Can viruses die of old age? can bacteria for that matter? also, how can a parasite like viruses survive when they kill host (especially quick acting ones like ebola)? wouldn’t they run out of hosts?
Viruses can lie dormant forever and then come to “life” if they come into contact with a host under the right conditions.
They won’t die from old age, since they are constantly dividing. They can die off for different causes other than aging.
A virus that killed all the hosts it came into contact with and which spread easily would certainly run out of hosts. According to the rules of the survival of the fittest this would not be very efficient.
“That is not dead which can eternal lie,
And with strange aeons, even death may die.”
-H.P. Lovecraft
Some (well, a lot of) people will say that viruses aren’t alive, because they have no processes of their own, and must hijack the machinery of living cells to reproduce. They don’t eat or respirate, they don’t move themselves, and they reproduce by physically injecting gentic information into a cell and waiting for the cell to act on that information.
If you use a definition of life that excludes viruses, then by definition, a virus cannot die. That’s a tautology.
A virus can, however, lay dormant outside a host for a certain amount of time. Some viruses are better at this than others: A cold virus (one of the multiple kinds of viruses that can cause the common cold in humans) can lay happily on a doorknob and still be an infection risk for up to five or six hours until some schlub picks it up and introduces it to a mucous membrane, but HIV in the same conditions wouldn’t last nearly as long. (The CDC has been able to keep the virus viable for weeks outside a host, but only by keeping it in tightly-controlled conditions. Minor variations of heat, humidity, and chemistry will nearly always destroy the virus.)
Bacteria are more active. They can be killed in the traditional sense, as they have cellular respiration and they reproduce on their own. Some bacteria can go dormant for a very long period of time, however, hiding in rocks for three to six million years. If there is life on Mars, for example, it’s probably long-dormant cells.