You need to get clarification from your doctor on the risks associated with cleaning the litter box and being around the cats.  Ask him or her specifically about using the vacuum and the risks that your husband is concerned about ("air borne").  Once you have all the information then you wil be in a better position to discuss the issue with your boss and let her know that, in your opinion,  balancing the litter box cleaning versus the risks associated with the litter box cleaning it is not worth putting your unborn child and you at risk. Be prepared, though, for repercussions as she sounds like the kind of boss that wants what she wants when she wants it.  Good luck.