Thursday, 03 March 2005

Viruses: These things that invade our bodies

For the past fortnight I have been knocked out by chickenpox. Our two youngest daughters brought the virus home from school about five weeks ago. I had no idea adults could catch what is widely regarded as a kindergarten illness until a visit to my doctor confirmed that my increasingly severe chills and headaches (along with a couple of ugly tell-tale rashes on my chest) were the first signs of an attack.

The leaflet handed to me informed "Symptoms are usually more severe in adults than in children" and warned, "You can expect to have a few uncomfortable days." This turned out to be an understatement. At times I felt I was at death's door; a sentiment clearly shared by my anxiously watching family as I progressively disappeared under a blanket of huge spots, lost all appetite and suffered sleepless nights and listless days. My poor angels had several bitter fights over just who "gave daddy chickenpox".

Chickenpox is caused by the varicella-zoster virus, a member of the herpes family. Our immune system responds during an attack by producing antibodies that should provide lifelong immunity thereafter, although the condition can re-emerge as shingles in later life. For this reason, doctors will not prescribe antiviral treatment unless there is an ancillary life-threatening condition in exceptionally vulnerable patients. My advice to anyone unlucky enough not to have had a mild attack in childhood (10% of the adult population) is to avoid infected people like the plague. If you live in the USA you can get a vaccination -- a pre-emptive strike not favoured by authorities on this side of the Atlantic.

Confinement to bed has given me plenty of time to watch the news on TV. My misery was compounded by repeated warnings that we could be hit anytime now by a pandemic of bird flu (avian influenza). World Health Organisation officials are worried that this so far incurable affliction that has already spread through human-human contact may soon combine with a human flu virus to create a new strain that will sweep continents. The result will be a catastrophe of biblical proportions.

What exactly are biological viruses? A virus is made up of a DNA or RNA genome surrounded by a protein coat. It is far from anything that we would consider a living cell or microorganism. A virus particle can only reproduce by invading and taking over the cells of 'host' organisms since it completely lacks the cellular machinery for self-reproduction or independent metabolism. Thus, the argument runs that viruses are not 'living' things. But because they are complex assemblies of molecules that exhibit genetic inheritance, some scientists view viruses as a kind of artificial life that fall somewhere between living and non-living things. Viruses make excellent Trojan horses for the introduction of DNA into cells by geneticists researching gene therapies for human diseases. However there is a high risk of viral infection (deaths have occurred in some trials) so work in this area is tentative and cautious.

Where do viruses come from? This is still a mystery to science. The most widely held belief is that viruses actually originated from their preferred host organisms at some point in the distant past. Suspect sources are plasmids (circular double stranded DNA molecules that are separate from chromosomal DNA) and transposons (sequences of DNA that can move around to different positions within the genome of a cell, sometimes causing mutations). But why should genetic particles that originated from an organism cause such havoc (indeed death in most cases) when they re-enter the organism? It has also been suggested that viruses could be extremely reduced microbes, that they may have appeared separately in the primordial soup that gave rise to the first living cells, and that the different sorts of known viruses probably arose through different mechanisms.

Viruses are a frightening conundrum for humans. A non-living particle invades a living organism without warning or invitation, springs to life, reproduces in vast numbers, and then either lies dormant or exits to its previous inanimate state in the environment. While in the organism it may mutate by re-arranging its genetic coding but we do not know what the signal might be for such mutation. From time to time it also jumps host (e.g. from bird to human). All this makes it extremely difficult to eradicate or counter viruses. Only vaccinations (deliberate infusion of a mild form of the virus to stimulate production of antibodies by our immune system) offer any sort of protection. Coming up with a vaccine that works, can be safely introduced into the life chain and is relatively easy to mass-produce is a tedious, expensive and laborious process that usually requires many years of research.

Meanwhile we all live under the shadow of unpredictable natural pandemics, the threat of new lab-produced viruses for biological warfare and deliberate dissemination by terrorists.

C'est la vie.