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It may take weeks, months or even years for your known infected kitty to show signs of the infection. Your other cats are at great risk of getting Feline Leukemia especially since they have already had contact with an infected cat without being vaccinated. The other cats should be immeciately tested and vaccinated for Felv. You should seperate the uninfected cats immediately not allowing them to share a litterbox or food or water bowls with the infected cat.
Here are some tips I found on how to manage your infected cat:
There are also many treatments for FelV see: