Don't worry they'll still need to breathe, it's just that humans aren't the only species that can hold their breath, albeit by a different mechanism 
Just spoke to DM on the phone and asked her about her childhood in a S London suburb and as an evcuee. She is early 80's, I am 60 this year, neither of us ever had nits - I've had them since, off the DC of course, and we were well aware you could catch them from other children. My threadworms as a toddler were the bane of her life 
She does recall there being a bit of a problem with fleas though, human fleas I imagine. And in my childhood there was a constant rumour that you could still get fleas in the flea-pit, as the cinema was often known.
It was only when ironing the seams of clothes became a part of life that human body lice became more or less extinct. We can't iron heads though

For the sake of completeness, I must confess that long ago in my promiscious twenties, I did get crab lice 
Very specialist, lice. Good demonstration of evolution in action - your basic human louse evolving to fill 3 very specific niches on the human body.
Just imagine having public lice, body lice and head lice (plus fleas - or maybe you couldn't have both at the same time?)