Why isn't a simple cold rapidly fatal?

As I understand it, a viral infection like the common cold happens when a virus starts attacking the cells in one’s body. Since an infected cell may produce 100’s of viri, it would seem that unless the body managed to kill all the invaders in the first few cycles, the immune system would be hopelessly outnumbered. But, this clearly doesn’t happen - most colds ramp up quickly and stay at a relatively constant state for a few days, and then resolve. So, why don’t all virus infections lead to rapid death?

The symptoms of a cold occur from the immune system response, not from the damage done by the virus. Once the immune system recognizes an infection from one of the cold viruses, the virus can’t really do much more damage. The way the immune system “fights” the virus is basically by editing the virus’ genetic code, attaching bits of material to it which alters it enough to hopefully make it harmless. Eventually big mean killer cells from the immune system gobble up the altered viruses and eject them.

ETA: the immune system doesn’t really care about numbers, and it can’t really be “outnumbered”. If you have chicken pox antibodies in your immune system, introducing a whole pile of chickenpox viruses through an injection or something won’t really burden your immune system. The antibodies are able to neutralize the viruses and you probably wouldn’t even get the symptoms of an illness.

And any potential ancestors of ours that did succumb to the cold virus early on did not produce viable offspring . . .

I suppose a slighter better formulation of the question would be why are some viruses (Ebola) very dangerous (50-90% fatal) and some (common cold) almost never fatal.

I dont know the answer, but some viruses may be better at hiding from the immune system (AIDS), some only target particular cells (e.g herpes) and dont spread to others, and some may even be designed not to kill the host (e.g. have a self limiting infection rate) so not to kill off the survival source.

“Successful” viruses don’t kill their jost. “Cold” viruses are highly sucessful.

The most successful viruses cause no symptoms at all. One example is cytomegalovirus; most people infected with this virus have no idea that they have it.

It will also depend what tissues the virus evolved to infect. The common cold infects the mucous membranes of your respiratory tract, so it’s not generally going to give you more than the sniffles. Even if your immune system is slow on the defense, a typical cold virus won’t generally go further than causing respiratory symptoms. It helps that rhinoviruses do better at slightly lower temperatures, keeping them happier up in your nose than in your lungs. Hepatitis viruses, however, will aim at your liver and can make you very sick as a result. Ebola attacks the endothelial lining of your blood vessels, making them leaky and prone to bleeding, which can kill you pretty quick.

Different viruses, different target tissues, different symptoms, different levels of seriousness.

er yes that was sort of my point. Some successful viruses do though, at least in the distant past before vaccines and isolation.

Ebola isn’t anywhere near remotely as successful as rhinovirus. Give it another few hundred thousand years, and it’ll either be gone, or a mere inconvenience like the cold.

But Ebola and Marburg are most deadly when transmitted blood to blood. In the book the Virus Hunters, the outbreaks of Ebola in Zaire and South Sudan, were basically caused by reusing needles. This had a horrible effect on the mortality rate.

Ebola transmitted by burial rituals had about a 50% mortality rate. Much lower than the direct needle. Ebola transmitted by close contact (basically bad barrier nursing) was around 15% mortality. With proper barrier nursing, Ebola wasn’t transmitted.

Lassa Fever was also studied and they found if a person knew exactly when they were infected with Lassa Fever, (say through a needle stick) they could look at the body’s own response to it and determain in 12 hours how severe the response to the Lassa Fever was.

The quicker the body was able to respond the less deadly it was.

In a cold you have many things fighting the virus. Macrophages can do a lot of damage to viruses, while T-cells and helper cells can provide additional lines of defense.

Nitpick: As I understand it, HIV “hides” from the immune system by essentially gouging out its eyes and hacking off its limbs, whereon it proceeds to gorge itself on its brain.

The first part makes it sound as though the immune system alters the sequence of the viral DNA or RNA, which of course it doesn’t.

Didn’t the OP answer their own question?

Because the simple cold is a simple virus.

A simple virus still may kill the cell it infects, and still undergoes tremendous amplification each time it successfully infects a cell. So, no, I don’t consider the question answered so far.

I think it’s been answered fairly clearly - you were ignoring the effects of the body’s immune system. What remains unanswered in your mind?

Well, I’m trying to think about the from a simulation standpoint. Something along these lines. If each succeeding generation of virus is 200x greater than the one before, I don’t see how the immune system ever catches up. Or, for that matter, if the immune system is that good, why there is ever any infection at all.

I understand that this isn’t what happens in the real world, i’m just curious as to why the virus load is so carefully balanced - it would seem at first glance to be able to completely overrun any defenses.

I don’t really know jack about epidemiology, but if you’re giving us a link to predator and prey, I think your understanding of infectious diseases is probably plagued from the get go.

Virii aren’t predators so much, and if they were it wouldn’t be sustainable in the long run for the predator to too efficiently kill its prey.

Well nobody has explained how the immune system successfully fights off cold viruses. Post #2 was an attempt, but the explanation about “DNA editing” is incorrect.

I’ll take a knock at a (very simplified) explanation:

Your body has many lines of defense against viral infection. Some are passive. In the respiratory tract, where the cold virus infects, foreign particles are trapped in mucous and swept out of the body. Mucous also contains antiviral proteins.

Note that a virus can’t actively seek out and infect tissues; it just floats around until it happens to bump into the right sort of host cell.

Then there is the innate immune system. Cells like the macrophage basically wander around gobbling up anything that looks vaguely like a virus. Damaged cells trigger the inflammatory response which draws more immune cells to the infected site. Other immune cells kill any sort of infected cell.

Finally there is the adaptive immune system. Whenever something foreign like a virus enters the body, your immune system produces antibodies that bind to that specific virus. These antibodies can cover the virus and make it harmless. They also flag the virus for destruction by immune cells. This process takes a few days to ramp up, but once it does it’s very effective at stopping the infection. After the infection is cleared, your immune system retains a memory of that particular virus, which means it will respond much more quickly the next time.

Very informative. But, it doesn’t answer my question.
Perhaps someone with some real knowledge about virology will be able to answer.
Oh, and in my link, the Rabbits are the Viri.

post #7 answered your question then. the virus only works on certain types of cells that aren’t really vital.