i would also check for parvo as there are stronger variances of it
P.S. There also may be a foreign object that has become lodged in his mouth & has caused an infection (The odor)......Thus, he cannot eat or open it.....
Hello & welcome
You need to get your guy to a Vet ASAP....Sounds like Periodontal Disease...Hopefully, it's an abscess tooth that can be pulled.....It's not that he won't eat, but that he can't because it hurts too bad....He will need antibiotics for the infection.....This will only get worse if left untreated....Call your Vet for an appointment, Tomorrow....Let us know what you find out.....Karla