The red stains on the wall are poryphrin from sneezing, along with some urine. (Just keep that in mind) The stain around the nose is an indicator or stress, or illness, allergies. Most of my rats do not have the staining around their noses or eyes very often.
If your trying to breed, the male will breed her when she is in heat. They will go at quite often when she is in heat. I don't actually know if illness stops them from getting pregnant, but I don't think it would factor in that much.
Some rats just dont deal well with myco, and will never shake the initial symptoms without antibiotic treatment. Always best to choose animals that show little to no sneezing, or staining. Some rats are more resilient to the effects of myco, so practicing selectivity with hold backs is another ingredient to a successful colony.
I can name 4 rats that don't deal well with myco in my colony, two that get very sick from it and are never bred, and 2 get the sniffles often enough for me to be concerned to not hold back from them.