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Other Fun Stuff

Could Ebola and cold viruses combine to make some sort of supervirus?

-A curious adult from California

November 20, 2008

Sounds like the perfect weapon for a bunch of terrorists. A virus that kills almost everyone it infects and spreads as easily as a cold. Yikes!

Lucky for us, this sort of virus won't be appearing anytime soon. Mother Nature almost certainly won't create such a thing. And scientists don't have the skills to make it in a lab either.

To understand why we shouldn't lose any sleep over this, we first need to learn a bit more about viruses. Then we'll be able to see why neither nature nor scientists can easily mix and match viruses to create superviruses.

Viruses

Viruses are pretty simple. So simple in fact that scientists don't even consider them alive.

Most viruses are made of only two parts. First they have some genetic material (RNA or DNA). This is the part of the virus that has the instructions for making new viruses.

The second part is an outside protein shell. This shell protects the genetic material. Sometimes it is also used to get the DNA or RNA into a cell.

And that's all there is to most viruses. But even something so simple can do a lot of damage.

Once a virus injects its DNA or RNA into a cell, it forces the infected cell to make new viruses. These new viruses then go on to infect new cells. This cycle keeps repeating until the body defeats the virus. Or the virus defeats the body.

Usually only one kind of virus infects a cell at any one time. Sometimes, though, two different kinds of virus can infect the same cell. This can sometimes result in a new virus made up of parts of the other two. But this only happens in very special cases.

One such example was the Spanish flu. This disease spread worldwide right after World War I and killed upwards of 25 million people.

The virus that caused the Spanish flu didn't exist before 1918. Experts think that it was a mix of human and bird flu viruses.

Most likely someone was infected by both a bird and a human flu virus. The bird flu probably picked up some parts from the human virus that made it easier to spread and harder for the body to fight off.

But, this kind of thing can't happen with the cold virus and Ebola. To be able to do this kind of mixing and matching, the viruses need to have very similar genetic material. And the cold virus and Ebola do not.

Recombination

Mixing and matching of genes is called recombination. It can only happen between two pieces of DNA or RNA that have sections that are very similar. This is so the two pieces of genetic material can line up with each other and swap at these points.

On the right, imagine the human flu virus RNA is in blue and the bird flu is in red. Their RNAs are very similar except for a couple of spots. These differences make a bird flu able to infect a bird. And a human flu a human.

I have marked one of these differences with an asterisk. Notice that the rest of the regions are very similar. The similar regions can line up and recombine at the black X's, resulting in something like this at the bottom.

If the recombination pops the right regions from the human flu virus to the bird virus, we get a bird virus that can easily infect people! Our bodies have never seen a bird flu before and so aren't very good at fighting it off. Which is why it is so deadly.

But this won't work with Ebola and the cold virus for a couple of key reasons. First, Ebola and the cold virus have very few pieces of their RNA that are similar enough for recombination to take place. Since it isn't easy for the two RNAs to match up, they can't easily recombine.

And even if by some miracle they managed to recombine, the resulting virus would almost certainly not be dangerous. Why not? Because of genes.

The instructions for making new viruses are contained in a virus' genes. Each kind of virus has a different set of genes arranged in a different way.

What this means is that when two very different viruses recombine, the new virus will have a jumble of genes. Some genes needed to hijack a cell might go missing. Or those needed to make the outside of the virus might go missing.

Or there might be duplicates of genes so that a mix of two shell proteins gets made. Or any number of other possibilities. The end result will almost certainly be something that can't do much of anything. And certainly not be a killer cold/Ebola virus!

While this is pretty much impossible in nature, it might be possible in a lab. Maybe someday in the very distant future that is...

Intelligent Design

In the past few years, scientists have been able to create life (sort of). For example, at the beginning of 2008, scientists made a bacteria's DNA from scratch. Then they stuck it into a bacterium. The bacterium now used this new DNA as its instruction manual. Voila, life.

Scientists have also created viruses from scratch. Because they are so simple, this is even easier than making a bacterium.

Scientists had to stitch together 580,000 DNA letters in the right order to make a bacteria. An Ebola virus only takes 19,000. And a cold virus 7,200!

So scientists can pretty easily make an Ebola virus or a cold virus in the lab. But combining them into a supervirus is a whole different story. Ebola and the cold virus are completely different shapes and sizes, and the way they infect are so different that you can't just mix their genes.

You would first have to figure out for each virus exactly how each gene works, and how the genes work with each other. This is a very complicated process. Scientists have been working on a bacteria virus for over 50 years and they still don't know how all the genes work and how they work together. They've been working on Ebola and cold viruses for much less time.

Not only that, but viruses can't have a lot of extra genes in them. They're built for small size and so it isn't easy to add genes to an Ebola or cold virus. You can only add a gene if you subtract something else. It would be very difficult to know the right genes to subtract and the right ones to add back.

So I would say that the kind of virus you describe could only be made in a lab in the distant future (if ever). For now, I would be more worried about the kind of stuff that can be mixed up in nature, like HIV or viruses like the Spanish flu!

*The cold virus is icosahedral in shape (it has 20 sides) with the protein coat enclosing its genetic material, RNA. It's only about 20 nanometers in diameter -- you could put 50,000 viruses on end and it would only be 1 mm! But the Ebola virus is tubular, like a long worm. It's over 1000 nm long, 50x longer than the cold virus and 4x wider! It also has about 2.5x more RNA.

By Julia Oh, Stanford University


A killer Ebola/cold virus is very unlikely.


Viruses can only swap genetic material if they are very similar.


The cold (blue and red) and Ebola (green) virus have such different shape, size, and amount of genetic material that the odds of a successful cross are close to zero.*