I had trouble with this so once I got it I figured I'd share the method that I used.
It's not as step by step as some solutions because this can be done fairly quick long before the cure is finished.
The genes I used are as follows
Start in India
1.Evolve Blood 1, Water 1, Insect 1, Bird 1. (Transmission)
2.Evolve Drug Resistance 1 , Genetic Hardening 1. (Abilities)
**Allow mutations that are non lethal**
3.Evolve coughing if it hasn't already mutated. (Symptom)
**The cure might start but it is fine**
4.Now collect DNA points until you have over 53 points (with Sympto-stasis gene, without Sympto-stasis you will need 100+ which is still easy) as well as a noticably good chunk of red (infected)
**Save in a new save file just in case at this point**
5.Go to symptoms and devolve all of them, even coughing
6.Evolve Insomnia, Paranoia, Seizures, Insanity, Dysentry, Diarrhoea
7.Devolve Dysentry, Seizures, Paranoia, and Insomnia
At this point you should have only Insanity and Diarrhoea evolved
8.Go back to the world view and just let it play out for a moment.
For me it popped up saying I had the public defecation combo within 10 seconds on super fast speed. If it does not unlock for some reason re-load and redo steps 5-7.