The worked for me straight away;
I figured it out, the trick is to keep the lethality of the bio weapon all the way down. As soon as it starts killing people, they start working on a cure. The other big secret is you have to max out the three special abilities, which will then give you 'Armageddon.'
1. Start in a rich county. The goal is to spread the disease and not necessarily infect a lot of people. By starting in a rich country, their meds will keep it from coming too infectious too quick which will cause it to get noticed. As far as I know, this is a necessary step.
2. Keep it non lethal! You will have to constantly check the disease graph and make sure it doesn't become more lethal. Start with Gene Compression and then the deactivate genes. The purple line (lethality) should stay below the yellow line (severity line).
3. Transmit the disease. First step is to use the boat or airplane transmit, either way.
4. Keep up with the lethality! Bottom line, if they notice your bio weapon and begin work on a cure before everyone is infected, you lose. If the symptoms evolve, devolve them ASAP.
5. Infect the world. You will have to use every form of transmission (rat, mosquito, livestock, blood, bird, boat, and plane). I reccommend doubling the bird option. You will also have to upgrade the heat resistance and you may have to double the Blood option as well.
6. Destroy the world! If you infected 100% of the people without getting noticed, you win! Simply max out the Special Abilities and trigger the 'Armageddon' ability. If you don't have enough money at this point, then you can devolve some of your transmission abilities.
The death toll will rise way faster than the cure. If for any reason work is started on the cure before everyone is infected, you just have to try again.