Diarrhea and Cats-Next Is Elizabeth Taylor

Tonight Elizabeth came down with diarrhea. This time, I was prepared: gave an antibiotic that Jimmy and Katharine are taking; gave some fluids by mouth; gave .10 Buprenex (helps with fever and pain.) We have enough antibiotics for three cats Monday and I'll get more hopefully Tuesday. I would premed the rest but you shouldn't give an antibiotic unless there's cause. Trying to figure out where this came from and when. Baby was the first to go to the vet, to take Dasaquin for possible joint pain, and then develop diarrhea for which she received Metronidazole. A week later, Jimmy began diarrhea once a day, and then after a couple days, twice a day, and then last Tuesday, four times. Then Katharine began Thursday. And now Lizzie. Meanwhile, Cooper was in the ER May 11. Either Baby brought home a virus from the vet or Cooper brought it home. Either way, this isn't attacking the kitten siblings in the order of which they normally share an illness and get sick so that's a puzzle. Why has it jumped around? Thankfully, it's just a mild temp and diarrhea and not other symptoms. We'll see if giving Lizzie an antibiotic at first sign will prevent the others from getting it or if it's too late and someone will get sick in a few days (which remain-Bette and Myrna and maybe Cooper.) It's not what they ate or they'd all be violently ill and they all don't eat the same thing. Baby did go to the vet with Katharine so why didn't Katharine bring it back and get sick when Baby was sick? We had a stool sample checked and there are no parasites. Puzzling.