Two weeks ago on 8/14 I (26F) took my indoor only cats (spayed female, neutered male, 4YO from the same litter) to the vet for a checkup and vaccines (which I note, the distemper vaccine had lapsed by about 6 months). They are otherwise healthy. At the vet, my female cat lost her mind and went crazy in the room and was hiding under the table. They were able to do her vaccines and everything was fine.
The following weekend, my female cat developed a limp and throughout the week continued to decline, couldn't jump on things, had an extremely decreased appetite, quit drinking water, hissing at me, not playing, and was hiding. All signs of being sick. I took her in, she had a 103 fever and had lost weight. They kept her for the day, gave her fluids and did blood work. Blood work only showed slightly high neutrophilis and monocytes (attached). X-rays showed no injury. They administered Meloxicam and some IV antibiotic. She came home and has been doing better.
3 days later, my male cat started exhibiting ALL the same symptoms and lost a whole pound. I just took him in. They did blood work, gave him an antibiotic, fluids, and a different NSAID. They said they have no idea what this "mysterious" illness could be. I asked if they could have picked up a virus at the vet (perhaps Calicivirus bc of the limp/joint pain) and they said there was no way because we were the first appointment of the day so there should have been no exposure to other sick cats.
So the question is, wtf is going on with my cats?! I haven't changed anything else except started offering a high fiber food alongside their regular food at the vets suggestion to help female cat with hard stool. I am so vigilant, cautious, and careful with these poor babies. I am waiting on male cats blood work but it's just so crazy to me that literally $1200 later I have no answers. It freaks me out because I have no idea how else I could have prevented this. I am very fortunate to be able to afford this vet care. Lemonade insurance has been great, I highly recommend. I have only had to pay a fraction of the total bill here.
Any advice, words of reassurance, or constructive/kind comments welcome. We are located in central Florida.
TLDR; Young healthy indoor cats both got some virus/illness that showed up after routine vet visit and vaccination and veterinarian is not sure what it is or how they got it.