what medicine?

[Skiploder]

here's the details:
1, the snake had been infected half a year

2, infrared bulb given to raise the temp

3, secretions are thick, sometimes clear and sometimes opaque

4, the check up results came out with no reaction with any bacteria and disease(i've did 3times) the first result came out with reaction, medicine given, uncured, second reslut, reacted with different kind of bacteria, the most extreme medicine given, uncured, third time, no reaction! vet said"if the medicine given are not helping, i don't have any clue what disease/bacteria it is!" he does mean the medicine at the third time check up

5, secretion continues to obtain, suggested to use betadine with warm water to clean out the mouth, no improevment

6, had tried many kinds of antibiotics that can heal upper respiratory disease, still no improvements and no reaction

NOTE: above information are listed not according to the date and steps, and this is not the first time the snakes got infected, we have 6 carpet pythons died of the same situation, it happens in winter eventhought we provide heat pad

From what you are posting, your vet sounds like a real ass. Your account indicates he feels it was a bacterial infection, and cultured and attempted to treat it as such. When that didn't work, he threw a couple of courses of antibiotic treatment at it. Now he's recommending treating it with betadine rinses?

In all of these visits, he has not offered some theories on what he thinks it might be? A virus? A bacteria? Anything? Really?

If that's the case, go see another vet. Get the file from the original vet which should included all of the tests that were run and all of the medications that were prescribed. That way, you and your snake will not have to endure the same failed course of treatment again. It's important that you and the vet both take some time - you to clearly and concisely described what is currently happening, what treatments were tried, that other animals in your care have been infected and died, etc. - and him to listen to what you have to say.

If it's a bacterial infection, it can be cultured and an antibiotic prescribed. If it's a virus, well, then that's a different story. Flushing the mouth out with betadine is useful for something like stomatitis, not a systemic bacterial or viral infection.

Did you have necropsies done on the carpet pythons? How long did they take to die? Is this the only symptom? Have any of the afflicted animals shown any other symptoms before they expired?

All you are going to do is get people here tossing out some of the more common reptile diseases - which won't help you one bit.