Viruses can often be seen in a very poor light, but they aren’t all bad. In fact, we humans probably wouldn’t exist without viruses. Author Michael Brooks writes about the upside of sharing the planet with these ruthless killer machines. Here are the top 10 reasons to love viruses. Ah-Choo!

10. The virus gave us complex life

Evolution’s greatest innovation – the cell nucleus – is thought to have come from a virus (http://www.sciencemag.org/cgi/content/summary/305/5685/766). The cell nucleus and a virus are packaged DNA encased in a protein coating. In some relatively simple organisms, such as red algae, the nucleus can move between cells in a manner that suggests the mechanisms of viral infection. While bacteria package their DNA in circular chromosomes, cell nuclei and viruses use linear packages. The evidence is not yet conclusive, but extremely suggestive. And if an opportunistic virus had one day infected a bacterium and taken control rather than destroyed it, it would certainly have outcompeted anything in the neighborhood.

9. The best one comes from Bradford

Ok, so that’s not a very scientific take on why we should appreciate the virus. But there’s a certain poetry to the fact that, while gene pioneer Craig Venter was sailing the exotic Sargasso seas in search of new viruses, the biggest shakeup in virology came from a monster found in what may be England’s least glamorous town. Mimivirus was discovered in 1991, in the water of a hospital cooling tower as Bradford’s public health officials searched for the source of a particularly nasty pneumonia outbreak. Mimivirus was so big – 30 times as big as the virus that gives you a cold – microbiologists thought it was a bacterium at first. It also contains far more DNA than scientists associate with viruses.

Mimivirus is particularly fearsome because it is virtually indestructible. But infection by mimivirus is survivable. A technician in a Marseille hospital who was working with the virus accidentally infected himself. It gave him an unremarkable bout of pneumonia, and he’s all better now.

8. Almost all our DNA comes from viruses

Around 8 per cent of your DNA is unmistakably viral in origin. Between 40 and 50 per cent is suspiciously virus-like, and most of the rest of our genes behave like viral genes, replicating in much the same way. It seems we are, in many respects, the product of viral activity. Who do you think you are? If you’re looking for your ancestors, you could do worse than look to the oft-reviled virus.

7. They have unknown potential

When Craig Venter, the human genome pioneer, took samples of the Sargasso Sea, his team found more than 1800 new species of virus containing more than 1.2 million new genes . Every 200 litre bucket contained millions of viruses never before seen by humans.But that’s nothing: a milliliter of water from Lake Plussee in Germany was found to contain 254 million virus particles. It could prove rather useful in healthcare: estimates suggest there are more bacteria-killing viruses in the biosphere than all other life-forms put together.

6. They drive scientists crazy (are they alive or not?)

No one can agree on whether viruses should be considered part of biology, or chemical parasites on biology. They contain genetic material, but rely on other creatures to process it. To complicate matters further, many viruses contain more genetic material than some bacteria, and bacteria are definitely part of the living world. So, depending on which definition of life you choose – and there are many to choose from – viruses can be thought of as part of the biosphere or just plain old chemistry.

5. They haven’t always been parasites

As scientists discover more and more viruses, they are analyzing the DNA inside their protein crystal heads and finding that viruses may once have had an independent existence The trunk of the tree of life is supposed to be split into three branches. The eukaryotes are the advanced organisms whose large and complex cells contained a nucleus that held inheritable information. The bacteria have cells without a nucleus. The archaeans are a bit like bacteria, but have a distinct genetic heritage, and are often found in extreme environments, such as hot springs. Genetic evaluations of viruses suggest they evolved before this split occurred, in which case the parasitism may be a later development.

4. They are the driver behind evolution

The way viruses cut and paste DNA has led them to create the diversity essential to evolution by natural selection (http://cvr.bio.uci.edu/learn.html). Many viruses do not just replicate at will and destroy their hosts, but insert themselves into the host’s genome and replicate only when the cell divides. Genetic analysis of every living organism has revealed the presence of viral DNA, and occasionally this is useful information that encodes something the cell can use. In this scenario, viral DNA can radically alter what an organism does – leading to new evolutionary directions.

3. They can beat antibiotic-resistant bacteria

Doctors have known for around a century that viruses can be used to kill bacteria. In 1917, for example, Canadian microbiologist Félix d’Hérelle cured children of dysentery overnight by giving them a solution containing bacteria-destroying viruses. In the age of antibiotics, however, viruses were left on the sidelines. With the advent of antibiotic resistance, the viruses are coming off the bench. Bacterium-eating viruses have been harnessed by researchers at University College London to deal with particularly problematic ear infections, for example . It is not yet clear whether bacteria can evolve resistance to attack by virus.

2. They can deliver gene therapy

Viruses have been used as carriers to transfer genes into the eyes of four people who suffer from hereditary blindness. The result was significantly improved sight. The hope is that disabled viruses can be used to treat many genetic diseases. Viruses are also being used to deliver genetic material that can help cure AIDS.

1. Viruses might cure cancer

Reovirus, which is relatively harmless to humans, is in trials as a “booster” for anti-cancer drugs. It works by infecting cancer cells that have a mutated form of the Ras gene. The mutated Ras causes runaway cell growth, but also makes the cells vulnerable to the virus. Trials show that reovirus kills these cells, helping anti-cancer drugs do their work.

Researchers in a Nagasaki hospital have found that a virus that occasionally cause leukemia seems to cut the chances of developing stomach cancer by one-third

Epstein-Barr virus, which is carried by 90 per cent of people worldwide, produces no symptoms in most of us. Sometimes, though it can lead to a leukaemia-like cancer called Burkitt’s lymphoma (http://www.cancerhelp.org.uk/help/default.asp?page=119#viruses). But the virus can also be used to battle the cancer. It produces enzymes that can be tagged with radioactive molecules to make the cancer show up in scans. And studies show the virus’s hijacking of cell machinery can be used to burst and kill tumor cells.

Michael Brooks is a consultant for New Scientist magazine, and the author of 13 Things That Don’t Make Sense: The Most Baffling Scientific Mysteries of Our Time . Article was reprinted from http://www.timesonline.co.uk

Photo by xaminmo

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