computer language, we had to boot life into this biological program.
We took this RNA, and mixed it with a cell-free juice.
That juice was produced from human cells which we opened up.
We threw away the nuclei and mitochondria which are large organelles, and were left with an almost clear juice still containing lots of goodies that the cell has in the cytoplasm.
And now we took the RNA and mixed that with that juice.
Lo and behold, the RNA woke up.
This was really remarkable.
The mail-order collection of RNA, simple chains of chemicals, started building more copies of themselves and then new shells, and then these component parts assembled themselves into new virus particles.
We had synthesised a virus particle outside living cells, thereby violating the dogma that viruses absolutely need a living cell environment in order to replicate.
These home-made viruses were identical to the natural viruses.
Eckard Wimmer had re-created life and opened the doors to whole new areas of learning.
In terms of what Eckard Wimmer was the first to do, which was to create a virus from a piece of synthetic DNA, that has already massively changed what we can study in terms of viruses and, therefore, our ability to ultimately combat them.
The ability to tailor-make vaccines to new viruses as they arrive, the ability to understand, at every detail, which bits of the virus make it more or less pathogenic and be precise about it, because of what Eckard Wimmer did, it has revolutionised the field.
It is a huge breakthrough.
Discoveries like this have brought us as close as we have ever been to understanding and controlling viruses.
But constraining viruses completely, if even possible, is an impulse we should resist.
Viruses actually have been very important in the development of you and me.
So on the one hand, we still have the enemy.
On the other hand, we know viruses have been good for us.
It's a sentiment shared by many.
Our lives and viruses are intertwined.
They are a major and important component of all ecosystems of this planet and I don't think anyone could imagine how life could have evolved, or could even operate today without the presence of viruses.
And all life includes us.
We don't know, actually, how much we are dependent on the viruses that infect us.
Or replicate in us.
We think of them as pathogens, but actually, we very, very likely are highly co-evolved together.
Our immune defences have been shaped by the threat of viruses.
But, equally, the threat of our defences make the viruses evolve.
Science is beginning to reassess our relationship with viruses and their role in shaping life on Earth.
And I like to think that we're actually here to support the replication of viruses and everyone's been thinking of this backwards.