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| Zitterbewegung |
 Posted: Sun Apr 13, 2008 2:08 am Post subject: What makes some viruses more contagious than others? |
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I was pondering the question: What exactly determines how contagious a virus is?
I mean, there are viruses like measle, small pocks or rubella that are extremely contagious and would spread like wildfire without vaccination. But others like e.g. rabies or HIV require real infiltration. What's the reason behind this?
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| free radical |
| Posted: Sun Apr 13, 2008 7:24 am Post subject: |
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Forum Senior
Joined: 24 Sep 2007
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| Google 'virulence factors.' One example is how long the virus can survive outside a host. |
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| i_feel_tiredsleepy |
| Posted: Sun Apr 13, 2008 11:26 am Post subject: |
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| It is also highly dependent on the host receptor recognized by the virus. For example HIV recognizes the CD4 receptor on T cells, so it would have to come into contact with T cells to infect a person. |
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| Jinn |
| Posted: Sun Apr 13, 2008 1:16 pm Post subject: |
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| And also it would depend how much the virus has evolved/adapted. If the virus has evolved to the point where it can survive a long period of time outside the host and can be transmitted through the air then it would be allot more contagious than a virus that can only be transmitted through some bodily fluids (such as HIV) |
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| paralith |
| Posted: Sun Apr 13, 2008 3:54 pm Post subject: |
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In viruses, as well as with most other pathogenic organisms that live in and cause damage to their host, there is a trade-off between the ease with which the virus spreads, and how much damage they inflict on their host.
A virus that kills its host in a few days has to be able to spread to a new host before its original host's death - otherwise, the virus will die with their host. However, a virus that allows its host to live for a very long time does not require a fast method of transmission. These mechanics of natural selection result in viruses with varying adaptations for transmission, including such things as how long they live outside of their host.
Just look at smallpox vs. HIV. A person with smallpox that receives no treatment dies very quickly, and also spreads more quickly. A person with HIV can live for quite some time, and usually doesn't die from the virus itself at all but from their resultingly weak immune system.
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Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
~Jean-Paul Sartre
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| Zitterbewegung |
| Posted: Mon Apr 14, 2008 6:52 am Post subject: |
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Things start to clear up. Thanks to everyone for pointing me in the right direction.
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| i_feel_tiredsleepy |
| Posted: Mon Apr 14, 2008 8:21 am Post subject: |
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| paralith wrote: |
In viruses, as well as with most other pathogenic organisms that live in and cause damage to their host, there is a trade-off between the ease with which the virus spreads, and how much damage they inflict on their host.
A virus that kills its host in a few days has to be able to spread to a new host before its original host's death - otherwise, the virus will die with their host. However, a virus that allows its host to live for a very long time does not require a fast method of transmission. These mechanics of natural selection result in viruses with varying adaptations for transmission, including such things as how long they live outside of their host.
Just look at smallpox vs. HIV. A person with smallpox that receives no treatment dies very quickly, and also spreads more quickly. A person with HIV can live for quite some time, and usually doesn't die from the virus itself at all but from their resultingly weak immune system. |
Also, selective pressure can be applied through the immune system, if a person can fight off the virus in 1-2 weeks then the virus also needs to be able to spread quickly. This is the case with the Rhinoviridae and Adenoviridae that cause the "common cold". Or viruses like Influenza viridae undergo a lot of recombination and mutation to continuously keep ahead of the immunity of the host.
Although, that is really addressing the reason why viruses have different infectivities, and not how. |
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| paralith |
| Posted: Mon Apr 14, 2008 8:27 am Post subject: |
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| i_feel_tiredsleepy wrote: |
| Although, that is really addressing the reason why viruses have different infectivities, and not how. |
I know. But the OP asked, what determines how contagious a virus is, and I think answers at various levels of biology are all appropriate. You guys covered the proximate causes well enough, so I went for the ultimate causes.
_________________
Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
~Jean-Paul Sartre
Monkeys in Clothes - hosted by SFN blogs |
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| i_feel_tiredsleepy |
| Posted: Mon Apr 14, 2008 8:31 am Post subject: |
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Posts: 376
Location: Montreal
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| paralith wrote: |
| i_feel_tiredsleepy wrote: |
| Although, that is really addressing the reason why viruses have different infectivities, and not how. |
I know. But the OP asked, what determines how contagious a virus is, and I think answers at various levels of biology are all appropriate. You guys covered the proximate causes well enough, so I went for the ultimate causes. |
I suppose I as a student of microbiology have been brainwashed to always look at things at the biochemical level and leave the questions of evolution up to the regular biologist  . |
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| paralith |
| Posted: Mon Apr 14, 2008 8:35 am Post subject: |
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| i_feel_tiredsleepy wrote: |
| paralith wrote: |
| i_feel_tiredsleepy wrote: |
| Although, that is really addressing the reason why viruses have different infectivities, and not how. |
I know. But the OP asked, what determines how contagious a virus is, and I think answers at various levels of biology are all appropriate. You guys covered the proximate causes well enough, so I went for the ultimate causes. |
I suppose I as a student of microbiology have been brainwashed to always look at things at the biochemical level and leave the questions of evolution up to the regular biologist . |
Then un-brainwash yourself, my dear! I am no doubt biased since evolution is my favorite subject, but it is intrinsic to all fields of biological study. It's always good to keep in mind all levels of analysis, even if you mostly focus on one or two of them.
_________________
Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
~Jean-Paul Sartre
Monkeys in Clothes - hosted by SFN blogs |
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| why-and-how |
| Posted: Thu May 08, 2008 3:07 am Post subject: why are some viruses more contagious than others? |
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Joined: 26 Apr 2008
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| As far as my knowledge extent, how contagious a virus is depends on its type, and, therefore, its structure and components. The viral envelope,for example, affects greatly the virus (contagiousness). This envelope helps the virus enter the host cell by fusion of the envelope with the host cellular membrane. |
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| NeptuneCircle |
| Posted: Sun May 11, 2008 2:50 pm Post subject: |
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Proximate answers actual require some knowledge, ultimate answers you can just bullshit  |
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| paralith |
| Posted: Sun May 11, 2008 3:50 pm Post subject: |
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Joined: 06 Jun 2007
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| NeptuneCircle wrote: |
| Proximate answers actual require some knowledge, ultimate answers you can just bullshit |
You can bullshit proximate answers too. They just won't be correct.
_________________
Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
~Jean-Paul Sartre
Monkeys in Clothes - hosted by SFN blogs |
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