Baidarka

Here's a question that should be of interest to everyone. When we catch a cold and we hack and cough and sneeze.

Are we using our bodies defences to rid ourselves of a viral enemy?
or
Are we being used and manipulated by the virus in order to project viral spores outside of us to infect others?

This is a simple question of importance to all of us. I think that the differing paradigms of evolutionists and creationists would lead to different conclusions.

Oolon Colluphid

It's mostly manipulation. It's perfectly possible to have a virus that does not cause respiratory secretion to increase. But it's a distinct advantage for a respiratory-mucus-living virus to get itself sprayed around in an aerosol of its host's making.

Successful parasites (which include bacteria and viruses -- they only get called something separate due to historical accident of nomenclature) are the ones that get passed on most. So those that cause the host to change its behaviour, such that it's more likely the parasite will be passed on, are the ones that leave more descendants. This can mean co-opting the host's immune responses such as coughing, or it can be by causing the host to be, eg, more likely to get eaten by the secondary host.

See for instance Zimmer's marvellous <a href="http://www.amazon.com/exec/obidos/ASIN/074320011X/qid=1023278929/sr=8-1/ref=sr_8_1/103-3606307-8864650#product-details" target="_blank">Parasite Rex</a>.

TTFN, Oolon

[ June 05, 2002: Message edited by: Oolon Colluphid ]</p>

RufusAtticus

Please explain.

scigirl

Very good question. The answer is, well it's hard to say.

I do want to point out that our bodies fighting off pathogens, and pathogens fighting to live, provides excellent fodder for evolution. An analogy would be the star wars arms races we see today: threat of death is a wonderful push for complex equipment, right? They make a missle, we make a missle defense system, they make a better missile and so on.

But let's examine the question: What does sneezing or mucous production do? Well, it both spreads the virus, and it helps us get rid of the virus. So, what is happening is a struggle between both virus and host. Did we evolve the sneezing, and the virus just took the opportunity? Or did it evolve to make us sneeze? Who knows.

One aspect to keep in mind is that getting rid of colds is not the only function of mucous or sneezing. These mammalian defense systems evolved under a whole host of pressures (no pun intended), including but not limited to, several different types of bacteria and viruses, the need to keep particulates out of our sinuses, the need to keep membranes moist, etc. So, be wary when using one particular problem for mammals (i.e. rhinovirus) as an explanation for an entire immune organ, or physiological function.

My virology text does has a great description of the immunological arms race, I'll have to post it later.

scigirl

Oolon Colluphid

Which?

That many bacteria and pretty well all viruses ought to be considered parasites? If a parasite is defined as something that spends part of its lifecycle living on or in another organism at the other’s expense (<a href="http://www.amazon.co.uk/exec/obidos/ASIN/0521576911/ref=sr_aps_books_1_1/202-2169284-1592601" target="_blank">Matthews 1998</a>), then to limit it to animals is kingdomist . Based on how they live, it’s not even fair to restrict the definition to eukaryotes. As Zimmer poins out, the easy majority of living things are parasites. Everything has at least one species of parasite. And need I mention bacteriophages?

Or do you mean the historical accident bit? It stems from the harmful ones being discovered as pathogens. They were too small to be seen actually doing stuff except multiplying, so weren’t considered to have a lifecycle as such, at least in the ‘normal’ parasite sense. Also, parasites were for a long time considered degenerate, having ‘devolved’, perhaps, from something better, more noble. So bacteria and viruses got pigeonholed as something separate from the degenerate freeloaders which are normally called parasites.

See Zimmer’s book (which I don’t have to hand -- shame, it has some good quotes on ‘degenerate’ parasites -- but highly recommended) for one of the best discussions of parasites for the lay person.

(Next up on my reading pile is Bush’s<a href="http://www.amazon.co.uk/exec/obidos/ASIN/0521664470/ref=sr_aps_books_1_1/202-2169284-1592601" target="_blank">Parasitism</a>, which is serious stuff but great, and very readable.)

Cheers, Oolon

liquid

Just a quick thought about the original question. Putting aside the cases for viral manipulation, I don't even see a case for body defenses. What possible facility does the sneeze provide for defense against a virus? After all, the battle is immunological and I doubt particularly influenced by the physical reaction of forcibly expelling mucous. After all, the sneeze is a reaction that removes objects from the respiratory passages, and the viruses (virii?! ) are largely within the organism's cells.

scigirl

Actually. . .

Our innate defenses are very important, more than we often realize. Innate defenses include our skin, mucous membranes, sneezing, etc. Consider this: mutations which affect them (such as cystic fibrosis), or injuries which affect them (such as severe skin burns) result in devastating bacterial and fungal infections. Despite the fact that CF patients have a completely functional immune system, the defect in their lung secretion system makes it impossible to remove parasites such as pseudomonas, and in fact it's often what they die from. Same with burn patients--the skin is our first line of defense, and when it's gone, it doesn't matter that we have a bunch of white blood cells around. They simply aren't good enough to protect us from bacteria, without the skin as a first barrier.

True, many microbes have evolved ways to get around one or more of our innate and/or adaptive defenses. But keep in mind, we evolved under a complex interplay between us, and all the microbes at once, as well as other pressures (the need to not get dirt in our sinuses, etc). Sure if someone couldn't make mucous or sneeze, they couldn't spread rhinovirus. But then they would succumb to all the other viruses/bacteria, and probably some other physiological function would be affected as well (all of our innate defenses serve more than one purpose).

scigirl

scigirl

Good point - we actually sneeze from a viral infection because cells infected with the virus have released certain compounds called "cytokines" which activate an allergic response. It's certainly not the best way to get rid of a virus, but it's the only way that this particular system has figured out to get rid of foreign objects.

scigirl

tronvillain

On a similar note, it's been suggested that certain STD's cause a certain itching sensation to promote sexual activity.

scigirl

Yeah nothing makes you wanna do it like a big ole sore on your genitals!

Seriously? I suppose it's possible. . .

scigirl