This simple exploit of current game mechanics makes a joke of one of the harder disease types!
(When playing nano-virus, they are aware of and curing your virus from the start)
It requires only that you have unlocked (and equip) the 'Sympto-Stasis' genetic code upgrade when setting up your game. Genetic codes are unlocked by winning a game on any difficulty with any virus type.
With Sympto-stasis equipped, the cost of symptoms does not increase as you evolve them.
The nano-virus has 2 symptoms that actually -GIVE- DNA when you take them, and this virus type has a natural ability where devolving costs don't rise (default cost of devolving gives 2 DNA). These are Insomnia and Paranoia. Simply buy those 2 and then repeatedly devolve/evolve paranoia for unlimited, free DNA.