I'll start with a quote from my mom, "Having head lice is not shameful, but keeping them is!"
You can relax about the chickens, lice are pretty species specific. Even in humans, there are three distinct species of lice - head, body and pubic, and each tends to prefer it's own environment and has anatomy designed for it. IE, head lice and pubic lice have different types of claws/legs - one for coarse hair and the other for head-type finer hair.
While a stray lice from the chickens might get on you if you have a really bad infestation, they won't be able to reproduce on you and would die within a day or so.
Head lice are endemic and they could get them from just about anywhere. Good news is that they can only live about 24-48 hours tops off their human host.
I've become quite an expert on headlice - we got them in our house this summer from a toddler friend of ours who got them probably at a birthday party. My daughter and one son got them, as well as the toddler's mom. Needless to say, it was all out war to get rid of them. While I had them, my husband who was sleeping right beside me all that time never had a one, but we were careful not to get our heads where they were touching.
Sharing hats and hair brushes, or little kid having direct head to head contact etc are the most easy ways they spread, but they don't spread as easily as people think - they can't jump or fly, for instance. It usually takes direct contact to catch them from someone. Which, of course explains how I got them since I'm always rubbing heads with the kids - it's a quirky sign of affection in our house.
Nix was the best stuff we found to use, along with combing or cutting out the nits as you find them. Use the shampoo as directed, then comb EVERY DAY very thorougly using good light and a magnifing class. Then use the medicated shampoo again in 10 days or as directed, and comb again for another couple days. The shampoo kills the living lice and the combing will get out any eggs. White or clear eggs are the cases of eggs that have already hatched. Dark eggs are the ones that have baby lice inside.
Hope this helps!!