Most of this guide was created by trial-and-error, but I had other guides as a reference too and would like to especially mention All Hail Spicy for his guides.

If you got this far into the game then you probably have unlocked all the previous genes (if not, you have to since we will be using some of them in this walkthrough).

Recommended Genes


Starting Country
As with most guides, I'm going to stick with Saudi Arabia here too. Continue evolving in the following order as soon as you get enough DNA (don't worry about any mutations):

• Pharyngitis
  
• Sneezing
  
• Air I
  
• Water I
  
• Drug Resistance I
  
• Cold Resistance I
  
• Air II
  
• Water II
  
• Extreme Bioaerosol
  
• Drug Resistance II
  
• Cold Resistance II

Now we relax and pop bubbles while the rest of the world gets infected.

If cure progress reaches 25% evolve Simian Neuro-Genesis. Wait till the whole world is infected (There are no healthy people left in the world), and evolve the following:

• Neuro-enhancement I
  
• Neuro-enhancement II
  
• Neuro-enhancement III
  
• Total Brain Death

Evolving Total Brain Death means the virus becomes lethal to humans, therefore we go ahead and evolve the following lethal symptoms as well (chances are, some of them have already been mutated):

• Pulmonary Haemorrhage
  
• Haemorrhagic Shock
  
• Internal Haemorrhaging
  
• Hydrocephalus
  
• Meningitis
  
• Coma
  
• Gastric Ulceration
  
• Hypocoagulability

The End-Game
By now you should be killing off humanity really fast, and if you feel the cure progress is still too fast you can evolve Genetic Re-Shuffle I and Genetic Re-Shuffle II.

Gene Trick
Now comes the most important part - once you are close to killing off all of humanity, save the game, finish the game, unlock a gene, load the saved game, finish it and unlock another gene - and repeat as many times as needed.


As you can see from this screenshot, I saved the game with only 28k infected left in the world - this meant I only had to wait 3-4 seconds each time to end the game (and thus, unlock genes).

Conclusion
This walkthrough should work for you, it worked for me the 3x I played it.

Enjoy!