Does Odo even have cellular structure? In "A Man Alone" and "Broken Link", it's suggested that his humanoid form has DNA, but that, too, may be part of his mimicry act rather than something inherent in Changelings...
Then again, the folks at Starfleet Medical, Starfleet Intel, Section 31 and whatever understood Changeling body chemistry well enough to devise the deadly but cunningly slowly acting bioweapon. It can't be too exotic, then.
Ironic how it seems that the Link turning Odo into an actual humanoid cured him of the disease, or at least drastically slowed its progress, so that the entire Link got the symptoms before he did... Seems the disease engineers truly understood something about the fundamental nature of Changelingness.