I have a pretty good Nano-virus strategy that I've figured out. So far my best score is about 59,000 and 5 out of the past 6 games have been above 50,000.
Start in Saudi Arabia As soon as you pop the first red bubble, buy Insomnia and Paranoia You should now have 3 DNA points so buy Code fragment interception Buy Air I (cure should be 20-30%) Buy Code segment interception (cure should be 30-40%) Buy Air II (other countries will get infected very soon after this) Buy Water I/II Buy Extreme Bioaerosol
At this point, the cure should be anywhere from 75-95% complete.
If the cure is 75-85% complete, buy Drug resistance I followed by Blood I If the cure is 85-90% complete, buy Drug resistance I
The key here is that when the cure reaches 95%, you have the 6 or 7 DNA points to buy Radical elements stabilised. You want to put this upgrade off as long as possible, so buy Drug resistance I and Blood I if you can without risking the cure completing.
As soon as you buy Radical elements stabilised, buy: Genetic Hardening I/II Seizures Insanity Inflammation Paralysis Coma
Next buy Drug resistance I and Blood I if you haven't already
Buy Cold resistance I/II Buy Drug resistance II Buy Drug immunity (near the special abilities)
Next you want to get to Necrosis. Go through the coughing route unless Rash has been mutated (in which case you go the Rash route).
At this point, sometimes my DNA points jump by like 80. Not sure if this was a glitch or if so many people were dying that I got 80 points in a second.
Once you have bought Necrosis, save your money until all countries have been infected and the last infected country (and Greenland) have at least 1000 people infected.
Buy Total Organ Failure (postpone by about 15 seconds if Dysentery or Hemorrhagic shock mutated on their own)
At this point the whole world should be infected or close to it.You can spend your DNA points on whatever you want but make sure that you save AT LEAST 20 for the next step.
The last step is the most critical for getting a high score. Once the world population reaches around 10,000-20,000 (pay attention because it happens quickly), you need to buy Broadcast Interceptor. The timing of this is very important because the Broadcast Interceptor will lower the cure by around 10-15% but only for two weeks so you MUST win the game within that time for the 10-15% lower cure.
At the end you should have between 30-45% cure completion and it should take 350-450 days. On my best run, I ended with 30% cure and it took 353 days. The final score ended up being 58960 which is my best with any disease type.
I hope this helps anyone who has trouble with Nano-virus or anyone going for a new highscore. This mutation order is what I have found to work the best for me but there will probably be things that can be tweaked and improved. If anyone finds some way to improve this strategy please let me know.