I followed this guide exactly and got it:
http://icspicy.blogspot.com/2014/04/plague-inc-nano-virus-gu...ATP Boost - we'll need this because we're going to evolve a few stuff before selecting a country to start in.
Aquacyte - makes those hard to reach island countries, that are only accessible by ship, easier to infect.
Sympto-Stasis - this gene stops the increase of DNA costs of symptoms every time you evolve but it increases the speed of the cure progression. This is probably the most important gene to have.
Genetic Mimic - slows down the cure progression. The primary reason we need this is to counter the cure speed increase that sympto-stasis has.
Extremophile - gives a small boost on every climate. Very useful.
1. Before selecting a country to start in, we'll need to evolve a few things:
Code Fragment Interception
Coughing
Cysts
Hyper Sensitivity
Insomnia
Paranoia
It might seem that you won't have enough DNA to evolve everything above, but you do. Insomnia and Paranoia costs nothing to evolve.
2. Start in China or Saudi Arabia (Saudi seems to be recommended a lot by other people and its airplane paths really provide a boost into infecting countries sooner)
3. Evolve the following symptoms in any order you want. I recommend evolving the cheaper ones first
Rash
Sweating
Nausea
Vomiting
Pneumonia
Sneezing
Abscesses
Anaemia
Haemophilia
4. Continue by evolving the next set of symptoms(if they aren't mutated yet), transmissions, and abilities in this exact order. It is highly recommended that you evolve something once you have the DNA to do so. Why? Because Genetic Shifts happen, and when they do they'd most likely increase the costs.
Code Segment Interception
Water and Insect 1
Paralysis
Coma
Skin Lesions
Diarrhoea
Water and Insect 2
Radical Elements Stabilised
Drug Resistance 1
Genetic Hardening 1 and 2
Drug Resistance 2
Seizures
Insanity
Cold Resistance 1 and 2
Necrosis
Dysentery
Encryption Breached
Replication Factory Overload
Genetic Re-Shuffles 1, 2, and 3
Heat Resistance 1 and 2
By following this order of evolution, cure progress won't even hit 70%. Again, evolve every time you get the needed DNA.
5. At this point, you'll have to wait until the whole world is infected, you'll get a prompt saying that there are no healthy people left. Once this happens, evolve every lethal symptom you can. I suggest getting Total Organ Failure and Hemorrhagic Shock maybe even Internal Hemorrhaging. There are times though that you will have enough DNA to evolve every remaining symptom.
6. From here on, people will start dying fast. Wait for a pop-up saying something like "Nano-virus is about to eradicate humanity", after that shows up evolve Broadcast Interceptor Overload. This significantly lowers the cure progression which in turn boosts your highscore.
*edit*
A couple people were having issues with this and Elite1111111111 posted the following in comments and it seems to have helped
"Lost 5 times in a row to borders shutting down. What helped me (or could have been a coincidence) was waiting at Step 4. At Step 4, I only evolved things that weren't symptoms. Every symptom at step 4 causes lethality (except Skin Lesions). I think a lethal cure causes people to close their borders faster. So when I got to step 4 I just focused on increasing infectivity and slowing the cure. Once all the islands were infected I grabbed all the symptoms."
So thank you to Elite and hopefully that will help anyone with issues. And again, of course, thanks to the people that came up with the guide that I used in the first place