How can a baby kitten transmit feline aids and feline leukemia to adult cats?

I understand I have to keep my baby kitten away from my adult cats until the kitten is old enough to be tested. How would the kitten transmit the diseases if she, in fact, had them but was too early to test? How “away” is away (i.e., No contact at all? Nose to nose OK? Can they share food? Can they share litter box?)