After I debunked my own bit of speculation about why pandemic flu viruses seem to have an earlier first wave, I have been worried that I have left the speculation community with less speculation to enjoy. So I have been hard at work drumming up some new speculation for the enjoyment of the various speculation mongers out their.
I have been told that (regardless of the mechanism of the cytokine storm) viruses which cause the more lethal infections are ones which are adapted to be able to enter the cells in the lower respiratory tract. the avian flu (H5N1) does this, which is why it has such a high death rate but it is not adapted to the upper respiratory tract where one victim can easily form aerosols which can be easily transmitted to the upper respiratory tract of a new host. The adaptation to the upper respiratory tract is the big event epidemiologists are dreading for bird flu but since it kills so many people it does not have a lot of time to make the get the on-the-job-training in the upper respiratory tract of humans. So in the short-term, probability is on our side.
The swine or H1N1, however, may be already adapted to the upper respiratory tract but not so much to the lower tract. That makes it a good traveler, especially since it is novel to humans but it is largely a mild killer.
Let’s assume for the moment that this is how most pandemic flu viruses start off. As it spreads around the world it gets to spend a lot of time in humans and some strains start to adapt to being able to enter the cells of both the upper and the lower respiratory tract – a much more likely event given the amount of time the virus is able to spend in humans since it does not kill them. Now you have a disease which causes the aerosols needed for easy transmission being created in the upper tract and more irritation which causes coughing contributing to transmission as well. So a more lethal and more transmissible virus is born and begins what we notice as the second wave.
I am really not rooting for a lethal pandemic. But I can’t help but feel that we have been on rather a lucky streak as far as air born pandemics are concerned. Even drug resistant TB doesn’t sweep through cities the way the pneumonic plague can and we really dodged a bullet with SARS. 1918 seems so long ago but my grandmother was a survivor of it. Our high populations and dense cities; our rapid international travel and many environments from slums to skyscrapers make me confident that their will come a day when a global pandemic begins disrupting our societies the way it did in 1918. And if you might be dreaming about how nice it would be to be the last human on earth wandering through the cities with zoo animals for company like in the movie Twelve Monkeys, forget it. A small fraction of people will die. Just enough to disrupt our health care and cause labour shortages and mass absenteeism to wreak havoc with our economies. And was it really necessary to show Bruce Willis’ butt in that Twelve Monkeys movie? I really could have done without that.