lice and nits

Question
I emailed you last night about the shelter rat who had received 2 doses of oral ivermectin and 2 doses of injectable ivermectin withing the past month. I applied 3 mg of selamectin to him yesterday and you told me he should be parasite free in about 48 hrs...
I disinfected his cage at the shelter today (he is still staying there until I am assured there are not lice) and although his skin looks a lot healthier I can still see small nits attached to the hair even after using a flea comb.  
I had wanted to bring him home within a few days but am wondering if nits attached to hair could be dead or still live  eggs ????
Do the nits fall off when the selamectin works???
Thanks a whole lot
Maureen
Also how often can selamectin be applied ; I had thought it would need to be another month ; am I correct?


Answer
The nits should fall off and in fact, they may be off by now.
Also, I would put a new application on her after 1 month just in case there were eggs that were missed. Usually though, the eggs take 2 weeks to hatch so if there were any, the selamectin should still be in her system working to kill the nasty bugs.