I rescued a mom from our city pound in February. At the time she had three kittens, all of whom appeared to be a couple of hours old. I snap tested her (ELISA), and she was a faint positive for feline leukemia. We left the babies with her, since we didn't have anywhere else to bottle feed.
When the babies were about 5-6 weeks old, we retested mom and the babies. Mom now tested as a strong FeLV+ on the snap test. We did an IFA test, and mom tested negative. We suspect the mom got FeLV from sex with the kittens' dad, and so it has not yet him her bone marrow and is not showing on the IFA. This might also be good for the kittens, since it might mean that they weren't as exposed in utero.
We tested each of the three babies, and they all were negative for FeLV on snap tests. After that, we separated mom and babies so that they would stop nursing and have a better chance at not contracting FeLV (if they haven't already), and of converting to negative in case they already have contracted it.
My question is, when should I retest the babies? I know that even though they tested negative, they were nursing up to that date. How long do I have to wait to be sure they have not contracted FeLV? I have read all over, and there doesn't seem to be a consistent answer. They were last with their mother on April 7. They seem very healthy-- no URI, good poop, healthy weight, good eaters, and tons of energy.