IIRC Spot devolved into an iguana. (It should be noted into a FULL iguana. Now, obviously this is because in production terms it's easier to get an iguana than it is to glue a punch of iguana-like appliances to a cat but "in-show" it has some implications on the ultimate terminus of the "disease." Spot was a cat, possible a small enough and "simple" enough a creature for the de-evolution to quickly occur. This could mean everyone else would have continued to "de-evolve" until they reached the "full version" of whatever they were becoming. I could be argued that Riker, Nurse Ogawa and Worf were already there. (Which begs the question on why they wouldn't *keep* "de-evolving" from even that. Was the ultimate route of this infection for everyone to become single-celled organisms? Simple proteins? Ehh, I'm sure the transporter or Data cure-all embryonic juice would've brought everyone back to perfect health anyway so we can all have a good laugh at Barclay's insecurities.