I have always known that every time you catch a cold...it is a different virus...
When you get better...your body has become immune to that one...and you eventually catch another...
Sad..There will never be a cure for so many I fear...

Most people do tend to think there is a common pathogen called the Cold Virus, when they are actually describing two seperate characteristics of an infection. A "Cold" is simply a list of symptoms associated with several species of viruses, and it has been known for some time that cold-like symptoms can occur with several different genus'. In particular, the same symptoms can occur in individuals infected with Rhinoviruses, Adenoviruses, Parainfluenza viruses, Enteroviruses, Metapneumovirus, and others. Take for instance the family of Picornaviridae under the genus Enterovirus, which are normally associated with infections of Polio, but can also cause other infections in the gastrointestinal tract like an Echovirus. This particular genus of virus also have another species called Coxsackivirus which can cause symptoms associated with the common cold, Meningitis, or Conjunctivitis. The taxonomy of these viruses are very important in understanding how symptoms can vary greatly from species to species, and why there is such diversity associated with their replication.

The Picornaviridae family of viruses are responsible for the greatest amount of symptoms commonly associated with a cold. All viruses found in this family are + sense stranded RNA viruses (that is only one molecule), which means they are much more virulent than their DNA based counterparts, which do not replicate at the same rate. This family is probably one of the largest groups to infect the human species, and has a range of species and sub-species to large to list, but suffice to say most of them share common characteristics which make them extremely difficult to detect. Case in point, there are two species classified under the genus Rhinovirus: Human Rhinovirus A and Human Rhinovirus B, which contain a number of serotypes and sub-species. In fact, Human Rhinovirus A contains around 74 serotypes and Human Rhinovirus B contains another 25. Due to the replication process these viruses are able to replicate at astounding rates and have a number of seperate surface proteins that help them bind to cells.

Once one of these viruses bind to cellular receptors on the cells surface their protein is removed and +ssRNA is translated inside the Cytoplasm, which cleaves the polyprotein to produce more viral proteins by transforming the new -ssRNA into more +ssRNA. The viruses genome dictates that this process be repeated inside the cell and more viral RNA be created for replication until the cell dies. Now, as with many other viruses there is no latency period, so symptoms generally occur quite rapidly and dissolve after a few weeks of infection because instabilities are produced along the way. After a few replication cycles empty viral capsids become quite normal, that is they are defective and contain no RNA and the virus destroys itself with an ineffective means of replication. This process accounts for why there is such a variety of viruses found in this family as they are not the most stable of viruses, and would require a greater diversity of them to establish a long running battle in humans.

Great topic, and I'm glad you brought it to the boards attention! I just wish the article had gone into greater detail about the structure and topology of these new viruses.