Have you taken Buck or Jefe anywhere other dogs have been where they could have picked up the virus? I really don't think it is parvo. If Buck is a healthy dog and up to date on his shots (and especially since he's an adult), there's a very low chance of catching parvo. I bet he got into something. A parvo test can be done to him quickly - if the test is positive, they know for sure. If the test is negative, there is still a slight chance he has it, but he probably doesn't. So maybe you can ask your vet to do one. I can't imagine any vet who wouldn't do one right away with those symtoms.

Anyway, even if the puppy goes and gets shots, he is still VERY suseptible to catching it because he is so young and his immune system is not fully developed. You're gonna have to keep him away from everywhere where Buck went to the bathroom. If it were me, I would even quarantine the pup to one room so there's less of a chance of being exposed. Parvo stays in the environment for a long time and is very hard to kill the germs. At the shelter, we just throw away the bedding that parvo pups use because it is so hard to completely disinfect the virus.

Good luck and my prayers are with Buck.