Originally Posted by crotalusadamanteus

No offense, but.."temps are fine" is hardly an answer that gives enough info for people to try and help you out. I've heard that answer many times, and when finally get an actual number from them, it turns out that temps were not "fine". Lets try it again.

What are the temps at?
About what level is the humidity at as far as % goes?
What do you use to measure them?
How do you heat the enclosure?
How long have you had the Boa?
Is this the only Boa you have?
What did the vet give you to inject?
What sort of instructions did they give you for injections?

(I ask the latter 2 questions, because I have been given bad instruction from vets that were not really as qualified with reptiles as they led me to believe, and their instructions led to damage from improper injection of certain meds)

Sorry for being direct, but when you ask for help, either from online sources, or a vet, accurate info is the key to getting the answers you might need, and your answer is very vague.

In my experience, if you are seeing bloody saliva, that is more indicative of pneumonia. That is about as advanced an URI as you can get. Not all snakes have one working lung, some have both functional lungs. But this is true of Boas, and only having one functional lung makes URI a very serious with Boas, and possibly a life threatening situation. I have lost a few in my time that I was told "no problem, give them this, and they'll be fine". Never assume with them, and always treat as if they are seriously ill, because in reality, they really are with advanced URI.

Good luck

Rick