Hello I am Dr. Joey. Thanks for trusting me to help you and your pet today. I am a licensed veterinarian with over 15 years of experience. I look forward to working with you.
I must agree with you that parvovirus is not very likely in an older adult dog, especially if he received his vaccinations regularly. If, however, he had never been vaccinated and your vet did a parvotest, which was positive, then it is possible to be parvo. However, what is more likely is that either he had hemorrhagic gastroenteritis syndrome (causes profuse vomit/diarrhea with blood and is very responsive to intravenous fluid therapy and medications) or he had a different virus (like coronavirus) that caused the issue. Rarely we can see Addison's disease cause problems that look like parvo but he probably would not have responded so well to treatment until the cure for this condition was administered, and your vet should have picked up on this with lab work. And finally ingestion of an unusual item that severely upset his system is very possible.
With regard to your other dogs, the fact they are normal does make it more suspicious that this was a problem that only affected Rocky.
Is he now improved? I am unclear on that. If not, then I would probably reassess if this could be Addison's disease. Sometimes we do not see the electrolyte problems in cases (causes high potassium), and the dog only has the glucocorticoid deficiency which leads to the digestive tract problem. Your vet can easily screen for this and while waiting for those results given a steroid to help him improve.
If your vet is sure this is not Addison's and he is not improved, then I would reassess if he might have swallowed something. However, let me circle back to parvovirus for a moment. AGain, if he was never vaccinated and the test your vet did in-house was positive then this could be the problem and treatment in older dogs who gets this takes a lot longer (sometimes hospitalization of upwards of 7 days is necessary). The oldest patient I have treated that I was confident had parvo was about 4 years old. He was very ill, but did survive with good supportive therapy.
And if this is parvo, then you must vaccinate your other dogs ASAP. It will not help prevent them from getting this as the vaccine must be boostered in 3 weeks to even hope that a dog is immune. But it will help because it means the virus has infiltrated your yard where you cannot get rid of it, and your other unvaccinated dogs would be at risk. I will be hopeful that everyone is vaccinated so this is not a concern for you.
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