Biology Games
Always loved these types of games. And I enjoyed your first one in 05 never thought that i'd see a sequel. I have to admit I was a bit intimidated by the poor reviews this had but I had no troubles at all until around stage 21 and above. I totally love these types of games and really enjoyed the difficulty curve that really challenges your quick reaction time.
As for the people who were complaining.. I'm playing with this shitty touchpad on a laptop. So it /is/ possible. Get your game on and start infecting!