Depending on your perspective, viruses are the most primitive organisms on the earth, or the most single-minded. They are nothing more than nano-sized gene replicators: they possess just enough genetic instructions to create a copy of themselves, and are dependent on the machinery inside the cells of their hosts to do even that. And trillions of viruses never even get the chance. They lie exposed in the environment for days or weeks, never interacting with the types of cells they can infect (and possessing no ability to seek out those cells themselves) until they finally fall apart.  But those few virus particles which happen upon the right host cell (and the even smaller number which finally make it inside) are perfectly adapted to borrow the chemical factories of the host cell to make copy after copy of themselves, until they finally exhaust their host and burst forth to find thousands of additional cells to infect.

Fortunately, even then they may be of little consequence to the infected animal. In the case of cold viruses, for example, the only evidence we have for being infected is the inflammatory response our own bodies create to kill the virus particles. The cough and runny nose and fever and diarrhea are all the product of our immune response, not the effects of the virus. And within a few days, the virus particles are wiped out, while the number of killed host cells is trivial by comparison.

 Occasionally, though, a virus can be, well, virulent, which means it can cause a dangerous amount of bodily damage, either by direct injury to far too many host cells (as is the case with HIV viruses and CD4 white blood cells) or by generating a vicious immune response, one in which the immune armies in our bodies “go nuclear” and leave widespread destruction in their wakes. The influenza viruses have that potential. They are particularly adept at infecting the cells lining our respiratory tracts, killing off great numbers of those cells, and triggering an immune response which floods the area with the body’s defense mechanisms. Unfortunately, “flooding” is not a good thing in the respiratory system. In addition to the simple oxygen depletion that results from filling the lungs with fluid, it provides a great breeding ground for bacteria, and a secondary bacterial pneumonia, often the actual killer in a killer flu outbreak, results.

 Influenza viruses are composed of just eight genes. Two of them create bristle-like particles on the surface of the virus. These bristles, the hemagglutinin (H) proteins and the neuraminidase (N) proteins, are the focus of much attention, as they are responsible both for how flu viruses get into our cells, and for why they seem to get past our immune system year after year.

 Flu viruses, it turns out, do a particularly poor job of making copies of their proteins, during the time they are hijacking the host cells’ machinery. Their gene copying proteins are perhaps a million times more careless than our own copying proteins. (For those seeking evidence of evolution occurring right in front of us, here it is, but that’s another discussion.) The result is sloppily built H and N proteins. No doubt many of these H and N proteins don’t even work. But the flu virus creates millions of copies of itself, and so a handful of broken copies are meaningless. However, the sloppy H and N proteins are not recognized by our immune system, which is a finely honed machine, and is designed to look for precisely the same H and N proteins it encountered in previous flu infections. As flu infections ripple around the globe, the H and N proteins slowly change, until by the time the virus returns to us a year later it is different enough that our immunity from last year’s infection (either from a vaccination, or because we had the flu) is insufficient to keep us from being susceptible to infection again.

 Actually, that’s a bit simplistic. The H and N proteins don’t change all that much, and so most years there are enough of us with enough immunity to prevent the virus from getting much of a toehold, and those that become infected suffer a relatively minor (if miserable) illness. But there are several subtypes of each H protein gene and N protein gene. When the world sees a new widespread flu outbreak, it usually means that an H protein subtype and an N protein subtype have somehow combined to make a flu virus much different than has been seen before. The new virus may be particularly good at infecting cells. If, on top of that, the collective immune systems of the world’s population don’t recognize any part of the new virus, the stage is set for a devastating sweep of infection around the globe: a pandemic. In the past, this sweep would take months, as the virus traveled from person to person. But with widespread air travel, infected individuals can spread out all over the globe in the three or four days it takes for them to experience flu symptoms. Like cinders from a wildfire, these individuals will start new outbreaks wherever they land, and the infection can spread world-wide in a matter of weeks.

 I’ve already heard infectious disease specialists rolling their verbal eyes as they speak on the radio about the so called “swine flu.”  Pigs, along with horses, birds, and humans, are among the animals most susceptible to influenza viruses. Each species tends to suffer from its own particular flu variety for a few years. But then an H protein gene seen most recently in pigs may somehow match up with a human strain N protein, and a new influenza virus is born. The specialists much prefer referring to these strains by their H and N designation, rather than by calling them “swine flu” or “bird flu.”  In truth, though they may have their origins in swine or bird viruses, they are something new. The present potential pandemic is officially referred to as the 2009 H1N1 virus. By 2010 hopefully it will have mutated, and there will be sufficient worldwide immunity to make it much less threatening. But for now the risk is great, and the fight is on.  Meanwhile, you cannot catch the virus from pork, even if the pig itself had the flu. That won’t stop the widespread ban on meat exports, as China has already announced against pork from Mexico and some U.S. states. (What goes around comes around, as China had to destroy millions of chickens in the “bird flu” (H5N1) outbreak of 1997.)

 What you can do is wash your hands. Influenza viruses are broken apart by detergents; simple as that. They are also susceptible to deactivation by alcohol, so the use of hand sanitizers can be very beneficial, especially in public places such as airports and hospitals. Flu infections are not affected by antibiotics, so getting an antibiotic prescription from your doctor at the first sign of symptoms will not lessen the severity of the illness. However, antibiotics are life-saving in individuals who develop pneumonia after catching the flu, so someone with severe symptoms should see a doctor quickly. Get vaccinated if and when a vaccine becomes available. In addition to at least lessening the severity of your symptoms, your immunity reduces the number of places the virus can hide and replicate.

 The world waits to see how virulent this particular flu will be. If it is particularly severe (say, leading to the hospitalization of 1% of the U.S. population), it could easily overwhelm our existing health care resources. The hospitals in my city admit roughly 5000 people per month. If 1% of the population required admission for flu complications within, say, a three month window, the number of monthly admissions would double.

On the other hand, if most of us escape unscathed, it will be interesting to see what our collective response will be. Will we dismiss our health institutes as doomsayers and mock their containment efforts? Or will we recognize for once that preventive medicine and an abundance of caution actually saved our butts? We shall see.