Saturday, May 9, 2009

Swine Flu Over The Cuckoo's Nest

We have been TOLD by several authorities that it ISN'T the SWINE flu.

Despite the tendency of pigs to get a strain of influenza that is genetically similar to this particular strain, we are going to call it ( as we really should have anyway) "Influenza A: H1N1". Not nearly apocalyptic enough for a good media footprint, but scientifically accurate.

And it isn't the "Mexican flu", either, thank God, even though across Latin America people of Mexican origin are being refused service in restaurants and refused rides in taxis. Solidaridad por siempre!

Well....the truth is, it shouldn't REALLY be INFLUENZA, either. The "scientists" of the Reformation (God bless 'em, operating on what training and what little information they had) decided that the epidemiology of the disease matched the passing of the seasons, so the sickness must be due to the influence ("influenza" in the dialect of old Florence) of the stars.

OK, so it was the BEGINNING of an appreciation for the origin of the disease, and after a thousand years of use, the word has taken on a different meaning. Another disease name, malaria, literally means "bad air disease", since people postulated that Spring-time swamp-gas emissions were causing the symptoms. Closing your windows at night seemed to reduce the incidence of the disease so obviously if one did not breathe the bad night air ("malaria")one was more-or-less protected. The strategy sort of worked because closing the windows kept out the mosquitoes that carry the plasmodium of malaria. It they had tried using screens on the windows, they would have seen that the gas, which could penetrated the screens, was not at fault. At the time, people did not correlate bug bites with systemic sickness.

Back to "the flu".

Influenza follows a seasonal pattern because it incubates in populations of migratory birds. On their way north, they encounter bodies of water contaminated with human sewage and pick up viruses that are shed in human poop. These viruses gradually spread through the bird population, killing some, sickening others and mildly inconveniencing most. Most importantly, the virus mutates and stabilizes under physiochemical pressure from the new host population.

(The virus doesn't do this on purpose; it's just that the really virulent mutants kill their hosts before they can be transmitted to new hosts, and the moderately virulent viruses make their hosts too sick to interact significantly with new hosts. It's a mathematical thing. The virus "adapts" to the new population by selecting for the mutants that keep their hosts moderately healthy, even at the peak of viremia)

When the birds fly south in the Fall (or Spring, if you are south of the Equator), they again encounter human poop, picking up another form of the virus, but the birds also poop in the same bodies of water thus passing their modified virus to the human population. Pigs and people exposed to the contaminated water acquire the virus and pass it on to other people by coughing, sneezing and sharing saliva.

In parts of the world where people and pigs live in blessed harmony together, there is a magnification factor: pigs, once infected, become "virus factories". Any respiratory virus in pigs is exhaled in astonishing numbers. Flu viruses don't live long in the open air. We are usually infected by transferring virus to ourselves by rubbing the virus into our eyes, picking our noses or eating with unwashed hands. Occasionally we will pick it up directly from the air, but the flu is spread by "large droplet transmission". The droplets are large enough that gravity sorts them out of the ambient air. If you sneeze or cough into your sleeve, the viruses are trapped in the fabric, where they will quickly dry out and die. Pigs, having no sleeves into which to sneeze, spread these viruses into the air and onto nearby objects where people encounter them.

"Small droplet transmission" diseases, such as "foot and mouth disease" in animals, are spread by wafting of the droplets on air currents, so the droplets are very small, indeed by comparison. There was one case where hardy viruses were wafted in small droplets across the English Channel! (We think this is what happened: no-one wants to admit rowing across the Channel with a diseased pig.)

(Generalizations are dangerous: SARS which terrified the world briefly in 2007 and nearly ruined Toronto tourism, is usually a "large droplet transmission" disease. In the hospital, though, once the patient is hooked up to a respirator, it is spread as a "small droplet disease", being aerosolized by the high-pressure air from the respirator and thence into the air-conditioning.)

It turns out that Influenza A (H1N1) 2009 is less virulent than was expected. The initial panic derives from the resemblance of this bug to the one that killed as many as 50 million people in 1918. That one was dangerous because it somehow tricked the immune system of the patient into attacking the patient's own tissue with a biochemical disaster called a "cytokine cascade". In the lungs, that is a Bad Thing. Death by pneumonia was VERY quick. Out of the tens of thousands of recent cases in Mexico, there have been a few tens of deaths attributable to the "cytokine cascade" phenomenon. For the most part, even our unfortunate friends to the south have at most been miserably sick and many of them not sick enough to stay home from work (thus spreading the virus more efficiently!).

Even if the 1918 virus was released on today's population, it is unlikely that the death count would be as high. The world was thinly populated by comparison in 1918, and there were vast numbers of folk who had never been more than 50 miles from their house. The "herd immunity" of humanity to that particular virus was very low. In 2009, the population density is such that your probability of encountering influenza virus during any year is pretty close to "1". We may not have been exposed to THIS particular mutant, but we have seen its brother or first cousin. Our immune system is primed. We are like a community who, having bought encyclopedias from one travelling salesman, are unlikely to be conned into buying a marching band from the next one.

Rational thought doesn't prevent bureaucrats, politicians and media flacks from trying to build careers on public anxieties. The World Health Organization (WHO?) declared that Influenza A (H1N1) was a "pandemic", a disease outbreak of global proportion and importance. The mildness of the outbreak has people asking whether WHO actually has any value in the preparation of the world for plagues and pestilence, to which WHO reponds "well, the influenza of 1918 began as a mild respiratory syndrome, then returned five months later as the most virulent pandemic in recorded history". I am reminded of millemialists who, on the deadline of the End of the World having passed without incident, recalibrate using a different calender and say, "well, the world will REALLY end in 18 months...oogabooga....".

Meanwhile, books, and TV programs, and potentially a feature film, flood the public with dire warnings and misinformation. Should the Real Thing come along in this generation we'll be sitting ducks, having had our "danger antennas" worn down to nubs by constant bombardment. "Flu-ga booga", we call it.

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