Ivomec / Pet Death

Question
Our beloved Pet Rat Leo died this morning. He had just gone through his second shot of ivomec on Tues 4/20 for treatment of mites. He was released with a clean bill of health heart and chest clear with no signs of infection.Thursday night I got home late and noticed he wasn't eating much and was getting a respiratory infection. This morning I got up rushing to get him to the vet. He had labored breathing and pink mucus around his eyes....before I could get my shoes on to walk out the door we lost our baby boy Leo. He had a clean bill of health on Tuesday and 3 days later he died from a respiratory infection! Could the shots have weakened his immune system? Is it common for a respiratory infection to become fatal in 12 hours or less? How could he be healthy Tuesday and Die Friday? He was in a dust free, chemical free environment. In a large well ventilated cage. What can I do to make sure this doesn't happen to my other boys.
-Leo was kept separately as soon as the mite problem was noticed.

Answer
I am so sorry for your loss.  We always want closure, especially when we lose our rats so suddenly.  

With Leo, I do not think that the Ivomec had anything to do with his death at all. The drug is an anti-parasite and has no bearing on the immune system at all.  What your rat had sounds more like the dreaded Strep pneumonia.  This comes on out of the blue with the first signs of lethargy and anorexia, and can kill anywhere between 12 and 24 hrs later.  Aggressive antibiotic treatment "may" save the rat, but we are talking antibiotics via nebulization, IV and the rat would need to be kept in oxygen the entire time as well. SubQ fluids for dehydration would also be necessary.  It would be a serious deal and would require a very qualified Vet hospital, one that is open 24/7 and could provide round the clock care for critically ill animals.  Strep pneumonia is a secondary infection.  Many people make the mistake thinking that strep throat has caused this type of infection, but it has nothing to do with strep throat.  
It is Streptococcus pneumoniae (pneumococcus)that is responsible.  Just telling you this so that others reading this that may have heard that if you have strep throat it can cause pneumonia in rats, and it is totally UNTRUE.  
Anyhow, this is usually what causes death in rats with respiratory infection and your little guy probably had it. Again, I am really sorry again for your loss!