Over the past couple of years many of the kittens that our rescue group has fostered have developed what we call limping kitten syndrome. They are perfectly fine for several weeks, then all of a sudden they start dragging their hind legs. The next day they seem to be feeling sick, and the third day they are better, and the fourth day they are back to normal--no limping. The vet has no explaination for this. Has anyone had the same problem?