I just adopted 2 12-wk old kittens. They are males and were neutered 6/29 and given their first 4 in 1 shots. They were also tested and found negative for FELV. The first day at home they were constantly active. 24 hours later the smaller kitten suddenly started favoring his right paw, and cried if I touched it. He was constantly sleeping and if I tried to rouse him he would not stand up - just flop over and go back to sleep. When he walked he was very wobbly, as if drunk or as if his head was too heavy to hold up. No sign of any injury but the joint above the paw looked a little swollen. Took him to the vet later that afternoon where, right in front of the vet, he switched to favoring his left paw - wouldn't put any weight on it. He was found to have a temp of 104 F so the vet gave him amoxicillin and sent him home. That night the second kitten started favoring one paw and showing signs of lethargy too. Both kittens are eating fine, using the litter box fine and seem pretty responsive when they are awake, but I am really worried about this mysterious illness. They seem slightly better with 1 day of amoxicillin, but do they need something else? Can this spread to the 2 5-year old cats who already live here? They are all strictly indoor cats at all times. There are no signs of fleas or any other parasite, but since they were rescue kittins I don't know if they were suffering from parasites before being adopted. I would really like to know what this is and whether it can be transmitted to the 2 adult cats in the house.