Cagaster of an insect cage question

So, I been watching the anime and I was wondering if we ever find out how >!Qasim and Lazarus got infected. In their episodes, they never got impaled or bitten by the cagasters yet they turn. How? The only answer I can think of is something airborne or consumed but I don't recall either happening.!<

Thank you for your time, it's an interesting anime but that's one question I'm still left with.