Can a cat get a viral disease like FIP/FIV/FeLV without fever?

Fevers can come and go with any ongoing infections including FIP in what is often referred to a 'waxing and waning' condition. This would not be definitive for any specific disease but does indicate that the condition is not being fully resolved and is triggering inflammatory responses

While Bills certainly could be positive for FeLV or FIV it would be pretty unsusal for him to be symptomatic for the diseases at his age. Parasites don’t typically cause a fever either. If he still has a fever I’d recommend having your vet examine him - some other kind of infection is possible and it is concerning he isn’t responding to antibiotics.

I understand you are concerned about FIP. The reality is, if you don't have money for a veterinary visit (and in many cases even if you did), FIP is typically fatal and untreatable. The best thing you can do is separate your sick cat from your healthy one and see how things transpire over the course of the next few days. Typically, cats with FIP, regardless of the form, will be inappetant and not wanting to eat anything at all. The worst form of it will cause massive fluid buiid up in the chest / abdomen and result in difficulty breathing. The other form typically produce clinical signs that are both ophthalmic and/or neurologic, plus several other non specific clinical signs (a couple of which include what you are descrbing). Overall, FIP would not be near the top of my list. I would definitely make sure all three cats have been tested for leukemia and AIDS however in order to rule both of these life-threatening conditions. While not as rapidly fatal as FIP, both conditions can carry poor long term prognosis. It sounds like the one cat with a fever and swollen belly might benefit from pain management and a recheck for the presence of worms. While dietary indiscretion could be an issue, it is not likely to cause a fever unless an infectious organism was present in the food. Hope this is more helpful than my previous response.

Keep in mind that many diseases have similar symptoms, so the only way to definitively know if a kitten has a specific disease is to be blood tested for it, and I do recommend having that done if you suspect your kitten may have one of these diseases. Kittens born to mothers infected with feline leukemia can have it, and symptoms include anorexia, slow and progressive weight loss, poor coat condition, enlarged lymph nodes, fever, pale gums and other mucus membranes, persistent diarrhea, eye conditions, and infections of the skin amount many other symptoms. Symptoms of FIV include fever, poor coat condition, anorexia, diarrhea, eye conditions, infections of the skin, bladder, and upper respiratory tract, weight loss, and various types of cancer and blood diseases which are more common in cats with FIV.

I agree, those symptoms are concerning for intestinal, oral, or kidney disease. Unless the test was falsely positive, cats don't outgrow FIV. There is also no cure for the virus, though not all cats that have it will develop disease. I would recommend that Tiger get checked out by the vet. After a thorough physical exam and review of his symptoms, the vet may recommend bloodwork, urinalysis, or x-rays to see what is going on. Here is more information on FIV in cats: https://www.petcoach.co/article/feline-immunodeficiency-virus-fiv-in-cats/

This seems unusual - FIV is a viral disease and vaccines would not be considered a trigger. It’s difficult to know whether or not these symptoms are related to FIV without knowing the results of the confirmatory test or the other lab work. If she does have FIV it’s possible that she could live a normal life span although she will be predisposed to infections in the future. Your vet may want to run more tests to look for infections.

What you describe could be feline distemper. It could be feline infectious peritonitis (the dry form) or another viral infection. Whatever ever is is, Butternut needs to see a veterinarian as soon as possible. Keep Buttermilk as comfortable as possible, leave plenty of fresh water available, offer canned food or even boiled chicken breast. Good luck.