What is the lifespan of a single virus cell?
I realize there may be wide variation, but i am just looking for a ballpark figure. Does a single cell live for seconds, minutes, hours, days, weeks.?
As it is not really "alive," the word "cell" does not really apply for a virus. A virus by itself is inert matter with a sheath, and it only becomes active when it invades and takes over a "host" cell. It needs the nucleus of a living cell to be operative.
The "lifespan" or active cycle of a virus depends on which type it is. Some are very vulnerable and can't "live" when exposed to air (AIDS, for example). But once in their element, they flourish and multiply by ravaging living cells around them by appropriating their nuclei matter as their own.
In a way, viruses multiply like spores, and the explosion of new ones is much like a "hatching out" process in which the host cell dies (Think of "Alien.") That is why when you have a flu virus, for example, you know exactly when you are going to "be sick" again by calculating the lapse of time between trips to the bathroom. Fortunately, in the case of influenza, the virus usually weakens over time and "dies" off. We even speak of a 24-, 36- or 48-hour virus, for example.
Unfortunately, many other viruses gain ground in their host environment and don't recede without a fight. Others remain latent even outside of a host and then "come alive" once exposed to a receptive host. (Scientists found such latent viruses in frozen mammoths's saliva and were able to activate them.)
Another reason (besides being "unlive") a virus is so difficult to get rid of is its ability to mutate. Viruses are able to pick up on the profile of immunity cells attacking them, and since they are recognized by the structure of their surface, they simply change their "topography" and go incognito until recognized as the villain again. Or two different viruses might get "the urge to merge" and construct a hybrid of the two, "Lego" style, thus broadening the spectrum of potential hosts. (The H1N1 virus, for instance.)
As cycles of viruses are as variable as the types of viruses themselves, you need to select which ones concern or interest you the most and then do research on that. But the main thing to remember is that they are so elusive and resistant because of their ability to remain latent (don't need a life support system all the time), to profusely reproduce, and to mutate.
The following references should be helpful in understanding how viruses function in terms of theîr host and how they replicate.