Feline Leukemia is kind of an odd virus. If you're not familiar, the current thinking seems to be that adult cats are relatively (though not entirely) safe from contracting it; kittens on the other hand are at a good deal of risk. They can get it from peers or from their mothers - sometimes it makes them sick, sometimes it doesn't.
Then what happens is the virus seems to sequester itself - in the bone marrow, or somewhere - after which the cat will be asymptomatic. Somewhere down the line, however, something - stress, another disease, something - triggers the virus to come out of hiding, and begin multiplying, with attendant negative effects. Death can be slow, or amazingly fast.
So, thanks for the lecture, but what does this have to do with me? In 1999 I lost my other cat, Morphia, who had been raised with Xiombarg from kittenhood, to an astonishingly rapid (to me at least) onset of Feline Leukemia. Now the odd thing was that Xiombarg was a street rescue, but Morphia was raised entirely as an indoor cat until she was two or three years old. So it seemed likely that Morphia would have gotten FLV from Xiombarg at some point in their childhood, and simply happened to serioconvert first.
But... Xiombarg tested negative at the time of Morphia's death, and in 2002 when I took her in for an unrelated complaint. And again yesterday, too - so at this point it's probably safe to say she's clean. About which I am amazingly happy, no lie.
I can think of one other possible instance in kittenhood that Morphia was in contact with another kitten she could have picked it up from; interestingly enough it was what caused me to get Xiombarg in the first place. I looked after a friend's kitten for a week, and when she went home again Morphia clearly missed her companion, and moped around the house looking for her. So we decided to get another kitten of our own, and adopted Xiombarg.
And that, as they say, is that.