Who said a circuit of the continent? But any jihadist willing to blow himself up to kill a handful of infidels will be thrilled at the chance to indirectly kill millions, just by riding a subway while infectious.
What makes you think they would NOT? They will behead children, rape little girls and boys, but suddenly being sick will stop them in their tracks? Really?
A terrorist can spread the virus without being sick. All they need to know is how to keep it alive and spread it effectively.