Prime Time Replay:

Christopher Wills
on the co-evolution of humans, diseases,
and disease resistance


MsgId: *breakthrough(1)
Date: Wed Dec 24 11:43:38 PST 1997
From: moderator At: 152.163.197.240

Hello, and welcome to Breakthrough Medicine. I'm your moderator, Madeleine Lebwohl, and at 12:00 noon I'll be speaking with Christopher Wills, a professor of biology at University of California, San Diego, and author of "Yellow Fever, Black Goddess." Please join us!
MsgId: *breakthrough(2)
Date: Wed Dec 24 11:54:26 PST 1997
From: Christopher_Wills At: 132.239.144.16

Hi
MsgId: *breakthrough(3)
Date: Wed Dec 24 11:56:58 PST 1997
From: moderator At: 152.163.197.240

Good to have you here. In your book you talk about the many forms of disease and our susceptibility, and how our genes protect us. Can we start by talking about the biggest problems you see on the disease front. This is now going to be an in-studio interview.

CW: There are several diseases that are either new or reemerging and that pose considerable dangers to many people in parts of the world that are afflicted by war, by overcrowding, lack of medical care and so on. Among these of course are tuberculosis, which is resurging throughout the world, Dengue fever, possibly Yellow Fever, and some of the new viruses, particularly the AIDS virus. All of these, and a number of others pose real problems.

But what I contend in my book, is that these dangerous diseases have their own vulnerabilities. If we keep our wits about us we should be able to find out what they are and home in on the weaknesses on these apparently indestructible organisms.

MsgId: *breakthrough(6)
Date: Wed Dec 24 12:05:22 PST 1997
From: moderator At: 152.163.197.240

When you identify a reemerging disease, is it always when people have started dying, or are they sometimes found when people are just getting sick -- how fast is the discovery process? Are people aware, in certain regions, to watch out for emerging pathogens?
MsgId: *breakthrough(7)
Date: Wed Dec 24 12:07:34 PST 1997
From: moderator At: 152.163.197.240

CW: Well that very much depends on circumstances. In a war situation, or a situation where refugees are crowded together, diseases may emerge very quickly. In the refugee camps of Rwanda, or the former country of Zaire, cholera and typhus appeared immediately. These people had no medical background and no ability to understand these diseases. In situations where more information is available, then people throughout the world are becoming more conscious of the diseases that afflict them.

The World Health Organization and many non-governmental organizations are making great strides in conquering scourges like polio, Guinea worm, and river blindness. None of which had been understood by the peoples who were afflicted by them. The important thing to remember, I think , is that no matter what the pathogen, our rapidly growing information about how cells work, is enabling us to attack them in new and very effective ways. The big problem comes with ignorance and the inability of both people and nations to face the consequence of their actions. Many countries in Africa, for example, refused to admit that AIDS was a problem until the disease had spread through a large part of the population.

MsgId: *breakthrough(9)
Date: Wed Dec 24 12:13:01 PST 1997
From: moderator At: 152.163.197.240

In your book you talk about how diseases can be present, but there can be resistant members of the population that don't catch them, and their presence protects the rest of the community. What exactly is that mechanism?
MsgId: *breakthrough(10)
Date: Wed Dec 24 12:15:16 PST 1997
From: moderator At: 152.163.197.240

CW: The mechanism is a very interesting one, and we have actually harnessed it in our attempt to control disease. It is called herd immunity. If you immunize 90% of the school age children against measles, then the measles virus can no longer spread because there are too few susceptible children in the population. The immunized majority protects the unimmunized minority. But if you let your guard down for a moment, as has happened, and the immunization rate drops below 90%, the virus which has been hiding somewhere, reappears and there is a measles outbreak.

The phenomenon may apply to naturally occuring immunity as well. There are members of every population who are more resistant to a particular disease than others are. Just recently its been discovered that there are high frequencies of resistance genes to the AIDS virus in both European and African populations. These genes are not common enough to confer complete immunity to the population, but if they were to become common, they would not have to spread through the entire population to confer immunity. The AIDS virus is difficult to transmit even between susceptible people, and if a large fraction of the population were resistant, then the virus would no longer be able to spread.

Now, this is unlikely to happen in the case of the AIDS virus, because it would require that most susceptible people die of the disease. But it may be happening on a smaller scale with many different diseases simoultaneously. As susceptible individuals increase in number in a population, or as the population becomes more crowded, genes that confer resistance to the disease will be locally selected for. Now, we don't know the extent to which this happens in the human population, but we've recently found evidence that it seems to be going on in two different tropical rain forests.

These forests, one in Panama and one in Malaysia, have many different species of trees, which is typical of most tropical forests. Ecologists have puzzled about why there should be so many species of trees, since this would imply that there are many different ecological niches in the rainforest. We have found that in both forests, there is a tendency for trees of a given species that are crowded together to reproduce poorly, while those that are less crowded reproduce more readily. Further, crowding itself has a negative effect. A pattern that you would expect if disease organisms of various kinds, were spreading through the forest, and could spread more easily in the crowded areas. We suspect that a herd immunity process is working in the rainforest as well. Whenever a given species becomes too common in a given area its diseases will begin to spread and it will not be able to reproduce readily. This pattern maintains the diversity of rainforests, and we suspect that it may maintain the diversity for resistant and susceptibility in the human species as well.

MsgId: *breakthrough(15)
Date: Wed Dec 24 12:26:24 PST 1997
From: moderator At: 152.163.197.240

When diseases that haven't been seen in a while suddenly reappear, what is the pattern that you're going to see?
MsgId: *breakthrough(16)
Date: Wed Dec 24 12:37:01 PST 1997
From: moderator At: 152.163.197.240

CW: Many diseases go short term cycles, and this has to do with the immunity of the population, and not directly with genetics. In the case of influenza, for example, the disease goes through cycles that are a function of whether people are immune to a particular strain of the virus, or to a strain that resembles it. But on the larger scale, there are many other diseases that have come and gone in the past for reasons that we do not understand.

For example, in Tudor England, a disease called the sweating sickness appeared and dissappeared over a couple of decades and to this day we have no idea what it was. Many other diseases have come and gone as a result of small changes in the way that people have lived. These changes are sometimes enough to break the cycle. In the seventeenth and eighteenth centuries, there was a dramatic dissapearance of the Black Death. And we have no idea why this happened, although we suspect that it must have been do to almost imperceptible improvements in public health during this period.

MsgId: *breakthrough(19)
Date: Wed Dec 24 12:40:40 PST 1997
From: moderator At: 152.163.197.240

Does that mean that people tried harder to get of the rats?
MsgId: *breakthrough(20)
Date: Wed Dec 24 12:43:10 PST 1997
From: moderator At: 152.163.197.240

CW: No, it wasn't as simple as that. People had no idea of the connection between rats, fleas and the plague. But it seems likely that improved ways of storing food, improvements in sanitation, and other unknown factors, must have contributed to the decline. Changes in the rat populations may have happened at the same time. Perhaps driven by these alterations in the environment. The point I want to make is that it is sometimes surprisingly easy to break the cycle of disease. And this brings me back to my first point, is that diseases are more vulnerable than we suspect.
MsgId: *breakthrough(21)
Date: Wed Dec 24 12:44:22 PST 1997
From: moderator At: 152.163.197.240

In our genetic makeup, you mention that there are signs of past encounters with viruses. How do you identify that?
MsgId: *breakthrough(22)
Date: Wed Dec 24 12:47:20 PST 1997
From: moderator At: 152.163.197.240

CW: There is a family of viruses, to which the AIDS virus belongs, that can insert their genes into our chromosomes. It turns out that our chromosomes are filled with the remains of ancient viruses that came to live there. These viral remains are now no longer active because over time they have accumulated so many mutations that their genes no longer function. But like ships trapped in the Sargasso Sea, these viruses bear witness to the many encounters that we must have had with them in the past. So far, the AIDS virus, while it can insert itself into the chromosomes of some of our cells, has not inserted itself into the cells that we pass onto the next generation, the eggs and the sperm. But it is obvious that many other AIDS like viruses have succeeded in doing so in the past.

We are the result of a long evolutionary warfare that has been carried out with many different pathogenic organisms, and that has to a great extent, made us what we are.

MsgId: *breakthrough(24)
Date: Wed Dec 24 12:52:51 PST 1997
From: moderator At: 152.163.197.240

How long does it seem to take for populations to get immune to diseases they are regularly exposed to? And do you think that malaria will ever reach a similar situation as chickenpox, where more people are immune?
MsgId: *breakthrough(25)
Date: Wed Dec 24 12:55:37 PST 1997
From: moderator At: 152.163.197.240

CW: In the short term, populations can acquire immunity against disease quite quickly, but they can also lose it. In the case of polio, populations in the 19th century were largely immune to the disease, because children almost all acquired it during early life. Polio gives a virtually harmless flu-like set of symptoms in an infant, or young child, but causes a terrible disease in a youth or adult. The spread of the disease, ironically, was halted by better public health, and the polio outbreaks in the middle of this century, were caused by the fact that people were exposed to polio later in life than they otherwise would have been.

In the longer term, diseases may cause such large changes in the makeup of the host population, while at the same time changing themselves, that they may become less virulent over time. This has not happened with malaria, but over a long period of time it may. We're talking here about centuries, or possibly even millennia, because we know that malaria has been virulent in our species for a long time. But if we look at the malarias that afflict our closest relatives, the chimpanzees, we see that they produce far milder symptoms. Chimpanzees have lived in an ecologically stable situation for a very long time, which may explain why their malarias have such mild effects. We are living in a time of ecological upheaval. And this has contributed to the virulence of many of our diseases. Human malaria is transmitted by mosquitoes that are not as well adapted to its transmission as the chimpanzee malaria mosquitoes appear to be.

The virulence of so many of our diseases can be traced to the fact that we have disturbed the natural world so much in our recent history. The strains of bacteria and viruses that are transmitted in our species at the present time may, as with the Black Death and malaria organisms, be rather poor at the transmission process. Even so, the fact that we are so crowded together and that our behaviors sometimes enhance this spread, has allowed these vicious pathogens to spread in spite of their own defects. The point I make in my book is that, if we keep our wits about us, we can keep these organisms at bay, but that ignorance and lack of political will, work against us. Pathogens are cunning enemies, but they are not infinitely cunning. We must be cunning in return.

MsgId: *breakthrough(31)
Date: Wed Dec 24 13:07:15 PST 1997
From: moderator At: 152.163.197.240

Thank you for joining me today.
MsgId: *breakthrough(32)
Date: Wed Dec 24 13:08:00 PST 1997
From: moderator At: 152.163.197.240

CW: Well, thanks very much for the opportunity. I hope to talk to you again. When the interface becomes a little friendlier.


Home || Prime Time || Live Science || Machine Dreams || Project Open Book || SF-Fantasy-Horror
Continuum || Antimatter || Mind-Brain Lab || Interactive IQ || Gallery || OMNI Toons

Questions, comments and suggestions can be mailed to the webmaster.


Copyright © 1998 by Omni Publications International, Ltd. All Rights Reserved.