neverending sneezing - please advise

Hi!

I was given some baby broken marked mice a while back. I felt had been weaned a bit early so I gave them a variety of nice food including soft things so they wouldn't be too stressed by their early move and they seemed to be doing fine, but after about a week they started sneezing.

I immediately read up on mouse sneezing and was preparing myself for the worst as it said mouse RIs can become nasty and fatal very quickly, but they never deteriorated, they seem happy and active otherwise, but are still sneezing more than a month on. I have kept them separate from my original mice (none of which have ever sneezed in over two years that I've kept mice), so chances are they were already carrying the bug when I got them (unless my mice were carrying it without showing symptoms, and I transferred it into the babies' cage on my person).

I have since put one of my mice with them as an experiment and it does not seem to be sneezing a couple of weeks on. Could it be that broken marked ones are particularly prone to whatever sneezy disease this is? Should I do something or can I ignore the sneezing, as it is not getting worse and they seem happy in themselves? (it is definitely not the bedding, I don't use pine shavings).

My own mice have not been breeding well the past six months or so, but are otherwise all in good health and not very old. I was reading about Mycoplasma causing reproductive problems in rodents, could it be that my lot suffer from the reproductive infection and it got transferred to the new babies which are now showing symptoms of the respiratory form?

I am grateful for any and all experiences! Until the beginning of this year I had been very lucky and not had any health problems in my colony except the odd mammary tumour and suddenly now I am having potentially two mysterious illnesses at once.