PB
Years ago I happened on a site that said the 1918 flu was a bioweapon made from visna virus and one other thing I can't remember. I think that event went even deeper, but reading that laid groundwork for my future thinking. Given how CFS can have symptoms manifesting anywhere in the body (ask me how I know), I think it was created by kluging together multiple disease vectors in order to hit any of the body's systems, neurological, digestive, hormonal, cardiovascular, whateva. So sure, why not something with an olfactory pathway.
I haven't done any digging for quite some time, but there was DeFreitas with that spumavirus in the gut, for starters.