If no one on the entire planet, including animals (if they even get it), had the cold, would it die out?
Is the cold something that has to be passed around in order to stay alive, or can it be contracted from harsh weather conditions?
The cold is caused by a virus. It mutates pretty rapidly, which is why there’s no vaccine for it and why you can catch cold several times a year. As the virus passes through other humans it eventually mutates to the point where your immune system can’t recognize it. [Once again, achoo!] If the word I’ve heard is correct (I’m not checking this statistic) the cold virus can sustain itself indefinitely in human populations of 5000 or more.
Also, a virus can sustain itself for quite some time outside of a host. As it is just a bit of genetic information wrapped in protein, it does not have life functions except when its genetic material uses a living cell to self-replicate. Once that is done, the virus is no longer alive. Neither is the cell. Thousands of new viruses are, however, each of them just waiting to latch on to a cell and repeat the cycle. So goes the viral life cycle, ensuring that we will suffer the common cold for a long time to come.
The common cold is not A virus, its a big bunch, about 200 rhinoviruses…collectively.
Thus, youll have to reformat your question msc75.
Colds can be caused by over 500 different viruses. Some of them are rhinoviruses, but not all. The reason why we cannot build immunity to any of them is because they do not stimulate our permanent memory cells (immunoglobuns). Only one set of Ig is stimulated, and that only provides temporary (about a month) immunity.
Smallpox was caused by a virus which was carried only by homo sapiens. After curing all of us so afflicted, we were able to wipe out that illness. The only living viruses that can cause smallpox are in a laboratory, and there is debate whether they should be killed. (That would be a good topic for GB here. I believe the sooner the better. The argument against is: if we are attacked by a country which releases the virus against us we would have no protection. One lab assistant died from the virus.)
However, everybody was vaccinated for smallpox, which meant we were instilled with the antigens that caused permanent memory cells for the virus to be activated. Since colds are caused by over 500 different viruses, since other animals get colds too, and since they do not activate the permanent memory cells, they would not die out.