oh goodness there are different sorts of respitory problems most of them can be spread to other rats and most of them can be treated by antibiotics. If you are having any problems with your rats breathing you should get them to a vet asap
Upper respiratory infections can come from any number of things, it's hard to tell what. Rats with URIs need to be put on antibiotics for a full three weeks. If left untreated, it quickly turns into pneumonia and the rat can die from it. Like Stephanie said, if you hear any congestion or excess sneezing from your rats, take them to the vet ASAP.
You should educate yourself on airborne viruses such as SDA and Sendai - both are killers if not caught early enough and aggressively treated with antibiotics and other medications.
i printed those pages out night and you are right it sounds like what my boys had *tear* and i will be showing them to all of my friend s that take um care of their rats (i so tell them what to do all the time LoL)
I think mamal biology is similar so i guess respiratory problems are like allergy, cold, flu, chest nfection and pneumonia. Humans seem to get mostly viral colds and flu and arent usually treated but from what ive read rats are more vulnerable and are treated-intivirals, antifungals, antbiotics ect. So I spose its like your baby being ill or your Gran.