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Virus X: Tracking the new killer plagues

By rusty in News
Sun Jun 11, 2000 at 03:45:39 AM EST
Tags: Books (all tags)
Books

Consider, if you will, the following description:

As the illness progressed, and particularly in the most severely ill, there was a vivid rash that tended to coalesce into a livid reddening of skin over the face, trunk, and extremities. After the sixteenth day, the patients' skin peeled off, their hair fell out, and they lost their nails. Seven of the infected people suffered from severe hemorrhages from the nose, from the gums, and from the sites where blood had been drawn from veins...
Sound like something from the middle ages? Not at all. This is a description of some of the symptoms observed at the first known outbreak of the Marburg virus, in Germany, in 1967. And the symptoms only got worse from there.

With many doctors and public health officials in the 1960s and 70s proudly proclaiming that the fight against infectious disease had been all but won, ominous signs to the contrary were already rearing their ugly heads. The fears of naysayers would prove all too correct in the following decades, with epidemics and pandemics of new illnesses, such as Ebola, Marburg, AIDS, and the various Hantaviruses, and even the resurgence of diseases thought long-conquered, like cholera, dengue, and even plague.

Jack Ryan's 1997 book Virus X: Tracking the new killer plagues engagingly describes many of the biggest current threats to global human health, and provides a startling and compelling theory of the ecological causes of the new plagues.


I tend to read a lot of scientific books, and usually they're enlightening, often fascinating, but all too frequently the prose leaves something to be desired. The author who can bring a very specialized field alive for the non-specialist is truly one to be savored, hence this review. Ryan's writing, when he describes the investigative process of discovering and isolating a new virus is sharp, well paced, and as engaging as the best detective fiction.

My other frequent gripe with scientific books for the non-scientist is their treatment of the technical details. Often scientific authors are forced to employ a very specialized vocabulary, at which point they generally either carefully gloss every term for the layman, dragging the narrative into swamps of background, or they neglect to explain anything at all, leaving us wandering in a wasteland of latinate mystery. Sometimes they choose the other extreme and avoid technical details at all cost, leaving the intelligent non-specialist feeling like they don't know any more about the topic than they did when they started.

Ryan again manages to thread this needle, employing just as much technical terminology as he needs to, and explaining some of the more complex processes, such as the genetic manipulations needed to clone samples of viruses, without either talking down to the reader, or assuming that his audience is composed entirely of PhD.s.

But enough of that. The real meat of this book is two fold. First, it is an enlightening primer on the current (as of 1997) state of global epidemiology, and an overview of the biggest current threats to public health, especially in virology. Ryan describes the first outbreaks of such emerging viruses as the sin nombre Hantavirus in the Southwestern US, Ebola Zaire in Africa, and HIV, in Africa and the US. He follows epidemiologists as they attempt to determine the causes of mystery disease outbreaks, isolate the viruses responsible, and discover the virus's natural reservoir in the local ecology. For anyone who enjoyed The Hot Zone, the real life stories presented here, are even more interesting.

Finally, Ryan presents his theory on where these brand-new viruses are coming from, and why they are often so disastrously fatal to humans. The "standard theory" is that since we know that there are viruses specific to nearly every species of life on earth, and we know viruses often mutate very rapidly, sometimes a virus from one species will happen to mutate in such a way as to be infectious, and even fatal to another species, such as humans.

But Ryan's theory is much more interesting, and, from the point of view of a confessed non-biologist, much more probable.

He tells the story of a certain type of ant, which builds its nests only around the base of a species of rattan cane that grows in Borneo. The ant colonies derive their sustenance from the sap of the cane, and in return, they will attack and sting any animal that attempts to eat their home plant. This is a classic example of symbiosis, where two different species evolve into a relationship where the behaviors of one perfectly complement the behaviors of the other.

Ryan postulates that viruses might be engaged in very much the same practice, at the level of the genome. Viruses are extremely dependent on their host species, since they cannot reproduce without using the genetic and biological machinery of the host. Most species harbor many strains of virus which infect them endemically, but do little or no harm to their host. The most common pattern in emerging virus epidemics is that of a virus from a local species suddenly "jumping" from it's natural host into humans, and proving to be disastrously fatal once past human immunological defenses.

This is the quandary: why would viruses select for aggressive lethality, when they themselves can't survive without a host organism? Many scientists dismiss it as chance mutation, but Ryan suggests that perhaps it's necessary to look at the bigger picture to understand this pattern. What if the virus isn't trying to establish a new host territory, but instead, is trying to remove a threat to its existing host species?

Another common pattern, seen for example in the first outbreaks of the sin nombre Hantavirus, is that viral epidemics are preceded by an unusual increase in the local population of their native "reservoir" species. Perhaps, argues Ryan, with the increased competition for resources between a virus's host species and another local species, the virus is acting as a defense mechanism for its current host, selecting for lethality to wipe out the competition, and preserve it's existing host species.

Obviously, he doesn't wish to ascribe intentionality to a virus. Clearly they don't "think" or "plan" to do this. But the effect is the same, since their behavior will likely be selected by maximum benefit to the species. Hence, Ryan neatly unifies both the symbiotic and the evolutionary strains of ecological thought, in a kind of evolutionary symbiosis between virus and host.

Along with this theory, Ryan proposes that humanity is going to have to start taking a much more holistic view of what our actions are doing to the world as a whole. Often, it seems, we are our own worst enemies, provoking new plague outbreaks by encroaching upon long-pristine territory. He feels that, if we continue upon our current course of deforestation and general exploitation of resources, it is only a matter of time before one of the emerging viruses combines both the dreadful infectiousness and lethality of, say, Ebola, with the efficient infective vector of the flu. An Ebola spread by airborne aerosol would be likely the worst disaster humanity has ever experienced, killing potentially 90% of humanity worldwide.

How can we avoid this doomsday scenario, this "Virus X"? Ryan argues convincingly that we must learn more about how viruses work, we must improve our preparedness for emerging pandemics, and most of all, that we must stop the pell-mell environmental exploitation that has been the hallmark of humanity since the industrial revolution, and before.

Overall, this was one of the best scientific books I have read in a long while, and it is highly recommended to anyone who'd like to learn more about virology, or epidemiology, or anyone who just likes a cracking good science yarn.

Virus X: Tracking the new killer plagues is 382 pages, plus footnotes and index.
It is published by Back Bay Books, and is available from Amazon.com and Fatbrain.com.
ISBN: 0-316-76306-3

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Virus X: Tracking the new killer plagues | 36 comments (36 topical, editorial, 0 hidden)
An exemplary review. At first it so... (none / 0) (#2)
by raph on Sat Jun 10, 2000 at 10:43:19 PM EST

raph voted 1 on this story.

An exemplary review. At first it sounded like it might be sensationalism, but in fact it is intellectually provocative, well written, and with just the right level of detail.

Viruses have nothing to do with me.... (3.00 / 2) (#4)
by Velian on Sat Jun 10, 2000 at 10:44:11 PM EST

Velian voted -1 on this story.

Viruses have nothing to do with me. :) Puuurdy easy to avoid 'em...

??? (none / 0) (#22)
by rusty on Sun Jun 11, 2000 at 03:57:28 PM EST

You live in a Biosafety Level 4 facility? 'Cause that's the only way you're gonna avoid them...

____
Not the real rusty
[ Parent ]
Rusty, I like the general idea, but... (none / 0) (#10)
by nuntius on Sat Jun 10, 2000 at 11:16:45 PM EST

nuntius voted -1 on this story.

Rusty, I like the general idea, but trim your post and then resubmit. We don't need to know great details about why you liked it, we want to know what its about so we can like it.

Be briefer; I had a hard time reading your descrip through.

Recommendations:

  1. kill the 3 paragraphs starting with "I tend to..."
  2. kill the 2 paragraphs starting with "Another common pattern..."
  3. resubmit
Otherwise a very good review!

Woohoo. I used to be obsessed with... (none / 0) (#3)
by fluffy grue on Sat Jun 10, 2000 at 11:18:55 PM EST

fluffy grue voted 1 on this story.

Woohoo. I used to be obsessed with these diseases. It's like I'm an alienated college Freshman all over again! ;)
--
"Is not a quine" is not a quine.
I have a master's degree in science!

[ Hug Your Trikuare ]

A very novel argument ... (none / 0) (#9)
by General_Corto on Sat Jun 10, 2000 at 11:24:22 PM EST

General_Corto voted 1 on this story.

A very novel argument Maybe there's something to being a tree-hugger after all! :)


I'm spying on... you!

Nice review.... (none / 0) (#8)
by Dr. Zowie on Sat Jun 10, 2000 at 11:38:58 PM EST

Dr. Zowie voted 1 on this story.

Nice review.

I don't know if I buy the thesis, b... (none / 0) (#6)
by magney on Sun Jun 11, 2000 at 12:00:34 AM EST

magney voted 1 on this story.

I don't know if I buy the thesis, but that's a helluva write-up.

Do I look like I speak for my employer?

We'll survive. But you're getting a... (none / 0) (#1)
by fvw on Sun Jun 11, 2000 at 12:27:27 AM EST

fvw voted 1 on this story.

We'll survive. But you're getting a +1 because of the nice long writeup :-)

Freaky freaky stuff man. But you a... (none / 0) (#5)
by Neuromancer on Sun Jun 11, 2000 at 01:06:03 AM EST

Neuromancer voted 1 on this story.

Freaky freaky stuff man. But you already knew that I thought that.

... (none / 0) (#7)
by slycer on Sun Jun 11, 2000 at 02:07:26 AM EST

slycer voted 1 on this story.



The idea of environmental exploitat... (4.50 / 2) (#11)
by mcelrath on Sun Jun 11, 2000 at 03:35:43 AM EST

mcelrath voted 1 on this story.

The idea of environmental exploitation being "bad" and introduction of virii into the population as "bad" seem to be orthogonal concepts. How does environmental exploitation have anything at all to do with virus transmissivity? Are new virii commonly found in lumber yard workers? Strip mine workers? I highly doubt it. An inter-species jump would come from inter-species contact. One would think that activities like camping, hiking, hunting, keeping exotic pets, and eating exotic animals would be prime candidates for inter-species virus transmission.

His expertise with virii not withstanding, it sounds like the author has an agenda.
1^2=1; (-1)^2=1; 1^2=(-1)^2; 1=-1; 2=0; 1=0.

Re: The idea of environmental exploitat... (5.00 / 1) (#20)
by rusty on Sun Jun 11, 2000 at 03:55:40 PM EST

(Note: See this comment for a hopefully clearer explanation of the mechanics of the theory)

The clear majority (something like 80%) of emerging viruses are coming from rain forest areas. There's a map in the book with points representing outbreaks of new, previously unknown infectious agents since the 1950's, and they are massively clustered in a belt around the equator. His point is that 2/3 of all species on earth live in the rain forest, and our wholesale invasion of the rain forest is bringing us into contact with many new species, which potentially harbor very serious infections.

New viruses are in fact usually found first in people who have been involved in invading a new habitat. There are exceptions, but often there is a strong chain of causality from a new human behavior straight to a population explosion in a previously harmless species, and a new infectious agent jumping from that species into humans.

One of the more convoluted examples is the outbreak of sin nombre hantavirus in the Southwestern US. The virus's natural reservoir is a species of mouse, which is common pretty much worldwide. There is good evidence that this mouse and humanity have lived together more or less since the "dawn of time". In Arizona, New Mexico, and Utah in 1993, there was a sudden explosion in the population of these mice, something like a 5-fold increase from normal. There had been a mild winter, and a wet spring, leading to a very large surplus of food, and making it easy for the mouse population to boom. The booming mouse population led to much closer contact between humans and mice than would be normal, with mice living right inside the homes of people, and of course, shedding virus wherever they went. Normally the mice did not live indoors, preferring to live in the open land surrounding towns. The first known outbreak of the virus occurred after a spring cleaning, which stirred up large enough quantities of dormant virus from mouse nests to infect some local humans.

So why did the mouse population boom? The weather, mostly. Why was the weather unusual? It was an El Nino year, in 1993, with warm water in the Pacific altering the normal weather pattern for the region. And why has there been so much of this El Nino lately? There is very strong evidence that links it to a global warming trend, and excess CO2 in the atmosphere. Put there, of course, by humans.

This is the general point-- that we need to seriously consider what our actions are doing to our habitat, and the repercussions of our behavior are not always particularly obvious.

The author does have an agenda, which is that human behavior is basically the worst threat to us now, as a species. The more we blithely ignore the interconnection of all life, the more chances we give ourselves to wipe ourselves out. Our patterns of environmental rape are only "bad" if you wish humanity as a species to continue to exist. :-)

____
Not the real rusty
[ Parent ]

Re: The idea of environmental exploitat... (3.00 / 1) (#26)
by sec on Sun Jun 11, 2000 at 06:10:21 PM EST

So why did the mouse population boom? The weather, mostly. Why was the weather unusual? It was an El Nino year, in 1993, with warm water in the Pacific altering the normal weather pattern for the region. And why has there been so much of this El Nino lately? There is very strong evidence that links it to a global warming trend, and excess CO2 in the atmosphere. Put there, of course, by humans.

On the contrary, there's some pretty strong evidence that 'global warming' is bunk. Check out this page for the case against global warming. A nutshell summary: Most weather stations are located in or near large urban areas, which show artificial localized warming due to what's called the 'urban heat island effect'. Stand outside in the middle of an asphalt parking lot on a sunny day, and you'll begin to get the drift. However, weather stations in rural areas, as well as temperature measurements from weather balloons and satellites, show absolutely _no_ warming trend.

So, basically, our cities are getting warmer, but the planet as a whole is not.



[ Parent ]

Re: The idea of environmental exploitat... (none / 0) (#30)
by rusty on Sun Jun 11, 2000 at 11:53:19 PM EST

There's evidence for both theories, and a few others as well. I'm definitely not equippped to make a good argument either way, so I won't. That was Ryan's argument though-- and the weak link is definitely whether or not humanity has anything to do with the El Nino patterns. The rest of his chain of evidence was pretty solid I thought.

____
Not the real rusty
[ Parent ]
Re: The idea of environmental exploitat... (none / 0) (#33)
by Anonymous Hero on Mon Jun 12, 2000 at 07:28:07 AM EST

On the contrary, there's some pretty strong evidence that 'global warming' is bunk.

That's a fairly sweeping statement. I checked the link that you provided and as far as I could tell, it made no reference to the measured increse in CO2/CH4 in arctic ice cores since the begining of the industrial revolution.

Neither does it apparently make any reference to the observed decrease in antarctic ice fields.

As for Mr Daly's attack on Greenpeace, that's understandable. They have a very vested agenda ( but then so do a lot of people, including, apparently, Mr Daly ).

At this point in time, the debate continues in the scientific community and the emerging concensus ( at least outside of the USA ) is that there is cause for concern. We still aren't certain of a lot of things, but over the last five decades, the scientific community has learn't that it's better to be safe than sorry.

So while it's neither an accepted fact, neither is it 'bunk'. Research into the subject is an ongoing process and it may well be another decade or more before we really know one way or the other.

As for the general question of human impact on the environment, that can be pretty much assumed. What the debate is about is the extent to which we are effecting natural systems so that we can formulate intelligent policies for resource management that are based neither upon the making of a fast buck no matter what or an alarmist over reaction.

In short, it's a balencing act. At this point in time, my own opinion is that the balence is very much tilted towards the almighty buck with very little consideration for future generations. Because of that, while I don't approve of the scare mongering that groups like GreenPeace engage in, neither do I dismiss the publics concerns over the matter.

You might be strangling my chicken, but you don't want to know what I'm doing with you hampster.



[ Parent ]

Darwin turns in his grave (3.50 / 2) (#12)
by oxidised on Sun Jun 11, 2000 at 04:34:38 AM EST

The reviewer is correct to say that intention and other anthropomorphic characteristics should not be ascribed to viruses. But Ryan's apparent invocation of natural selection, rather than chance mutation, to explain the sudden but very rare appearance of highly pathogenic viruses is seems fundamentally flawed, because it would require that the virus somehow "knows" that its usual host is under threat. And even that ascribes some sort of "host preference" to the virus - as if a virus "prefers" monkeys living undisturbed in the jungle to humans. The virus doesn't care. So how are strains of the virus which happen to be more pathogenic in "non-usual" hosts selected over time. Sounds like bullshit to me.

We should all be worrying instead about infant diarrhoea disease caused by lack of clean drinking water, tuberculosis, malaria, hepatitis B (and C) and other commonplace communicable diseases which kill tens of millions every year, but all of which we know how to fix, if only the developed countries could spare the modest resources required....
Sincerely, Oxidised.

Re: Darwin turns in his grave (none / 0) (#14)
by FlinkDelDinky on Sun Jun 11, 2000 at 07:52:05 AM EST

We should all be worrying instead about infant diarrhoea disease caused by lack of clean drinking water, tuberculosis, malaria, hepatitis B (and C) and other commonplace communicable diseases which kill tens of millions every year, but all of which we know how to fix, if only the developed countries could spare the modest resources required....

This is one of those things that bug me too. AIDS research is a prime example. We've spent big dollars that have resulted in effective big dollar treatments that can only be afforded by a few rich westerners.

I know the comparison is a bit artificial but the bang for the buck says we should first build some nice sanitary sewer systems then maybe control disease vectors like moscitos and rats in some of these 'developing' countries. Actually If we did this I think conditions like AIDS would go down simply because people wouldn't be 'worn down' by other diseases. They'd be less vulnarable to infection in general.

[ Parent ]

Re: Darwin turns in his grave (none / 0) (#15)
by rusty on Sun Jun 11, 2000 at 02:55:08 PM EST

Yes. This is another one of Ryan's major points in this book-- most westerners think epidemic disease is something that happens "elsewhere", but today, "elsewhere" is only 10 hours away by airplane, no matter where it is. If we don't assist developing countries with these problems, they'll end up in our backyard next.

As for the "intentionality" of evolution, you'd really have to read the book to get a better grasp on how he's saying that works. It's not implausible, when he argues it-- I just kind of necessarily had to oversimplify.

____
Not the real rusty
[ Parent ]

Re: Darwin turns in his grave (none / 0) (#16)
by FlinkDelDinky on Sun Jun 11, 2000 at 03:18:49 PM EST

As for the "intentionality" of evolution, you'd really have to read the book to get a better grasp on how he's saying that works. It's not implausible, when he argues it-- I just kind of necessarily had to oversimplify.

I didn't have a problem with that idea myself. The way I see it is that these 'invasions' have occured with great enough frequency that nature via natural selection had evovled virii that could 'jump' destructively to another species.

I don't think it's that far fetched (and I haven't read the book). We talk about 98-99% genetic kinship with chimps, but we're probably highly similar to all mammals.

Hell, in the tree of life I learned in school there were two kindoms, plants and animals, with a reallu minor third that group that were unicellular combinations of plant type and animal type characteristics. But now, a geneticist has shown (sorry no link, this is from PBS, maybe Nova) there are five kingdoms. Guess what, genetically speaking, plants and animals are nieghboring twigs on the same branch! Pretty amazing.

I wonder how much of our genetic code is 'this is a human' and how much is 'this is such and such a cell'. You know what I'm saying.

I kind of see it as OO programming, the end result may not look like any other program but 99% of the code comes from objects and libraries previously developed for other uses.

[ Parent ]

Re: Darwin turns in his grave (none / 0) (#18)
by rusty on Sun Jun 11, 2000 at 03:38:10 PM EST

Yeah, viruses can jump species very efficiently, even in species that don't apparently share much genetic similarity. Many human diseases have their natural reservoir in rodents, and for a weird example, you know where the flu comes from? Ducks! Most viruses only have RNA, which defeats the "ECC" features of DNA, so they tend to mutate very rapidly and fairly wildly, too.

____
Not the real rusty
[ Parent ]
Re: Darwin turns in his grave (none / 0) (#21)
by Anonymous Hero on Sun Jun 11, 2000 at 03:56:28 PM EST

Not just ducks. Avian flu (all manner of birds) and swine flu are closely related to primate flu. The flu virus is just not that picky about its hosts. The particular combination of birds, pigs, and people happens to match very closely a common farm life combination in Asia. The high rate of species hopping is more the result of the close living quarters of these species and not a particular species favoritism. Avian flu is found in wild North American birds also, but rarely hops to primates.

[ Parent ]
Re: Darwin turns in his grave (none / 0) (#23)
by rusty on Sun Jun 11, 2000 at 04:09:12 PM EST

Hence new flu strains are usually called "Chinese flu".

____
Not the real rusty
[ Parent ]
Re: Darwin turns in his grave (new strains of flu) (none / 0) (#25)
by oxidised on Sun Jun 11, 2000 at 05:29:21 PM EST

Rusty writes:

Hence new flu strains are usually called "Chinese flu".

Newly discovered strains of flu are named after the city or country in which they are first isolated. This does not mean that they first "developed" there, contrary to popular belief. The flu virus has a very unusual structure which allows it to mutate (or actulaly, re-arrange itself) spontaneously with great ease, in a stochastic fashion. Since China has about 20% of the world's hosts (people), not surprisingly a disproportionate number of strains are isolated there. India also has a lot of people but not many virology labs, hence the relative rarity of flu strains with Indian names.


Sincerely, Oxidised.
[ Parent ]

Re: Darwin turns in his grave (new strains of flu) (none / 0) (#32)
by rusty on Mon Jun 12, 2000 at 12:25:47 AM EST

Right. I should have added "by the media" to "usually called". They get named for real according to location, but often an outbreak of a new flu gets promulgated in the news as "Chinese flu". Of course, we all know how much resemblance news reports generally bear to reality. :-)

____
Not the real rusty
[ Parent ]
Re: Darwin turns in his grave (proximity of develo (none / 0) (#24)
by oxidised on Sun Jun 11, 2000 at 05:21:08 PM EST

Rusty writes:

Yes. This is another one of Ryan's major points in this book-- most westerners think epidemic disease is something that happens "elsewhere", but today, "elsewhere" is only 10 hours away by airplane, no matter where it is. If we don't assist developing countries with these problems, they'll end up in our backyard next.

Well, yes, but is it possible that people in wealthy Western countries ought to help poor people in developing countries control communicable diseases because it is the morally or ethically correct thing to do, rather than purely out of self interest and fear that they might "come over here and infect us"?


Sincerely, Oxidised.
[ Parent ]

Re: Darwin turns in his grave (proximity of develo (none / 0) (#27)
by rusty on Sun Jun 11, 2000 at 06:22:59 PM EST

Whatever floats your boat. :-) I'm a pragmatist, personally, and it's the ethically right thing to do, but most people are much more swayed by "your kids will die" than "my ethics require you to".

____
Not the real rusty
[ Parent ]
More explanation (5.00 / 1) (#17)
by rusty on Sun Jun 11, 2000 at 03:35:09 PM EST

But Ryan's apparent invocation of natural selection, rather than chance mutation, to explain the sudden but very rare appearance of highly pathogenic viruses is seems fundamentally flawed, because it would require that the virus somehow "knows" that its usual host is under threat.

I totally failed to do justice to the argument in the review, kind of out of necessity, as it would have severely bloated my review. For the best description, do read the book. But let me see if I can explain that bit a little better.

As far as we can tell, every species of life on Earth has many endemic viruses that do little or no harm to the host species. They use our biological machinery to reproduce, but the host is unharmed by them. It would look like a classic symbiotic relationship, except that no one has been able to figure out why species tend to select to accomodate the virus, rather than the annihilate it altogether.

So imagine this scenario. There are two species of monkey, Monkey A and Monkey B. Each species gets a new virus. Over time, both species evolve to cope with this new threat-- Monkey A, through natural selection, becomes totally immune to the virus, their defenses alter to wipe out infections as soon as they occur. Monkey B evolves to accomodate the virus-- it can reproduce in their systems without harming the host. Either of these possibilities are equally plausible, and it's probably a matter of chance which happens first.

So now you have two species of monkey, one of which harbors a symbiotic virus, and the other does not. Now imagine that some local human tribes move into the monkey's habitats, to cut down trees and plant crops. Naturally, they will come into close contact with the local fauna, and threaten their habitat. Monkey A, which has no virus, just quietly dies out.

Monkey B, though, has a virus that it has coevolved and nurtured in the population. As luck would have it, this virus mutates easily, and can live equally well in the human genome as in the monkey genome (the two are only about 2% different). Monkey B's virus infects humans, and in the slash-and-burn world of the human immune system, only the particularly aggressive strains of the Monkey B virus survive. These infect the human interloper, and aggressivly try to propagate themselves, killing most of the intruding humans. The humans are no longer able to threaten the monkey's habitat, and monkey species B survives.

The reason this pattern works is because there are a lot of viruses, and many of them are able to species-hop. This theory potentially explains why viruses don't just get wiped out entirely-- species' that evolve to accomodate them now have a sort of "emergency defense" system, which overall helps the species to survive longer. Obviously this doesn't happen with most viruses, but you only need it to work once to be worthwhile.

What Ryan argues is the problem, is that human behavior has thrown a kink in this whole process. We are now hyper-mobile, and one small tribe invading a new habitat can potentially spread an infection to the rest of the species, worlkdwide. This, argues Ryan, is the real danger to us now. Hopefully this makes the mechanics of his theory a little clearer. :-)

____
Not the real rusty
[ Parent ]

Re: More explanation (5.00 / 1) (#28)
by oxidised on Sun Jun 11, 2000 at 06:52:37 PM EST

Rusty writes and Oxidised rejoins:

As far as we can tell, every species of life on Earth has many endemic viruses that do little or no harm to the host species. They use our biological machinery to reproduce, but the host is unharmed by them. It would look like a classic symbiotic relationship, except that no one has been able to figure out why species tend to select to accomodate the virus, rather than the annihilate it altogether.

OK

So imagine this scenario. There are two species of monkey, Monkey A and Monkey B. Each species gets a new virus. Over time, both species evolve to cope with this new threat-- Monkey A, through natural selection, becomes totally immune to the virus, their defenses alter to wipe out infections as soon as they occur. Monkey B evolves to accomodate the virus-- it can reproduce in their systems without harming the host. Either of these possibilities are equally plausible, and it's probably a matter of chance which happens first.

Presumably the "new virus" is a mutation? And immunity to a particular pathogen is not inherited (natural selection does not work like the Lamarckian evolution portrayed in Pokemon...). Perhaps over many generations a species' immune system may evolve to better recognise and deal with certain types of virus, but immunity to a particular strain of virus is not conferred from one generation to the next. Just because your mother had the chicken pox doesn't mean that you won't. Sorry.

So now you have two species of monkey, one of which harbors a symbiotic virus, and the other does not. Now imagine that some local human tribes move into the monkey's habitats, to cut down trees and plant crops. Naturally, they will come into close contact with the local fauna, and threaten their habitat. Monkey A, which has no virus, just quietly dies out.

Monkey B, though, has a virus that it has coevolved and nurtured in the population. As luck would have it, this virus mutates easily, and can live equally well in the human genome as in the monkey genome (the two are only about 2% different). Monkey B's virus infects humans, and in the slash-and-burn world of the human immune system, only the particularly aggressive strains of the Monkey B virus survive.

Whoa! You lost me there. Why does human encroachment which may put pressure on the Monkey B population select for "particularly agressive strains of the Monkey B virus". I would have thought the opposite is the case - those monkeys infected with less aggressive strains of the virus are more likely to survive the onslaught of human habitation.

These infect the human interloper, and aggressivly try to propagate themselves, killing most of the intruding humans. The humans are no longer able to threaten the monkey's habitat, and monkey species B survives.

Fiendlishly clever, those viruses! You are ascribing intention to the virus. Remember, one particuar virus particle does know and doesn't care whether its sibling virus particles are living happily in Monkey B's or not. In any case, surely it would be better for the virus not to kill all the humans, but rather to continue to propogate within humans as well. But they don't do this because viruses are dumb, they can't make such judgements, and they can't direct their own evolution.

The other problem is that a virus which is not highly pathogenic in one species is not likely to be highly pathogenic in another species. There may be subtle differences, but a benign virus in monkeys is highly unlikely to kill humans in a few days.

...snip... What Ryan argues is the problem, is that human behavior has thrown a kink in this whole process. We are now hyper-mobile, and one small tribe invading a new habitat can potentially spread an infection to the rest of the species, worlkdwide. This, argues Ryan, is the real danger to us now.

Yes, but we also now have excellent communications and an organised global response to such emerging problems. Vigilance is necessary but it is unlikely that an exotic virus would cause an overnight catastrophe.

None of this justifies cutting down rainforests etc, its just that you shouldn't use some half-baked argument about exotic viruses to oppose ecologically damaging or non-sustainable "development". There are better arguments against it.


Sincerely, Oxidised.
[ Parent ]

Re: More explanation (none / 0) (#31)
by rusty on Mon Jun 12, 2000 at 12:22:31 AM EST

No, no, no. I'm still not making this thing clear. Let me try one more time.

First:

And immunity to a particular pathogen is not inherited (natural selection does not work like the Lamarckian evolution portrayed in Pokemon...).

That's not entirely true. I know what you're saying, that having antigens to a particular virus in your immune system is not inherited-- that's correct. *But* not being susceptible to infection at all is inheritable. There's an example of rabbits in Australia where this was the case. 99.8% of rabbits in Western Australia were killed by a particular virus. The only ones who survived infection were the ones who never got infected at all, due to, presumably, not having the sequence of proteins that the virus could bind to. This is a genetic trait, and will likely be inherited.

So, imagine that Monkey A, in my example, does this-- it is virus free because it has evolved (rather quickly, one presumes) to not even be infectable by this virus. Monkey B does what you say, that is, it's immune system becomes different, and can suppress infections before they become lethal to the animal, but otherwise will carry the virus.

Where the "first" virus comes from is immaterial. We're just taking a snapshot in the whole cycle, in this imaginary example.

Whoa! You lost me there. Why does human encroachment which may put pressure on the Monkey B population select for "particularly agressive strains of the Monkey B virus". I would have thought the opposite is the case - those monkeys infected with less aggressive strains of the virus are more likely to survive the onslaught of human habitation.

Not aggressive in the host monkeys-- the virus continues to be harmless to it's host monkey. Aggressive in the humans! That is, monkey->human contact gets some quantity of virus into the humans. Once there, inside the humans, who are new here, the virus must run the whole gauntlet of human immunological defenses. In the vast majority of cases, the virus will not infect the new host; it'll either be successfully fought off by the immune system, or else will not find cells it can bind to and use in it's new, unfamiliar host.

But, think about the cases where there are cells in the human that can be used to reproduce by the monkey virus. Which forms of virus are likely to be most successful in this new genome? It makes sense to me that it will be the ones that aggressively propagate themselves, without regard to the well-being of their host. Maybe out of one hundred virus "invaders", 99 of them are programmed to find a cell, make ten copies of themselves, and then escape the cell without causing it further harm (probably killing that cell, but not really going all out), but one has a twist, that doesn't limit it's reproductive cycle to ten copies. It'll go all out, until there's no more raw material in a cell. Then every one of it's offspring will do the same.

While the "ten-copies" strain is getting wiped out by immune response, the "infinite-copies" strain is able to survive, sheerly through encoded aggressiveness, long enough to establish itself in the host. The likelihood is, an infection like this will be severe, if not fatal, to the host human. That is what I mean when I say "selects for aggressiveness".

Of course I don't think that viruses are "directing their own evolution". People anthropomorphize all the time. I don't really think that my computer hates me, when it fails to run some software. I don't think that computer viruses actually "hunt out weak systems". It's simply a convenient way to shorthand a description of very complex mechanical processes. Please make some effort to look past any anthropomorphic language I may inadvertently use, and understand the process behind my description.

The other problem is that a virus which is not highly pathogenic in one species is not likely to be highly pathogenic in another species. There may be subtle differences, but a benign virus in monkeys is highly unlikely to kill humans in a few days.

Of course. However, all species carry lots of viruses. It only takes one that is as dreadfully fatal as Ebola, for example. The "statistics" argument is comforting, but ultimately unhelpful, because I can name you at least three viruses that are harmless to their host species, and nearly always fatal to humans. We know that it does happen. Whatever the odds against it, they're not long enough that it's not a threat.

Yes, but we also now have excellent communications and an organised global response to such emerging problems. Vigilance is necessary but it is unlikely that an exotic virus would cause an overnight catastrophe.

I don't know if the situation has changed significantly since 1997, but one of the arguments Ryan takes great pains to make is that we don't have nearly the global capacity to respond to a serious pandemic that most people think we do. The US, with USAMRIID and the CDC has an excellent infrastructure. In the rest of the world, it's spotty at best. Porton Down in England, the Pasteur Institute in France and Africa, then after that, it's pretty catch-as-catch-can. Maybe it's better now. I don't have any more current information.

None of this justifies cutting down rainforests etc, its just that you shouldn't use some half-baked argument about exotic viruses to oppose ecologically damaging or non-sustainable "development". There are better arguments against it.

This is just one more brick in the growing wall of evidence that we are doing real harm to ourselves as a species in the process of harming the rest of the planet. It's not, in and of itself, an argument that's going to change anyone's mind. And anyway, it's far too complicated to boil down into a coherent sound-bite that you can feed the suburban moms. I don't think it's half-baked though. Ryan is not a kook-- he's a well-respected physician, and this is a meticulously researched and argued book. I'm just trying to do it some justice here-- I know it can sound kind of implausible. But the evidence in support of his theory, is, I think, pretty strong.

I've very much enjoyed this little exchange by the way. Thank you. :-)

____
Not the real rusty
[ Parent ]

Re: More explanation (none / 0) (#29)
by ccweigle on Sun Jun 11, 2000 at 08:14:35 PM EST

As far as we can tell, every species of life on Earth has many endemic viruses that do little or no harm to the host species. They use our biological machinery to reproduce, but the host is unharmed by them. It would look like a classic symbiotic relationship, except that no one has been able to figure out why species tend to select to accomodate the virus, rather than the annihilate it altogether.

The "survival-of-the-fittest"-ic answer would be that developing the ability to accomodate the virus would divert less energy from other important tasks (like eating, sleeping, reproduction, etc) than would fighting the virus (and maintaining a fever, coughing, vomitting, etc).

Of course, I have problems with the rest of it -- the virus that attacks the interloper because it's upsetting the local order. Going back the the ant example mentioned ... somewhere ... we know from study that ants behave both territorially and, er, colonially. There isn't (a. so far, b. as far as I know) evidence of similar behavior in viruses. So I think this theory ascribes a bit too much "behavior" to the virus.

[ Parent ]
Re: More explanation (none / 0) (#34)
by Anonymous Hero on Mon Jun 12, 2000 at 07:54:14 AM EST

...every species of life on Earth has many endemic viruses that do little or no harm to the host species.

Apparently there are an average of at least seven virus's for every other type of organism, including unicellular life forms.

except that no one has been able to figure out why species tend to select to accomodate the virus, rather than the annihilate it altogether.

One theory is that's it's due to viral DNA transfer. When a virus jumps species, it can take a piece of the original hosts DNA with it and this can then be incorporated into the new host ( if it isn't killed outright in the transfer ).

( This kind of transfer has been documented in unicellular organisms, but I'm not sure about multi-cellular life forms. ).

So basically, this means that if your not totally resistant to viral infection, then your species will occasionally get a boost by these transfers that means that more resistant species won't be able to compete with you.

So it goes. Lousy for the individual, but good for the species, since it gets to pick up DNA information that would otherwise take the species a much longer time to aquire by the mutation / natural selection cycle.

There are two species of monkey, Monkey A and Monkey B.

One point that I can add here - different species of monkeys in the Amazon that get into turf wars with each other have been documented to regularly spit at each other and it has been verified that this will transfer virus's between them. So this kind of 'biological warefare' appears to be fairly common between competing species in rainforests.

You might be strangling my chicken, but you don't want to know what I'm doing to your hampster.



[ Parent ]

Re: More explanation (none / 0) (#36)
by porkchop_d_clown on Mon Jun 12, 2000 at 12:43:56 PM EST

The reason this pattern works is because there are a lot of viruses, and many of them are able to species-hop. This theory potentially explains why viruses don't just get wiped out entirely-- species' that evolve to accomodate them now have a sort of "emergency defense" system, which overall helps the species to survive longer. Obviously this doesn't happen with most viruses, but you only need it to work once to be worthwhile.

... While this (co-evolved diseases acting as a defense against competing species) makes sense on the surface, is there any evidence of it actually occurring?



People who think "clown" is an insult have never met any.
[ Parent ]
Viral/host adaptation like incremental development (none / 0) (#35)
by jabber on Mon Jun 12, 2000 at 10:44:22 AM EST

If we squint at the situation, and see it thus:

Species-jumping and symbiosis are two distinct, sequential mutations. It is necessary to jump species first, and only after this has been done, can work towards NOT KILLING the new host begin.

We develop code this way - first we get it to compile, then we get it to load, then we get it to correctly execute without crashing. Nobody writes perfect software the first time, and hardly any source code (not so designed) can easily be ported to a new platform in one iteration.

When a virus spreads to a new species, it has compiled and loaded, but it can't quite execute correctly yet. It takes many 'generations' of mutation to get the non-lethality right, since the virus has to adjust itself (mutationally speaking of course) to the new host's biology. It spreads to multiple individuals in the new species as aggressivley as it can - since as the open source dogma goes: With enough hosts, all mutations are shallow.

Eventually the program executes correctly, and the host organism survives long enough to procreate - and eventually the offspring also survives - and we have a symbiotic virus/host relationship, and the virus comes out of beta testing.

[TINK5C] |"Is K5 my kapusta intellectual teddy bear?"| "Yes"
[ Parent ]

Re: Viral/host adaptation like incremental develop (none / 0) (#37)
by Anonymous Hero on Mon Jun 12, 2000 at 03:32:47 PM EST

Species-jumping and symbiosis are two distinct, sequential mutations. It is necessary to jump species first, and only after this has been done, can work towards NOT KILLING the new host begin.

Except that pathogenicity (i.e. killing or harming the host) requires the virus to use the host's cellular machinery to manufacture particular protiens which disrupt the cell in some way. The ability to manufacture proteins requires a higher level of adaptation of the virus to the host, not a lower level.

This is born out in practice: most viruses which species jump have a lower level, or at worst about the same level of pathogenicity in the new host species as they did in the original host species. I can't think of a single example of a virus which is not very pathogenic in one species suddenly jumping to another species and at the same time becoming highly pathogenic. Does Ryan give any examples of this. Not mutation AFTER species jumping but the same virus having markedly different worse effects in a new host species.



[ Parent ]

What me worry? (none / 0) (#13)
by caliban on Sun Jun 11, 2000 at 06:47:46 AM EST

Viruses?

Whats the big deal, after all, I'm using Linux, right?

*sorry*

Virus X: Tracking the new killer plagues | 36 comments (36 topical, 0 editorial, 0 hidden)
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