Does My Foster Kitten Have FIP?

Q: Can you tell me why my foster kitten might have fluid in her abdomen? I was told she has feline infectious peritonitis (FIP). I rescued her litter in the beginning of May from our local shelter and they were maybe 6-7 weeks at the time. They all developed URIs and had diarrhea, and were treated for that. The URI took a while to clear; they still have a little congestion and watery eyes. One kitty developed fluid accumulation about two weeks ago; it became very noticeable as her sides were sticking out. It has only gotten bigger and her back is bony. I can feel her spine and tailbone. She eats, drinks, uses the litterbox and will still groom herself. She isn't completely active but she isn't lethargic either. I've taken her to three vets. Two think it is FIP and the other thinks it is likely but not saying it is yet. Her X-ray just showed a fluid-filled abdomen. They put her on Panacur, Albon and Baytril, hoping it was maybe due to parasites. Nothing has really changed.

I took her to a cat specialist today. Fluid was drawn from her belly and analyzed and the vet said it had characteristics of FIP fluid and that was what she thought it was. I'm wondering if there is anything else I should do to rule out other causes or determine it is in fact FIP. I am on a very limited budget and have gone broke with vet bills from my rescue animals. If it could be something else that I can possibly fix, I am willing to pursue it. I have cried my eyes out today knowing I will likely need to let her go and I just want to make sure that is the right thing to do and when I should do it. Anything you can share or offer would be so very much appreciated.
 
A: A young kitten from a shelter with an abdomen full of fluid and a very bony spine is very likely to have feline infectious peritonitis (FIP).  Other signs of FIP would be a fever that doesn’t respond to antibiotics, and a high level of globulins in the bloodstream.  You didn’t mention whether she had a fever or whether bloodwork was performed. The blood test for coronavirus antibodies (FIP is a coronavirus) cannot definitively diagnose FIP, but most cats with FIP will show a high level of coronavirus antibodies in their bloodstream. You didn’t mention whether you had this test performed or not. Frankly, I don’t think it is necessary to do any further diagnostics. The fact that your cat had the abdominal fluid analyzed and that it had characteristics of FIP makes me certain that this little kitten does indeed have FIP. Taking it to a feline specialist was a good idea, because FIP is a tough disease to diagnose. If she (and two other vets) feels that this is FIP, then it probably is. As you surely know by now, FIP is not a treatable disease, and all cats succumb to the disease fairly quickly. I commend you for taking these kittens from the shelter and for pursuing a diagnosis with such dedication.