lessons from 1918 and speculation on bird flu

To us as individuals, of course, it doesn't -- we don't control the course of a virus' evolution.

But Ewald does discuss the 1918 flu virus. According to him, that virus was so exceptionally deadly because it evolved in the trenches of Europe during World War I.

And not really for the obvious reasons that the men were hungry and stressed out due to the war -- but because soldiers sick with the flu still came into contact with many other soldiers.

They lay in trenches close to all other soldiers. Until transported out in an overcrowded truck or train car. To an overcrowded hospital room.

Therefore, that influenza virus was rewarded for evolving into a hugely virulent disease. Although it sickened thousands of soldiers, they could not retreat to a bed away from everybody but immediate family. They were kept in close contact with healthy soldiers, wounded soldiers and soldiers sick with other diseases.

We are not in a world war situation now. So does that mean that bird flu will not remain as high fatal as it is now (over 50% of its human victims have died so far)?

Nobody knows for sure.

But I believe that there's another factor at stake.

Maybe the 1918 flu virus evolved into a highly virulent strain in the trenches of war-torn Europe -- but it still spread around the world to many places at peace. From Spain (which was unjustly accused of causing the disease) to remote Arctic Eskimo villages and remote south Pacific islands.

However, many cities in the developing countries of Latin America, Africa and Asia are extremely dense and crowded. Most of you reading this have no idea how many people can live in a maze of corrugated iron, broken glass and rusty wire. I have seen such neighborhoods, and they are incredibly poor -- yet home to millions of people.

If bird flu spreads into the poor neighborhoods of the dense mega-cities, it will find many victims.

My guess is, that when people in such areas start catching a contagious form of bird flu, they will not seek medical treatment, because they can't afford it. They will lie down at home -- which means being in close contact not only with the family members they live with, but all the neighbors who stop in and visit. They do not have separate bedrooms or even beds. So they will just have to lay in a corner and struggle for breath.

The people most likely to be taken for treatment are children, who are particularly vulnerable and the ones most parents will want to treat. They are also the people who can spread the virus most easily. So it will then spread to the clinics.

Once the pandemic is widespread and known, the local government may be organized enough to attempt to pick up all the cases and isolate them. So bird flu patients will be taken away in trucks and sent to overcrowded hospitals.

Many governments will be overwhelmed by the situation and may not even be organized enough to collect the dead bodies. Then the sick and the dead will continue to infect the general population.

Though at some point many of those people may well flee to rural areas or at least avoid anybody who seems sick.

I'm not up on the location of all bird flu victims to date. The only ones I know of that were city residents, were in Hong Kong, a relatively wealthy city. Other bird flu victims seem to have lived in rural areas where they come into contact with lots of chickens.

Therefore, I must conclude that although it hasn't happened yet, evolutionary biology does not rule out the evolution of a highly virulent strain of contagious bird flu. Even though we don't have a world war going on in Europe.

review of Evolution of Infectious Disease by Paul Ewald

Evolution of Infectious Disease by Paul W. Ewald came out in 1994 and is still a highly interesting and maybe revolutionary technical foundation behind evolutionary biology or evolutionary epidemiology.

I wrote about that somewhat in my earlier review of his later book, Plague Time. But somehow I'd forgotten that the same book and author presented both fundamental ideas that:

1. What we call chronic diseases such as heart disease, cancer etc are caused by infectious agents.

2. Infectious microorganisms change through evolution and we can use that to control their effect on us.

The fundamental concept of this book is to point out that microorganisms evolve just like we all do -- and they evolve in ways that increase their opportunity to increase and multiply.

This seems fairly simple, even obvious, but I know I'd never thought about it before. I've always assumed that a cold germ was a cold germ was a cold germ. It never occurred me to that germs do change over time -- and since many microorganisms multiply so quickly, the changes are easily observable by people, over years if not months.

He takes a lot of time to discover the concept in biology that parasites and hosts always co-evolve to form a beneficial relationship rather than a hostile one.

He points out that this is true only when it's in the best evolutionary interests of the parasite to do so.

In cases where rapidly killing the host will help the parasite spread faster -- guess what, it kills the host quickly.

Thus, the rhinovirus that causes the common cold is relatively benign (that is, non-life threatening even though irritating) virus to people. That is because is spreads through the air by coughs and sneezes and via hands holding objects.

Thus, the rhinovirus can spread to more people if its infected victims feels well enough to go to work, shopping etc -- where they cough and sneeze and spread the cold germs to the rest of us.

If a cold made us feel so sick to death that we had to stay in bed, we would come into contact with only our close families and therefore the virus is rewarded for not killing us, by spreading to more people.

Some viruses spread more easily by making people so sick they stay in bed -- such as malaria. That's because it's spread by mosquitoes, not in person contact. A sick person lying in bed is even more at risk of being bitten by mosquitoes, who then carry the virus to more victims.

Where does AIDS fit in?

HIV is a virus that spreads primarily through sexual contact. Therefore, it is to HIV's advantage to lie low and not cause great illness for many years, to increase the victim's chances of spreading HIV to their sexual partners.

If HIV immediately caused grave illness and opportunistic infections, it could not spread much -- because people with full-blown AIDS are too sick to have much sex and even if they still want to, they're too obviously sick to attract many sexual partners.

Ewald argues convincingly that HIV could be strongly encouraged to evolve to a more benign virus by minimizing the number of sexual partners people have. He backs this up with statistics from Africa, where the regions with social disruption and where people have many sexual partners have a high percentage of the virulent HIV-1. Regions of Africa with social stability and where people are discouraged from sexual promiscuity tend to have HIV-2, which is much less dangerous.

The logic here is that, the more sexual partners an HIV-infected person has, the greater the chance HIV has of spreading to someone new in a relatively short time. Therefore, HIV is better off spreading more quickly and killing its host fasters, when they're have many sexual partners.

How might this apply today to bird flu? I'll discus that in a separate entry.