This scenario doesn't behave like any conventional disease. It has very little cross-country transmission (similar to Fungus) and causes a great deal of world panic (resulting in very early port closure).

To infect the world, you need to open anomalies -- which behave like Spore Bursts. Each anomaly will automatically close after a few days or weeks -- which is controlled by a variable rate of symptom mutation -- or you can close them yourself.

There are 12 anomalies available:

2 infectious agent incursions (the first of which is evolved by default)
2 harmless creature incursions
5 dangerous creature incursions
2 lethal creature incursions
1 convergence event

Most anomalies only open in a single country. One of the dangerous creature anomalies opens in 5 countries. The convergence event opens in 25 countries! But you can't evolve convergence right at the start -- before you can do that, you must have opened (and closed again) both of the infectious anomalies and 1 of the dangerous creature anomalies.

The infectivity, severity and lethality are incredibly erratic -- jumping wildly up and down, as anomalies open and close. Passive strategies won't work. Playing at Normal level, you can infect most of the world before adding much lethality, but you can't avoid severity for very long. Playing at Mega-Brutal, you need to start killing people pretty much straight away :-)