Are your rabbits indoors?
Carried by insects/fleas I think so don't think your hubbie will bring it back to the house as such.
Only got one house bunnie and he was vaccinated until this year. Missed it I'm afraid

We make sure our house cat wears a flea collar as when we first took her in she had very scabby ears which the vet said was caused by rabbit fleas attaching to her ears while she was out hunting them for her dinner. We were worried she would bring them in the house and they could infect bunny with myxi - have seen one or two up here with it.
Sorry no other ideas. Think Colliewoman knows her rabbits - perhaps she'll have some thoughts on it.