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Virus Invaders

Here's how to outwit the annoying – sometimes devastating – viral invader. The first step is to understand its game plan

You're pushing the trolley around the supermarket and absentmindedly rub your nose. It's something we all do all the time. What you don't realise is that with this simple action you've exposed your body to a microscopic invader so potent that in 12 hours you'll be flat on your back in bed.

The person who last used the trolley has a cold. On their way down the same aisles, they sneezed and politely covered their mouth with their hand. Within the droplets that flew from their mouth were thousands and thousands of virus particles, which were then deposited on the trolley handle. Minutes later you picked them up and transferred them to your face.

Inside the moist environment of your nose, the virus particles are swept to the adenoids, in the back of your throat, where they invade cells, reprogramming these hosts to help the virus reproduce. Eventually these cells rupture, releasing thousands of new viruses.

Less than half a day later, your throat is aching and sore, your head's pounding and you know you should be in bed. You leave work but on the way out you sneeze, wipe your nose and put your fingers on the door handle . . .

It's the stuff of Hollywood – an alien invasion of your cells. Films such as I Am Legend and Outbreak have taken the consequences of a viral outbreak to the extreme, but in reality there is a horror movie going on inside our bodies whenever a virus takes hold.

Recent global alarm over swine flu has drawn attention to how rapidly viruses can free-ride around the world, but the truth is that all manner of viruses exist in the air, on surfaces, even on our own bodies all the time.

More than 200 of them are responsible for the common cold alone – rhinoviruses, coronaviruses, adenoviruses and respiratory syncytial virus are all to blame. Just as your body builds immunity to one of them, you get invaded with another and down you go again.

Goodies and Baddies
Many viruses are well adapted to live in our bodies and never cause problems. Some 80 percent of us are infected by the glandular fever virus by the time we're 50. The herpes simplex virus, responsible for cold sores, lives quietly in the nerves at the back of the brain and only comes out to cause trouble when you're stressed – and periodically it's secreted in your saliva so that it can move on to invade the next body.

Others are more dangerous. The viruses responsible for deadly ebola, severe acute respiratory syndrome (SARS) and avian influenza regularly hit the news, while millions of people die every year from viruses that cause respiratory or gastrointestinal illnesses. HIV/AIDS has decimated much of the world, and governments are preparing for the next great influenza pandemic – we've had three in the last century.

Yet for something that has such a major impact on humanity, the tiny virus is little understood. Despite progress in developing antiviral drugs in the past ten years, there's still very little we can do to treat a viral infection.

It's frustrating for doctors. Most people expect to be cured, but viral infections can't be helped by anti-biotics. Says Sydney doctor, Ruth Ratner. ''They'll say ‘I thought if I came to you early you could do something.'?''

Know the Script
One family knows all about viruses. Recently, Muhammad Joehan Bin Rohani drove to Singapore from Kuala Lumpur to drop off his two oldest children at his mum's for the school holidays. A day after arriving, eldest son, eight-year-old Nuqman, got chicken pox. Two weeks later, his younger brother Ammar was infected. Days after that, their two aunts also came down with flu-like symptoms and lesions all over their bodies. Two weeks later, Joehan too fell ill with chicken pox.

''In a span of six weeks, five of my family members got infected with the virus. Once the first case happened, we knew it was a matter of time before the rest of us would get it,'' says Siti, the boys' aunt.

Viruses only became a problem when people started to live in large communities – small, isolated tribes are relatively protected. That's why children are particularly vulnerable – they mix with lots of other people and their level of hygiene isn't as good as those of adults. The good news: children tend to get less sick than adults when exposed to the same virus for the first time.

Viruses are very tiny pieces of genetic information surrounded by a protective coating. ''The only ultimate purpose of a virus is to replicate itself,'' says Professor Chris Burrell, head of the Infectious Diseases Laboratories at the Institute of Medical and Veterinary Science in Adelaide, Australia.

Up to 100 times smaller than a bacterium, viruses cannot reproduce while they are outside a living body. But as soon as they invade a host cell they inject their DNA or RNA into it so they can behave like living organisms, reproducing and mutating.

''Viral nucleic acid is like a computer program,'' Professor Burrell explains. ''It's the genetic blueprint. The virus particle is like a CD that's learnt the skill to jump from one computer to another and to use any means necessary. Once inside the computer it programs the computer as if it was alive. The core of the whole thing is the information in the program.''

You might not get sick the moment a virus enters your body. After they're infected with HIV, people have a rash and fever, then recover. But unknown to them, the virus starts replicating and killing off T-lymphocyte cells while the body madly replaces them. It's only when the body runs out of these cells, sometimes years later, that the disease kicks off again.

Survival Skills
Through evolution, viruses have worked out clever ways of replicating themselves. Many use animals as hosts to travel large distances – bats, for example, are thought to carry a range of viruses and do a great job because they're sociable animals. Other viruses aim for specific cells – the viruses that cause influenza need cells in the respiratory tract, while those responsible for hepatitis search out liver cells.

Viruses' survival is dependent on finding new host cells and replicating; viruses that can't do this in time, very quickly disappear. In Philadelphia, yellow fever decimated the population in the late 18th century when virus particles were transported by mosquitoes. Suddenly the temperature dropped, the mosquitoes died and the disease was over within a month.

There's another trick that viruses have up their sleeve: they mutate. Take the HIV virus. Every time it infects a new human, it slightly changes its composition. ''HIV is like a snowflake, every one is different,'' says Professor Burrell. ''HIV1 and HIV2 are closely related but clearly different. Within each of these, there are a number of subtypes of 1 and 2, and within each subtype there are lots of different strains. So in each infected human there might be 50 or 100 slightly different strains.''

That means there are often outbreaks of new, unrecognised viruses. And that is what worries governments: global travel means viruses can spread round the world in a flash. New nasties include Hendra horse virus in Australia and Nile virus in the US, while changing climates may mean viruses that were once confined to the tropics, such as Japanese encephalitis, may arrive elsewhere soon. Last year, the nasty mosquito-borne Chikungunya virus hit Southeast Asia.

Birgit Bradtke has lived in the remote Kimberley region in Western Australia for 15 years and knows that when it has rained and the little mosquitoes are out, she's at real risk. One night she was bitten badly at dinner and joked, ''I bet I'll get Ross River Fever now.'' Three days later the symptoms set in: painful joints, chills, exhaustion. ''If you live up here you're familiar with the symptoms,'' she says.

Carried by marsupials and spread by mosquitoes, Ross River Fever infects around 5000 Australians every year. Birgit was lucky: she recovered quickly, although it still reoccurs occasionally when she's feeling run-down.

There's another trick that viruses have up their sleeve: they mutate. Take the HIV virus. Every time it infects a new human, it slightly changes its composition. ''HIV is like a snowflake, every one is different,'' says Professor Burrell. ''HIV1 and HIV2 are closely related but clearly different. Within each of these, there are a number of subtypes of 1 and 2, and within each subtype there are lots of different strains. So in each infected human there might be 50 or 100 slightly different strains.''

That means there are often outbreaks of new, unrecognised viruses. And that is what worries governments: global travel means viruses can spread round the world in a flash. New nasties include Hendra horse virus in Australia and Nile virus in the US, while changing climates may mean viruses that were once confined to the tropics, such as Japanese encephalitis, may arrive elsewhere soon. Last year, the nasty mosquito-borne Chikungunya virus hit Southeast Asia.

Birgit Bradtke has lived in the remote Kimberley region in Western Australia for 15 years and knows that when it has rained and the little mosquitoes are out, she's at real risk. One night she was bitten badly at dinner and joked, ''I bet I'll get Ross River Fever now.'' Three days later the symptoms set in: painful joints, chills, exhaustion. ''If you live up here you're familiar with the symptoms,'' she says.

Carried by marsupials and spread by mosquitoes, Ross River Fever infects around 5000 Australians every year. Birgit was lucky: she recovered quickly, although it still reoccurs occasionally when she's feeling run-down.

Viruses can kill, cause permanent disability, or just make our lives a misery. They may also lead to other diseases. Better understanding of viruses' role means we now know 20-25 percent of cancers have a viral infection as a risk factor. If you contract hepatitis B or C, for example, your risk of liver cancer sky rockets. Human papillomavirus (HPV) leads to cervical cancer, and Epston Barr virus to lymphoma.

Some researchers are drawing an even longer bow. In 2000, American scientists linked adenovirus-36 with obesity – infected animals got fat without eating more, with further evidence in 2007. Viruses have also been linked with multiple sclerosis, high blood pressure during pregnancy, pre-term birth and Alzheimer's disease.

Most of these theories need research before they're proven. But if viruses are responsible for a host of other diseases, that's good news, says Professor Collignon. ''It means we can come up with a vaccine and prevent it, which will help future generations.''

Potent Weapons
The problem with treating viruses is that they merge with the host cells before eventually destroying them. That means if you kill the virus, you also kill off the cells – that's why so many antiviral medications are toxic or have side effects. We already know how to kill viruses that cause the common cold, but the side effects are too great to warrant their use.

However, we have two potent weapons to combat viruses: antiviral drugs and our own antibodies.

In the past 20 years we've made great strides with antiviral drugs. Technology is enabling us to understand the complex functioning of viruses like never before, and to develop new drugs to stop them reproducing. Unlike viricides, which kill viruses in their inactive phase outside the body, antivirals work by identifying the part of the virus's protein that can be disabled.

Antivirals work by preventing the virus from entering a cell (like amantadine and rimantadine for influenza), by deactivating it after it enters (Aciclovir for herpes or Zidovudine – AZT – for HIV), or stopping it from releasing new virus cells from the host (Relenza and Tamiflu for influenza). The other way is to stimulate the body's own immune system – interferon, which combats hepatitis, is in this category.

With a further 20 or 30 promising antivirals now in development, are we winning the battle against the microscopic invaders? ''The drugs we have aren't always that effective, and resistance is developing,'' says Collignon. He says that Tamiflu still only shortens the illness a day or so. ''That's better than nothing, but at the end of the day prevention is what it's about.''

Protect and Survive
And preventing viruses is something we're good at. Since Edward Jenner realised in 1776 that milkmaids appeared to be immune to cowpox, we have been able to prevent disease by injecting into the body a killed or weakened form of a virus to create an immune response. The immune system remembers the virus and is then able to fight it when it appears for real.

Straight after you have your shots, cells called B-lymphocytes detect the antigen (foreign substance) in the vaccine and react as if a real virus was invading your body. They multiply and form identical cells that can inactivate the antigens. After a while your body will stop making the antibodies, but memory B cells remain dormant.

It's been a huge success story. Smallpox has been eradicated from the face of the earth, with no new infections reported in humans since 1977 in Somalia. Measles and polio are almost eradicated, although infections are picking up again in some parts of the world where immunisation has dropped off. To avoid infection, you need to contain the virus. That means upping the hygiene and quarantining infected people. During the SARS outbreak in Hong Kong, almost everybody wore a face mask and washed their hands in viricide wash. The rate of infection for all viruses dropped by 80 percent.

So how do you ward off infection?

''Just follow the basic, sensible advice your mother gave you,'' recommends Collignon. ''Don't cough over everybody if you're sick, avoid being in close contact with other people . . . and wash your hands frequently.''

Adapted from Reader Digest