Jan- and others- I had a pregnant stray who had 4 healthy kittens that at age 5 weeks suddenly began to weaken and loose balance, all in various degrees. I believe the exercises prescribed did help some (loose towel ramp to make them climp up and down to strengthen muscles) but their ch was from mother who, I was told, likely had distemper AT SOME POINT in her life (ie not contracted during pregnancy necessarily) and she survived it but it is dormant, so to speak in her system. (perhaps they develop antibodies that aren't transferred to fetuses?) Remember her- she's in Rockport now with her kids in a good home...