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Thank you, I really appreciated this read. Viruses that kill quickly and efficiently do not spread as well as those that cause some disease but allow their hos

by stephth 15y ago

Thank you, I really appreciated this read. Viruses that kill quickly and efficiently do not spread as well as those that cause some disease but allow their host to continue functioning more or less normally (all the while exposing many more to the virus). While this perspective is sound and less alarming than the source, viruses like influenza can still spread relatively far, can't they? They are believed to be contagious one or two days before the onset of symptoms [1], leaving a quite big window open for contagion. [1] When is a person with influenza contagious? A person is most likely to pass on the virus during the period beginning one to two days before the onset of symptoms and ending four to five days after the onset. http://www.vaccineinformation.org/flu/qandadis.asp http://www.vaccineinformation.org/flu/qandadis.asp

jballanc 15y ago
The flu is an interesting beast. Let's say you are a flu virus that has just landed in someone's lung tissue. What's your next move? You had best get inside of a cell, and quick! You see, the human body has agents called white blood cells out looking for you. Ok, now what's your next move? Well, you want to reproduce. Really, that's all you want to do. You don't care if you reproduce in this host or another host, so long as you get the chance to make many, many offspring. The problem is, eventually this host's immune system will catch on and eradicate you. So, you had best make plans to find a new host. Now you have two choices: 1. You could reproduce rapidly. This will allow you to generate the greatest number of viral particles before the host immune system catches on. Unfortunately, as you reproduce your host will become ill. They will be less mobile and more likely to be quarantined, so you might end up coming in contact with fewer potential new hosts. 2. You could reproduce at a measured pace. You'll end up with fewer offspring total before the immune system knocks you out, but if you can leave your host mostly healthy, then they are more likely to bring you in contact with more potential new hosts. As for why you are contagious before the onset of symptoms, that is due to another rather interesting feature of the flu. You see, the flu can cause damage in a variety of different ways. Obviously, taking over the machinery of a cell to make new virus particles is not good for the cell or a tissue. However, that's not the most damaging effect that flu can have. For particularly fatal cases of the flu, what happens is that so many viral particles are produced so rapidly that the body's immune system goes into overdrive. Never underestimate the power of the human immune system, especially the power to kill humans! This is why the Spanish flu, the Swine flu, and H5N1 are most devastating to relatively young, relatively healthy individuals (their immune systems are the strongest). So, the flu symptoms that result from the body's own immune system causing damage will only occur (obviously) once the immune system has already engaged and begun neutralizing the virus. Hence, this is why flu is typically only communicative before the onset of symptoms. Edit: I should add that despite this interesting feature of the flu, almost all diseases are primarily communicable before the onset of symptoms. This has as much to do with the immune system as it does with the fact that generalized symptoms won't set in until the buggers have already been reproducing for a while.
- rdtsc 15y ago
  A silly question: could one craft a virus that would change its reproduction rate profile after so many generations. Say a virus that spreads quickly but is asymptomatic however in X # of generations there is a high probability that it would become very deadly. In way it would have a pre-programmed mutation scheduled in it.
  - Foy 15y ago
    We could call it the Skynet virus.
  - jballanc 15y ago
    Most likely no. This is where the systems biology aspect comes in to play. Stated simply, biological organisms are highly non-linear, tightly intertwined systems. For example, you can develop resistance to malaria, but you'll also end up with sickle cell disease...
  - rdtsc 15y ago
    Hmm why the downvotes? It was stupid question, pardon my ignorance, but just a reply with an explanation would suffice.
  - eps 15y ago
    I would guess that it's doable. There is after all a mechanism that switches off cell replication (division) after certain generations. (edit) Specifically, from NYT article on aging from few days ago - Senescence can also be caused when cells run out of telomeres, the caps at the end of the chromosomes that get shorter at each cell division.
  - rbanffy 15y ago
    You ewould probably end up with a very complex virus. A virus like that would be very likely to mutate into something that doesn't do what you want it to do.
- tokenadult 15y ago
  Ok, now what's your next move? Well, you want to reproduce. Even as an explanatory analogy, it's best to leave teleological explanations out of descriptions of evolutionary medicine. Your point in your grandparent post (the top comment in this thread) is correct that only actual real-world results can show whether an influenza virus is optimally designed (by human beings) to be both highly contagious and highly virulent. But precisely because that is an empirical question, there is no point to hand-waving arguments that a virus "wants" to reproduce. Viruses don't have volition about anything. Some viruses spread through an entire host population and make the host go extinct. It wouldn't help the future of Homo sapiens if a human-killing virus spread rapidly through humankind.

by stephth 15y ago

jballanc 15y ago

The flu is an interesting beast. Let's say you are a flu virus that has just landed in someone's lung tissue. What's your next move? You had best get inside of a cell, and quick! You see, the human body has agents called white blood cells out looking for you. Ok, now what's your next move? Well, you want to reproduce. Really, that's all you want to do. You don't care if you reproduce in this host or another host, so long as you get the chance to make many, many offspring. The problem is, eventually this host's immune system will catch on and eradicate you. So, you had best make plans to find a new host. Now you have two choices: 1. You could reproduce rapidly. This will allow you to generate the greatest number of viral particles before the host immune system catches on. Unfortunately, as you reproduce your host will become ill. They will be less mobile and more likely to be quarantined, so you might end up coming in contact with fewer potential new hosts. 2. You could reproduce at a measured pace. You'll end up with fewer offspring total before the immune system knocks you out, but if you can leave your host mostly healthy, then they are more likely to bring you in contact with more potential new hosts. As for why you are contagious before the onset of symptoms, that is due to another rather interesting feature of the flu. You see, the flu can cause damage in a variety of different ways. Obviously, taking over the machinery of a cell to make new virus particles is not good for the cell or a tissue. However, that's not the most damaging effect that flu can have. For particularly fatal cases of the flu, what happens is that so many viral particles are produced so rapidly that the body's immune system goes into overdrive. Never underestimate the power of the human immune system, especially the power to kill humans! This is why the Spanish flu, the Swine flu, and H5N1 are most devastating to relatively young, relatively healthy individuals (their immune systems are the strongest). So, the flu symptoms that result from the body's own immune system causing damage will only occur (obviously) once the immune system has already engaged and begun neutralizing the virus. Hence, this is why flu is typically only communicative before the onset of symptoms. Edit: I should add that despite this interesting feature of the flu, almost all diseases are primarily communicable before the onset of symptoms. This has as much to do with the immune system as it does with the fact that generalized symptoms won't set in until the buggers have already been reproducing for a while.

rdtsc 15y ago
A silly question: could one craft a virus that would change its reproduction rate profile after so many generations. Say a virus that spreads quickly but is asymptomatic however in X # of generations there is a high probability that it would become very deadly. In way it would have a pre-programmed mutation scheduled in it.
- Foy 15y ago
  We could call it the Skynet virus.
- jballanc 15y ago
  Most likely no. This is where the systems biology aspect comes in to play. Stated simply, biological organisms are highly non-linear, tightly intertwined systems. For example, you can develop resistance to malaria, but you'll also end up with sickle cell disease...
- rdtsc 15y ago
  Hmm why the downvotes? It was stupid question, pardon my ignorance, but just a reply with an explanation would suffice.
- eps 15y ago
  I would guess that it's doable. There is after all a mechanism that switches off cell replication (division) after certain generations. (edit) Specifically, from NYT article on aging from few days ago - Senescence can also be caused when cells run out of telomeres, the caps at the end of the chromosomes that get shorter at each cell division.
- rbanffy 15y ago
  You ewould probably end up with a very complex virus. A virus like that would be very likely to mutate into something that doesn't do what you want it to do.
tokenadult 15y ago
Ok, now what's your next move? Well, you want to reproduce. Even as an explanatory analogy, it's best to leave teleological explanations out of descriptions of evolutionary medicine. Your point in your grandparent post (the top comment in this thread) is correct that only actual real-world results can show whether an influenza virus is optimally designed (by human beings) to be both highly contagious and highly virulent. But precisely because that is an empirical question, there is no point to hand-waving arguments that a virus "wants" to reproduce. Viruses don't have volition about anything. Some viruses spread through an entire host population and make the host go extinct. It wouldn't help the future of Homo sapiens if a human-killing virus spread rapidly through humankind.