Can A Kitten Have Feline Parvo And Not Have It Become Active? Does It Have To Affect Them?How Long Is The Incubation Time?

I had 2 kittens that I rescued from the Humane Society, they were not tested for Feline Parvo and had only received one vaccination when they should've already had all 4 and recently one of them died. I have been informed that the other one has it too, Will it in deed act up and make him sick or can he just be a carrier? Can he carry it but it may not become active and how long is the incubation time for it?