pei fever

hi there
I have a dog who we have always suspected of having pei fever. Can anyone
tell me what an episode of this looks like? I feel he is having a bad couple
of days, where he walks with his tail down, has trouble walking, and has had
temperatures. There is nothing else wrong with him and he is eating fine,
but seems to crash out on these fevers and is sticking to me like glue
(which is unusual for him). Also what can i do to help him out during these
episodes. .